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Kingdoms of Life: Kingdoms of Life explained, sort of

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Kingdoms of Life: Kingdoms of Life explained, sort of

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Scientists have a system to group all the living things so they can study them. One of the ways of grouping or classifying them is called the Kingdoms of Life. But exactly how many Kingdoms of Life there are is not an easy question to answer. Find out why.

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Science Trek | Kingdoms of Life: Kingdoms of Life explained, sort of

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Plant Evolution

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National Geographic Animal Encyclopedia

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Copyright © 1996-2015 National Geographic SocietyCopyright © 2015-2026 National Geographic Partners, LLC. All rights reserved

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This article from Kremp Florist provide a timeline of plant evolution through years. You will learn all there is to know about how plants have evolved.

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Plant life on Earth is much older than we thought

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Plants appeared on Earth 100 million years earlier than scientists previously thought.

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© 2021 American Association for the Advancement of Science. All rights reserved. AAAS is a partner of HINARI, AGORA, OARE, CHORUS, CLOCKSS, CrossRef and COUNTER.

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Earth is the planet of the plants-and it all can be traced back to one green cell. The world's lush profusion of photosynthesizers-from towering redwoods to ubiquitous diatoms-owe their existence to a tiny alga eons ago that swallowed a cyanobacteria and turned it into an internal solar power plant.

By studying the genetics of a glaucophyte-one of a group of just 13 unique microscopic freshwater blue-green algae, sometimes called "living fossils"-an international consortium of scientists led by molecular bioscientist Dana Price of Rutgers University, has elucidated the evolutionary history of plants. The glaucophyte Cyanophora paradoxa still retains a less domesticated version of this original cyanobacteria than most other plants.

According to the analysis of C. paradoxa's genome of roughly 70 million base pairs, this capture must have occurred only once because most modern plants share the genes that make the merger of photosynthesizer and larger host cell possible. That union required cooperation not just from the original host and the formerly free-ranging photosynthesizer but also, apparently, from a bacterial parasite. Chlamydia-like cells, such as Legionella (which includes the species that causes Legionnaire's disease), provided the genes that enable the ferrying of food from domesticated cyanobacteria, now known as plastids, or chloroplasts, to the host cell.

"These three entities forged the nascent organelle, and the process was aided by multiple horizontal gene transfers as well from other bacteria," explains biologist Debashish Bhattacharya of Rutgers University, whose lab led the work published in Science on February 17. "Gene recruitment [was] likely ongoing" before the new way of life prospered and the hardened cell walls of most plants came into being.

In fact, such a confluence of events is so rare that evolutionary biologists have found only one other example: the photosynthetic amoeba Paulinella domesticated cyanobacteria roughly 60 million years ago. "The amoeba plastid is still a 'work in progress' in evolutionary terms," Bhattacharya notes. "We are now analyzing the genome sequence from Paulinella to gain some answers" as to how these events occur.

The work provides the strongest support yet for the hypothesis of late biologist Lynn Margulis, who first proposed in the 1960s to widespread criticism the theory that all modern plant cells derived from such a symbiotic union, notes biologist Frederick Spiegel of the University of Arkansas in Fayetteville, who was not involved in the work. That thinking suggests that all plants are actually chimeras -hybrid creatures cobbled together from the genetic bits of this ancestral union, including the enabling parasitic bacteria.

The remaining question is why this complex union took place roughly 1.6 billion years ago. One suggestion is that local conditions may have made it more beneficial for predators of cyanobacteria to stop eating and start absorbing, due to a scarcity of prey and an abundance of sunlight. "When the food runs out but sunlight is abundant, then photosynthesis works better" to support an organism, Bhattacharya notes. And from that forced union a supergroup of extremely successful organisms-the plants-sprang.

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Earth is the planet of the plants-and it all can be traced back to one green cell. The world's lush profusion of photosynthesizers-from towering redwoods to ubiquitous diatoms-owe their existence to a tiny alga eons ago that swallowed a cyanobacteria and turned it into an internal solar power plant.

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How seeds came to be. Shutterstock.

Curious Kids is a series for children of all ages, where The Conversation asks experts to answer questions from kids. All questions are welcome: find out how to enter at the bottom of this article.

Where did the first seed come from? - Alice, age six, Beverley, UK

Hi Alice. This is a clever question. As I'm sure you know, plants use seeds to spread their young and make new plants. But plants haven't always used seeds to do this. Seeds came together bit-by-bit over a really long time, as plants evolved.

To understand how this happened, you need to know that all living things change slowly over time, to get better at surviving in their environment - this process is called evolution.

Here's how it works: when a living thing has a feature which works well, it will be able to live longer and have more young. These young will probably have similar features, thanks to their parents.

Plants started using seeds to spread their young somewhere between 385m and 365m years ago. Before seeds existed, plants had other ways of doing this.

Shutterstock.

Back then, most plants used spores. Some plants today, such as algae, mosses and ferns, still do. You might have spotted the tiny brownish dots on the underside of fern leaves - these are spores.

Spores are different from seeds in a few ways. A spore is made of just one part - a single cell - while a seed contains many cells, each with different jobs to do.

Another difference is that spores only have one parent plant, while seeds have two.

This means that, after a seed starts sprouting, it can grow into a plant, just like its parents.

But spores have to work a bit harder: once they've travelled away from their parent plant, they grow into a little green plate of cells, which scientists call a "gametophyte". Then, two gametophytes must join together, before they can grow into a plant.

It's easier for gametophytes to join together when its wet - and that's why plants that use spores usually need to grow in wet places.

For example, horsetails are a very ancient type of plant, which like to grow along lakes, rivers and ponds: they have very strange spores with four "legs" which help them to move and travel further away.

The first seed

Scientists believe that an extinct seed fern, called Elksinia polymorpha, was the first plant to use seeds.

This plant had cup-like features, called "cupules", that would protect the developing seed. These cupules grew along the plant's branches.

Today, plants with seeds do things a little differently. There are two main types: "angiosperms" and "gymnosperms".

Angiosperms are flowering plants - their seeds develop inside of fruit, like apples, tomatoes or even rose hips or holly berries.

Shutterstock

Gymnosperms, such as pine trees, grow their seeds inside a hard cone.

The upside of seeds

Seeds have evolved because they are better at helping plants to survive than spores are. For example, seeds contain a food source to help the new plant grow.

They also have a hard coat, which helps them to live longer in different conditions: this means plants with seeds can life in lots of different places, from hot, dry deserts to cool, rainy places.

Seeds are so good at helping plants to spread their young that most plant species on Earth today use seeds.

CC BY-ND

Hello, curious kids! Have you got a question you'd like an expert to answer? Ask an adult to send your question - along with your name, age and town or city where you live - to curiouskids@theconversation.com. Send as many questions as you want! We won't be able to answer every question, but we'll do our best. More Curious Kids articles, written by academic experts:

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Curious Kids: where did the first seed come from?

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Curious Kids is a series for children of all ages, where The Conversation asks experts to answer questions from kids. All questions are welcome: find out how to enter at the bottom of this article. Where did the first seed come from? - Alice, age six, Beverley, UK Hi Alice.

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EarthSky | Updates on your cosmos and world

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Before we explain how seeds came to be, it's important to note one basic fact about plants. Land plants evolved from ocean plants. That is, from algae.

Plants are thought to have made the leap from the oceans onto dry land about 450 million years ago. And, as seeds are thought to have developed to keep plant embryos from drying out, it makes sense that the first seeds we know of are at least 360 million years old.

But what happened between 450 million years ago and 360 million years ago? This gap of about 100 million years indicates that some method of (land) plant reproduction predated seeds.

In fact, during this period, many plants used spores to reproduce. Some plants, like ferns, still produce spores. You might have even seen some spores shake out of those brown dots on the undersides of ferns - the brown dots are not the spores but the structures that produce them (the spores themselves are even smaller). A single plant can produce thousands or millions of spores at once.

During Earth's Devonian period, a group of plants called progymnosperms started manufacturing two sets of specialized spores: male spores, and female spores - the living tissues inside these spores produced eggs and sperm. Both types of spores were shed from the plant. But, if they landed close together, fertilization could take place. The new embryo could make a new plant.

Spores have some obvious vulnerabilities, though - they're very tiny, and have to survive and travel without built-in nutrition or physical protection. They also need water for fertilization to occur. In other words, spores aren't necessarily the most reliable means of plant reproduction-especially for plants living on dry land.

So, over time, some progymnosperms evolved into seed ferns. These seed ferns began producing female sex cells that stayed with the parent plant, and waited for male sex cells to arrive. These seed ferns slowly evolved into what are called seed plants.

In seed plants, the female sex cells (no longer numbering in the millions, by the way) still remained with the plant. But these plants developed special structures to "catch" male sex cells, otherwise known as pollen. This fertilization process was novel in that it did not depend on water; pollen was - and still is - able to be carried to a female cell by wind or flying insects.

Once fertilized, a seed plant embryo would grow inside an ovule, the part of the plant that housed a female sex cell. Tissue from the ovule developed the capacity to serve as a protective coating (a/k/a seed coating) for this embryo. This coating not only protected the embryo, but also protected the densely packed nutrition surrounding the embryo, once the embryo left the plant. (It bears mentioning here that another important function of a seed, beyond keeping a plant embryo moist, is to provide a developing embryo with nutrition. This stored food helps the embryo grow in the early stages of its development, and increases the young plant's chance of survival.)

And that's how seeds evolved!

In many modern plants, seeds are contained within a fruit. This fruit is useful in attracting birds, mammals, and insects, all of which help spread seeds around. On the other side of the spectrum, there are many "seedless" plants alive today, including ferns and horsetails - found in damp environments - as well as many aquatic plants.

Our thanks to:

Sir Peter Crane, Dean
Yale School of Forestry and Environmental Studies
Yale University

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How did plants develop seeds? | Earth | EarthSky

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Before we explain how seeds came to be, it's important to note one basic fact about plants. Land plants evolved from ocean plants. That is, from algae. Plants are thought to have made the leap from the oceans onto dry land about 450 million years ago.

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Plant Kingdom - Members of Kingdom Plantae

R.H. Whittaker gave the Five Kingdom classification for living organisms. He categorized living organisms based on multiple characteristics such as cellular structure, mode of nutrition, body organization, reproduction, phylogenetic relationship, etc. These five kingdoms were Monera, Protista, Fungi, Plantae and Animalia.

Let's learn about the plant kingdom, i.e., Kingdom Plantae.

Let us have a detailed look at the plant kingdom notes provided here for the conceptual understanding of the topic.
Also read: Kingdom Animalia, Plantae And Viruses
Plant Kingdom - Plantae

Kingdom Plantae includes all the plants. They are eukaryotic, multicellular and autotrophic organisms. The plant cell contains a rigid cell wall. Plants have chloroplast and chlorophyll pigment, which is required for photosynthesis.

Characteristics of Kingdom Plantae

The plant kingdom has the following characteristic features:

1. They are non-motile.

2. They make their own food and hence are called autotrophs.

3. They reproduce asexually by vegetative propagation or sexually.

4. These are multicellular eukaryotes. The plant cell contains the outer cell wall and a large central vacuole.

5. Plants contain photosynthetic pigments called chlorophyll present in the plastids.

6. They have different organelles for anchorage, reproduction, support and photosynthesis.

Explore More: Photosynthesis.

Recommended Video:

Classification of Kingdom Plantae

A plant kingdom is further classified into subgroups. Classification is based on the following criteria:

1. Plant body: Presence or absence of a well-differentiated plant body. E.g. Root, Stem and Leaves.

2. Vascular system: Presence or absence of a vascular system for the transportation of water and other substances. E.g. Phloem and Xylem.

3. Seed formation: Presence or absence of flowers and seeds and if the seeds are naked or enclosed in a fruit.

More to Read: Seed And Fruit Formation - Seed Dispersal

The plant kingdom has been classified into five subgroups according to the above-mentioned criteria:

1. Thallophyta

2. Bryophyta

3. Pteridophyta

4. Gymnosperms

5. Angiosperms

Thallophyta

Thallophytes lack a well-differentiated body structure and the plant body is thallus like.
Explore More: Thallophytes
Thallophyta includes plants with primitive and simple body structures. The plant body is thallus, they may be filamentous, colonial, branched or unbranched. Examples include green algae, red algae and brown algae. Common examples are Volvox, Fucus, Spirogyra, Chara, Polysiphonia, Ulothrix, etc.
Extended Reading: Bryophyta
Bryophyta

Bryophytes do not have vascular tissues. The plant body has root-like, stem-like and leaf-like structures. Bryophytes are terrestrial plants but are known as "amphibians of the plant kingdom" as they require water for sexual reproduction. They are present in moist and shady places. Bryophyta includes mosses, hornworts and liverworts. Some of the common examples are Marchantia, Funaria, Sphagnum, Antheoceros, etc.

Pteridophyta

Pteridophytes have a well-differentiated plant body into root, stem and leaves. They have a vascular system for the conduction of water and other substances. Some of the common examples are Selaginella, Equisetum, Pteris, etc.

More Details: Pteridophyta

Gymnosperms

Gymnosperms have a well-differentiated plant body and vascular tissues. They bear naked seeds, i.e. seeds are not enclosed within a fruit. Some of the common examples of gymnosperms are Cycas, Pinus, Ephedra, etc.

Angiosperms

Angiosperms are seed-bearing vascular plants with a well-differentiated plant body. The seeds of angiosperms are enclosed within the fruits. Angiosperms are widely distributed and vary greatly in size, e.g. Wolffia is small measuring about 0.1 cm and Eucalyptus trees are around 100 m tall. Angiosperms are further divided into monocotyledons and dicotyledons according to the number of cotyledons present in the seeds. Some of the common examples are mango, rose, tomato, onion, wheat, maize, etc.

Further Reading: Angiosperms

Cryptogams and Phanerogams
Also Read: Difference Between Bryophytes and Pteridophytes
The plant kingdom is also classified into two groups:

Name the pigment responsible for photosynthesis in plants.

Chlorophyll is the pigment responsible for photosynthesis in plants.

Describe the criteria for levels of classification in plants.

The plant kingdom is further classified based on the following three criteria:

Explain the characteristic of Thallophytes.

Members of this class lack a well-differentiated body structure, or in other words, the body is not clearly divided into stem, leaves and roots.

Explain the significant features of Gymnosperms.

Gymnosperms include plants that possess a vascular system and a well-differentiated body structure. Furthermore, they bear seeds like the angiosperms, but they are not encased within a fruit. Hence, the term "Gymnosperm", which is derived from Greek word, gymno = naked and Sperma = seed.

List the characteristics of Angiosperms.

Seed-bearing plants

Seeds are enclosed within fruits

Presence of well-differentiated plant body

Produce flowers during their lifespan

Presence of two subtypes - monocots and dicots

Cryptogams - Non-flowering and non-seed bearing plants. E.g. Thallophyta, Bryophyta, Pteridophyta

Phanerogams - Flowering and seed-bearing plants. E.g. Gymnosperms, Angiosperms

To learn more about plant kingdom Class 11, its characteristics and classification, explore BYJU'S biology.

Frequently Asked Questions

Register at BYJU'S for more plant kingdom notes for reference.

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Plant Kingdom - Classification and Characteristics

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The Plant Kingdom includes all the plants, trees, flowers and seeds we see around us. Explore the characteristics and classification of kingdom Plantae.

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| Classification | Plant Evolution | Animal Evolution | Homology |

Prokaryotes, Algae and Plants

Present-day prokaryotes may resemble early fossils, but they are modern organisms that have successfully adapted to modern environmental conditions. They are found in some of the most extreme environments on Earth, including Antarctica, the depths of the oceans and deep in rocks, round deep-sea vents, and in boiling thermal springs and are ever present in our human environments, including cities, homes and the human body.

The Cyanobacteria (blue-green algae) are a group of prokaryotes that are extremely important both ecologically (especially in global carbon and nitrogen cycles) and evolutionary terms. Stromatolites, which are formed by cyanobacteria, provide living and fossil evidence of cyanobacteria going back 2700 million years. Today stromatolites grow only in shallow, salty pools in hot, dry climates (e.g. Shark Bay in Western Australia), and their abundance in ancient rocks implies similar environmental conditions in those times. Stromatolites and other cyanobacteria were the main contributors to the marked increase in atmospheric oxygen concentrations that began around 2000 million years ago. Today, cyanobacteria are found everywhere - in marine, freshwater and terrestrial environments and as symbionts e.g. lichen - and contribute up to 50% of the atmosphere's oxygen.

DNA evidence suggests that the first eukaryotes (green plants) evolved from prokaryotes (through endosymbiotic events) between 2500 and 1000 million years ago. Fossils of eukaryotes that resemble living brown algae have been found in sedimentary rocks from China that are 1700 million years old, while possibly the oldest photosynthetic eukaryote, Grypania, comes from rocks 2100 million years old. Note that the diversity of modern algal groups, and particularly of their chloroplasts, suggests that these endosymbiotic events were not unusual. Modern algae comprise a range of organisms with very different structures but identical photosynthetic pigments. This suggests that very different host organisms have formed a symbiosis with the same photosynthetic cells. That is, the algal groups must have evolved through separate endosymbiotic events, and the group as a whole is identified on the basis of a similar level of structure, rather than on its evolutionary origins. Such groups, where the members have several different evolutionary origins, are described as .

Cyanobacteria have a close evolutionary relationship with eukaryotes. They have the same photosynthetic pigments as the chloroplasts of algae and land plants. Chloroplasts are the right size to be descended from bacteria, reproduce in the same manner, by binary fission, and have their own genome in the form of a single circular DNA molecule. The enzymes and transport systems found on the folded inner membranes of chloroplasts are similar to those found on the cell membranes of modern cyanobacteria, as are their ribosomes. These similarities between cyanobacteria and chloroplasts suggest an evolutionary link between the two, and can be explained by the theory of endosymbiosis.

Reference Websites

For Microfossils, stromatolites, and cyanobactieria: http://www.uni-muenster.de/GeoPalaeontologie/Palaeo/Palbot/seite1.html

To find out more about living stromatolites see: http://www.calm.wa.gov.au/national_parks/hamelin_pool_mnr.html

To find out more about fossil stromatolites see: http://cushforams.niu.edu/Stromato.htm

General Overview
http://www.peripatus.gen.nz/paleontology/MaiLinEvo.html

Endosymbiosis explained:
http://www.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Bacteria/symbiosis.html

The earliest land "plants"

For 1500 million years photosynthetic organisms remained in the sea. This is because, in the absence of a protective ozone layer, the land was bathed in lethal levels of UV radiation. Once atmospheric oxygen levels were high enough the ozone layer formed, meaning that it was possible for living things to venture onto the land.

The seashore would have been enormously important in the colonisation of land. In this zone algae would have been exposed to fresh water running off the land (and would have colonised the freshwater habitat before making the move to terrestrial existence). They would also be exposed to an alternating wet and desiccating environment. Adaptations to survive drying out would have had strong survival value, and it is important to note that seaweeds are poikilohydric and able to withstand periods of desiccation.

The earliest evidence for the appearance of land plants, in the form of fossilised spores, comes from the Ordovician period (510 - 439 million years ago), a time when the global climate was mild and extensive shallow seas surrounded the low-lying continental masses. (These spores were probably produced by submerged plants that raised their above the water - wind dispersal would offer a means of colonising other bodies of water.) However, suggest an even earlier colonisation of the land, around 700 million years ago.

Bryophytes

The earliest photosynthetic organisms on land would have resembled modern algae, cyanobacteria, and lichens, followed by bryophytes (liverworts & mosses, which evolved from the group of green algae). Bryophytes are described as seedless, nonvascular plants. Their lack of tissue for transport of water and nutrients limits their size (most are between 2 and 20 cm high). Bryophytes don't have typical stems, leaves, or roots, but are anchored to the ground by rhizoids. They can grow in a wide range of environments and are : when the environment dries so does the plant, remaining dormant while dry but recovering rapidly when wetted. These features make them important pioneer species.

Reference Websites

General Overviews
http://scitec.uwichill.edu.bb/bcs/bl14apl/conq.htm
http://www.bio.miami.edu/tom/bil160/bil160goods/12_notes.html

Bryophytes
http://www.personal.psu.edu/users/s/d/sdc182/bryophyta.htm

The vascular plants

Cooksoniais often regarded as the earliest known fossil of a vascular land plant, and dates from just 425 million years ago in the late Early Silurian. It was a small plant, only a few centimetres high. Its leafless stems had sporangia (spore-producing structures) at their tips.

Rhynia is slightly younger but similar in appearance to Cooksonia.

Baragwanathia is much larger & more complex, with what appear to be spirally-arranged leaves. Baragwanathia has been described as a (a vascular plant). For such a complex plant to be present in the Silurian then land plants must have emerged much earlier, perhaps in the Ordovician.

These first land plants evolved from the green algae, with which they share a number of traits. All store energy reserves, as starch, inside plastids. Their cell wall is built of cellulose microfibrils and the photosynthetic pigments are chlorophylls a and b, plus b-carotene.

Reference Websites

For the Silurian period http://www.ucmp.berkeley.edu/silurian/silulife.html

Problems with life on land for plants

Radiation

damage from ultraviolet light

heat

damage to photosystems

Desiccation

extremely drying air

sporadic water supply

Dispersal

Fertilisation

Solutions to life on land
The poikilohydric lifestyle
Poikilohydric organisms include some green algae, cyanobacteria (blue-green algae), lichens, and the bryophytes.
The homoiohydric lifestyle
This is achieved by:

Controlling water loss (waterproofing, cuticle)

Controllable valves in cuticle for photosynthesis (stomata)

Replacing lost water, internal conducting tissue (xylem): vascular plants

3D structure: minimises surface area, provides support

Ventilated tissue for enhanced gas exchange (internal intercellular spaces)

All modern land plants - with the exception of the bryophytes - have these features.

There was also competition for light, leading to pressure to increase productivity, which could be achieved by increasing the area available for photosynthesis (evolving leaves) and/or keeping stomata open for longer. This meant that mechanisms for obtaining and transporting water also needed improvement. Thus, evolution was a slow, continuous, linked improvement in water relations and productivity increase.

Diversification of land plants

Once these features had evolved, there was a substantial diversification of land plants during the Devonian period (408 - 362 million years ago). These included lycophytes (the clubmosses are the best-known modern members of this group:), horsetails (e.g. Equisetum), and progymnosperms, intermediate between seedless vascular plants and the seed plants. While the early forms were small & lacked woody tissue, the first tree-like plants (including progymnosperms and tree-sized lycophytes) had appeared by the mid-Devonian. The first real trees (e.g. Archaeopteris) had developed by the late Devonian, and the seed-bearing had evolved from the progymnosperms by the end of this geological period. The appearance of trees had a significant effect on the environment, because their advanced root systems influenced soil production and led to increased weathering.

While the earliest-known seeds date back 365 million years ago, they must have begun to evolve much earlier. Up till now, precursors of seeds were not known from the fossil record. However, a new fossil discovery, of a seed precursor with a structure seemingly involved in pollination, dates this development to at least 385 million years ago.

Reference Websites
Paleozoic Plants
This site has information & pictures of horsetails & other "fern allies": http://www.biosci.ohio-state.edu/~plantbio/greenhouse/ghconserv_tour_ferns.html

And for the clubmoss Lycopodium: http://bioweb.wku.edu/pix/plants/lycopodium.jpg

Reference Books

P. Gerrienne et al. (2004) Runcaria, a Middle Devonian seed plant precursor. Science 306: 856-858

Significance of the seed

While spores are easy to disperse, they have few reserves to establish themselves. This means that a spore reach a wet area, germinate rapidly, and begin photosynthesising straight away to gain energy for the next phase of the lifecycle. Thus spore-producing plants are limited to wet environments for at least part of their lifecycle.

In comparison, a seed contains a young plant and a nutrient store for that plant. This means that seed plants (gymnosperms and angiosperms) can colonise areas with transient or sub-surface water as the young plant can establish itself extremely rapidly once it has germinated. The evolution of the seed underpins the success of the gymnosperms and angiosperms.

In the Carboniferous (362 - 290 million years ago) conditions were warm, with little seasonal change in tropical latitudes, and the land was warm & swampy. These conditions suited the widespread forests horsetails & tree ferns that, like most other Carboniferous plants, reproduced by spores. Spores require moist conditions for germination and rapid growth. However, many of these spore-bearers died out as the environment became more arid towards the end of the Palaeozoic. The first conifers began to appear towards the end of the Carboniferous.

Reference Websites

General Information See: http://taggart.glg.msu.edu/isb200/carbfor.htm

The climate became colder and drier during the Permian (290 - 245 million years ago), with widespread glaciation in the southern hemisphere. However, plants still grew in ice-free areas, among them the Glossopteris, which is known only from Gondwanan landmasses. In fact, the distribution of Glossopteris & other members of the Glossopteridales provided early evidence of continental drift.

The seed ferns died out at the end of the Permian, and were replaced by Dicroidium and its relatives, which were also found throughout Gondwanaland. Conifers, cycads, & ginkgoes (all gymnosperms) began to replace the earlier forests, and were common across Pangaea during the Triassic (245 - 208 million years ago). New Zealand was present as largely volcanic & easily eroded islands, & was home to ferns, Dicroidium, gingkoes, and early araucarian conifers. Early podocarps may also have been present.

The appearance of flowering plants

Gymnosperms, especially the cycads, remained the dominant land plants in the Jurassic (208 - 145 million years ago), but the Cretaceous (145 - 65 million years ago) saw the rise of the flowering plants () and their associated insect pollinators (an example of ). There are around 235,000 species of angiosperms but they all share a particular set of features: flowers, fruit, and a distinctive life cycle. Because of this, angiosperms are assumed to be a monophyletic group.

The angiosperms owe their success to the evolution of the flower. The flower's pollen and nectar encourage pollinating animals to visit, increasing the odds of fertilisation by ensuring that pollen is transferred efficiently from flower to flower. (The flowers of wind-pollinated angiosperms, e.g. grasses, are very much reduced in terms of size and complexity.) After fertilisation the carpel and other parts of the flower are used to form fruit that aid dispersal of the seeds inside the fruit. In addition, the xylem of angiosperms allow very rapid movement of water through the plant. This means that flowering plants can keep their stomata open through much of the day, achieving higher photosynthetic rates than gymnosperms; this "spare" photosynthetic capacity can support the development of fruit.

Two major groups of angiosperms are the dicotyledons (more correctly, "eudicotyledons") and the monocotyledons, which include the grasses. Grasses evolved in the Eocene (56.5 - 35.4 million years ago), and this led in turn to the evolution of browsing mammals during the Oligocene (35.4 - 23.2 million years ago). As the world began to cool during the Miocene (23.2 - 5.2 million years ago) these grasslands spread and the forests contracted; by the Pliocene (5.2 - 1.6 million years ago) there were deserts in many regions. The fragmentation of forest habitats, and spread of grasslands, that accompanied this cooling trend are implicated in the evolution of humans.

The Ice Ages and New Zealand's alpine plants

The Pleistocene Ice Ages were significant in the evolution of New Zealand plants as, together with the new habitats formed by the rise of the Southern Alps, they provided the conditions for the development of our extensive endemic alpine flora.

While New Zealand has been variously forested over a long period of time, at present there are two major types of native forest: rainforest or podocarp/broadleaf forest (a mix of conifers and hardwoods), and beech forest. Other vegetation types are herb fields, grasslands, and shrub-lands, which depending on their situation can be described as coastal, lowland, or montane (alpine).

During the last glaciation, 100,000 - 10,000 years ago, mean annual temperatures dropped by 4.5oC, and the snowline lowered 830 - 850m. There was extensive glaciation along the Southern Alps, extending to sea level on much of the West Coast, and there were small glaciers on the North Island's Tararua ranges and Central Plateau. During the coldest parts of the glacial, so much water was locked up in ice that sea levels were up to 135m lower and NZ was a continuous land mass.

These extreme conditions had particularly marked effects on the evolution and distribution of New Zealand's diverse alpine flora. Prior to the Pleistocene Ice Ages, not only was the climate rather warm but also there was little high country, until the upheavals of the Kaikoura Orogeny in the late Pliocene/early Pleistocene created alpine zones. Hence our high country plants are probably of relatively recent origin (geologically speaking). Alpine plants are those found above the present tree line, but at times during glacial phases they would have extended down to the coast in much of New Zealand.

New Zealand Example
Such large-scale climatic change probably drove the evolution of New Zealand's Polystichum ferns.

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The sections included here give an overview of the history of plant and animal evolution. We have also provided information on the system used by biologists to classify living things, and included material on homologous structures, which provide evidence of evolutionary relationships.

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Lichens and moss covering rocks in Pennsylvania. Did Precambrian land look like this? Photo Credit: David Geiser, Penn State
The largest genetic study ever performed to learn when land plants and fungi first appeared on the Earth has revealed a plausible biological cause for two major climate events: the Snowball Earth eras, when ice periodically covered the globe, and the era called the Cambrian Explosion, which produced the first fossils of almost all major categories of animals living today.

According to the authors of the study, which will be published in the 10 August 2001 issue of the journal Science, plants paved the way for the evolution of land animals by simultaneously increasing the percentage of oxygen in the Earth's atmosphere and decreasing the percentage of carbon dioxide, a powerful greenhouse gas.

"Our research shows that land plants and fungi evolved much earlier than previously thought - before the Snowball Earth and Cambrian Explosion events - suggesting their presence could have had a profound effect on the climate and the evolution of life on Earth," says Blair Hedges, an evolutionary biologist and leader of the Penn State research team that performed the study.

The researchers found that land plants had evolved on Earth by about 700 million years ago and land fungi by about 1,300 million years ago - much earlier than previous estimates of around 480 million years ago, which were based on the earliest fossils of those organisms. Prior to this study, it was believed that Earth's landscape at that time was covered with barren rocks harboring nothing more than some bacteria and possibly some algae. No undisputed fossils of the earliest land plants and fungi have been found in rocks formed during the Precambrian period, says Hedges, possibly because their primitive bodies were too soft to turn into fossils.

The early appearance on the land of fungi and plants suggests their plausible role in both the mysterious lowering of the Earth's surface temperature during the series of Snowball Earth events roughly 750 million to 580 million years ago and the sudden appearance of many new species of fossil animals during the Cambrian Explosion era roughly 530 million years ago. "Both the lowering of the Earth's surface temperature and the evolution of many new types of animals could result from a decrease in atmospheric carbon dioxide and a rise in oxygen caused by the presence on land of lichen fungi and plants at this time, which our research suggests," Hedges says.

"An increase in land plant abundance may have occurred at the time just before the period known as the Cambrian Explosion, when the next Snowball Earth period failed to occur because temperatures did not get quite cold enough," Hedges says. "The plants conceivably boosted oxygen levels in the atmosphere high enough for animals to develop skeletons, grow larger, and diversify."

Lichens are believed to have been the first fungi to team up with photosynthesizing organisms like cyanobacteria and green algae. Lichens can live without rain for months, providing protection for photosynthesizing organisms, which produce oxygen and release it into the atmosphere. The researchers suggest that the pioneer lichen fungi, which produce acids strong enough to dissolve rocks, also could have helped to reduce carbon dioxide. When washed away by rainwater, the calcium released from the lichen-encrusted rocks eventually forms calcium carbonate limestone in the ocean, preventing the carbon atoms from forming the greenhouse gas, carbon dioxide, in the atmosphere.

Land plants also can lower levels of carbon dioxide in the atmosphere. They have molecules called lignins, which contain carbon but do not readily decompose. After the plant dies, some of its carbon remains locked up in the lignins and can become buried in the Earth through geologic processes, preventing those carbon atoms from returning to the atmosphere and effectively lowering atmospheric carbon dioxide.
Lichens and moss covering rocks in Pennsylvania. Photo Credit: David Geiser, Penn State
"The Earth cools when you take away carbon dioxide," Hedges says. "Other factors such as the location of the continents may have had some effect in cooling the atmosphere and creating periods of Snowball Earth, but I suspect the biggest cooling effect came from the reduction of carbon dioxide in the atmosphere by fungi and plants, which we have shown were living on the land at that time."

Fossil fuels like coal and oil are made from plant material, containing carbon that was taken out of the atmosphere and buried in swamps millions of years ago. Releasing those same carbon atoms back into the atmosphere by burning fossil fuels appears to be causing the Earth to get warmer again, according to many studies.

Hedges and his research team made their surprising discoveries about the early appearance on Earth of the first land plants and fungi by studying as many of the genes as possible of their descendants - the species of plants and fungi living today. They began by sifting through their molecular fingerprints - the unique sequences of amino-acid building blocks - in many thousands of genes from hundreds of species archived in the public gene-sequence databases.

Eventually, they found 119 genes common to living species of fungi, plants, and animals that met the researchers' stringent criteria for use as "molecular clocks." Previous studies had used a single gene. By detailed comparisons of the amino-acid sequences of individual genes among numbers of species, the scientists identified those genes that had accumulated mutations at a fairly constant rate relative to one another during their evolution. "Because mutations start occurring at regular intervals in these genes as soon as a new species evolves - like the ticking of a clock - we can use them to trace the evolutionary history of a species back to its time of origin," Hedges explains.

The scientists calibrated each of their gene clocks with evolutionary events well established by fossil studies, primarily those in the history of animals. Using these known dates as secure calibration points, and the mutation rate for each of the constant-rate genes as a timing device, the researchers were able to determine how long ago each of the species originated.

Hedges says his research might help in the search for life on other planets by providing a link between the different stages of life's evolution on Earth and the timing of events in the chemical evolution of Earth's atmosphere, such as the rise in oxygen. "Possibly the early history of life on Earth can give us clues for predicting the kinds of lifeforms that are likely to exist on planets in other solar systems from the chemical content of their atmospheres," Hedges says.

In addition to Hedges, the Penn State research team includes Daniel S. Heckman, an undergraduate student whose senior honors thesis formed part of this research; David M. Geiser, assistant professor of plant pathology; and undergraduate students Brooke R. Eidell; Rebecca L. Stauffer; and Natalie L. Kardos. This research was supported, in part, by the National Aeronautics and Space Administration through the Penn State Astrobiology Research Center.

CONTACT:

Blair Hedges, 814-865-9991, sbh1@psu.edu
Barbara K. Kennedy, 814-863-4682, science@psu.edu

IMAGES:

Additional high-quality color images of lichen are available directly from Stephen Sharnoff, a professional photographer and colleague of the researchers, via e-mail at lichen@idiom.com, telephone at 510-548-9189, or postal service at 2406 Roosevelt Ave., Berkeley, CA 94703.

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First Land Plants and Fungi Changed Earth's Climate, Paving the Way for Explosive Evolution of Land Animals, New Gene Study Suggests

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Lichens and moss covering rocks in Pennsylvania. Did Precambrian land look like this? Photo Credit: David Geiser, Penn State The largest genetic study ever performed to learn when land plants and fungi first appeared on the Earth has revealed a plausible biological cause for two major climate events: the Snowball Earth eras, when ice periodically covered the globe, and the era called the Cambrian Explosion, which produced the first fossils of almost all major categories of animals living today.

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WELCOME TO THE WORLD OF We’re on a mission to share the beauty and intelligence of nature – starting with the magic and mystery of mushrooms – to protect the planet and create a better future.

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Chapter 14: Diversity of Plants

Learning Objectives

By the end of this section, you will be able to:

Describe the major characteristics of the plant kingdom

Discuss the challenges to plant life on land

Describe the adaptations that allowed plants to colonize land

Plants are a large and varied group of organisms. There are close to 300,000 species of catalogued plants. Of these, about 260,000 are plants that produce seeds. Mosses, ferns, conifers, and flowering plants are all members of the plant kingdom. The plant kingdom contains mostly photosynthetic organisms; a few parasitic forms have lost the ability to photosynthesize. The process of photosynthesis uses chlorophyll, which is located in organelles called chloroplasts. Plants possess cell walls containing cellulose. Most plants reproduce sexually, but they also have diverse methods of asexual reproduction. Plants exhibit indeterminate growth, meaning they do not have a final body form, but continue to grow body mass until they die.

As organisms adapt to life on land, they have to contend with several challenges in the terrestrial environment. Water has been described as "the stuff of life." The cell's interior-the medium in which most small molecules dissolve and diffuse, and in which the majority of the chemical reactions of metabolism take place-is a watery soup. Desiccation, or drying out, is a constant danger for an organism exposed to air. Even when parts of a plant are close to a source of water, their aerial structures are likely to dry out. Water provides buoyancy to organisms that live in aquatic habitats. On land, plants need to develop structural support in air-a medium that does not give the same lift. Additionally, the male gametes must reach the female gametes using new strategies because swimming is no longer possible. Finally, both gametes and zygotes must be protected from drying out. The successful land plants evolved strategies to deal with all of these challenges, although not all adaptations appeared at once. Some species did not move far from an aquatic environment, whereas others left the water and went on to conquer the driest environments on Earth.

To balance these survival challenges, life on land offers several advantages. First, sunlight is abundant. On land, the spectral quality of light absorbed by the photosynthetic pigment, chlorophyll, is not filtered out by water or competing photosynthetic species in the water column above. Second, carbon dioxide is more readily available because its concentration is higher in air than in water. Additionally, land plants evolved before land animals; therefore, until dry land was colonized by animals, no predators threatened the well-being of plants. This situation changed as animals emerged from the water and found abundant sources of nutrients in the established flora. In turn, plants evolved strategies to deter predation: from spines and thorns to toxic chemicals.

The early land plants, like the early land animals, did not live far from an abundant source of water and developed survival strategies to combat dryness. One of these strategies is drought tolerance. Mosses, for example, can dry out to a brown and brittle mat, but as soon as rain makes water available, mosses will soak it up and regain their healthy, green appearance. Another strategy is to colonize environments with high humidity where droughts are uncommon. Ferns, an early lineage of plants, thrive in damp and cool places, such as the understory of temperate forests. Later, plants moved away from aquatic environments using resistance to desiccation, rather than tolerance. These plants, like the cactus, minimize water loss to such an extent they can survive in the driest environments on Earth.

In addition to adaptations specific to life on land, land plants exhibit adaptations that were responsible for their diversity and predominance in terrestrial ecosystems. Four major adaptations are found in many terrestrial plants: the alternation of generations, a sporangium in which spores are formed, a gametangium that produces haploid cells, and in vascular plants, apical meristem tissue in roots and shoots.

Alternation of Generations

Alternation of generations describes a life cycle in which an organism has both haploid and diploid multicellular stages ([Figure 1]).

Haplontic refers to a life cycle in which there is a dominant haploid stage. Diplontic refers to a life cycle in which the diploid stage is the dominant stage, and the haploid chromosome number is only seen for a brief time in the life cycle during sexual reproduction. Humans are diplontic, for example. Most plants exhibit alternation of generations, which is described as haplodiplontic: the haploid multicellular form known as a gametophyte is followed in the development sequence by a multicellular diploid organism, the sporophyte. The gametophyte gives rise to the gametes, or reproductive cells, by mitosis. It can be the most obvious phase of the life cycle of the plant, as in the mosses, or it can occur in a microscopic structure, such as a pollen grain in the higher plants (the collective term for the vascular plants). The sporophyte stage is barely noticeable in lower plants (the collective term for the plant groups of mosses, liverworts, and hornworts). Towering trees are the diplontic phase in the lifecycles of plants such as sequoias and pines.

Sporangia in the Seedless Plants

The sporophyte of seedless plants is diploid and results from syngamy or the fusion of two gametes ([Figure 1]). The sporophyte bears the sporangia (singular, sporangium), organs that first appeared in the land plants. The term "sporangia" literally means "spore in a vessel," as it is a reproductive sac that contains spores. Inside the multicellular sporangia, the diploid sporocytes, or mother cells, produce haploid spores by meiosis, which reduces the 2 n chromosome number to 1 n. The spores are later released by the sporangia and disperse in the environment. Two different types of spores are produced in land plants, resulting in the separation of sexes at different points in the life cycle. Seedless nonvascular plants (more appropriately referred to as "seedless nonvascular plants with a dominant gametophyte phase") produce only one kind of spore, and are called homosporous. After germinating from a spore, the gametophyte produces both male and female gametangia, usually on the same individual. In contrast, heterosporous plants produce two morphologically different types of spores. The male spores are called microspores because of their smaller size; the comparatively larger megaspores will develop into the female gametophyte. Heterospory is observed in a few seedless vascular plants and in all seed plants.

When the haploid spore germinates, it generates a multicellular gametophyte by mitosis. The gametophyte supports the zygote formed from the fusion of gametes and the resulting young sporophyte or vegetative form, and the cycle begins anew ([Figure 2] and [Figure 3]).

The spores of seedless plants and the pollen of seed plants are surrounded by thick cell walls containing a tough polymer known as sporopollenin. This substance is characterized by long chains of organic molecules related to fatty acids and carotenoids, and gives most pollen its yellow color. Sporopollenin is unusually resistant to chemical and biological degradation. Its toughness explains the existence of well-preserved fossils of pollen. Sporopollenin was once thought to be an innovation of land plants; however, the green algae Coleochaetes is now known to form spores that contain sporopollenin.

Protection of the embryo is a major requirement for land plants. The vulnerable embryo must be sheltered from desiccation and other environmental hazards. In both seedless and seed plants, the female gametophyte provides nutrition, and in seed plants, the embryo is also protected as it develops into the new generation of sporophyte.

Gametangia in the Seedless Plants

Gametangia (singular, gametangium) are structures on the gametophytes of seedless plants in which gametes are produced by mitosis. The male gametangium, the antheridium, releases sperm. Many seedless plants produce sperm equipped with flagella that enable them to swim in a moist environment to the archegonia, the female gametangium. The embryo develops inside the archegonium as the sporophyte.

Apical Meristems

The shoots and roots of plants increase in length through rapid cell division within a tissue called the apical meristem ([Figure 4]). The apical meristem is a cap of cells at the shoot tip or root tip made of undifferentiated cells that continue to proliferate throughout the life of the plant. Meristematic cells give rise to all the specialized tissues of the plant. Elongation of the shoots and roots allows a plant to access additional space and resources: light in the case of the shoot, and water and minerals in the case of roots. A separate meristem, called the lateral meristem, produces cells that increase the diameter of stems and tree trunks. Apical meristems are an adaptation to allow vascular plants to grow in directions essential to their survival: upward to greater availability of sunlight, and downward into the soil to obtain water and essential minerals.

As plants adapted to dry land and became independent of the constant presence of water in damp habitats, new organs and structures made their appearance. Early land plants did not grow above a few inches off the ground, and on these low mats, they competed for light. By evolving a shoot and growing taller, individual plants captured more light. Because air offers substantially less support than water, land plants incorporated more rigid molecules in their stems (and later, tree trunks). The evolution of vascular tissue for the distribution of water and solutes was a necessary prerequisite for plants to evolve larger bodies. The vascular system contains xylem and phloem tissues. Xylem conducts water and minerals taken from the soil up to the shoot; phloem transports food derived from photosynthesis throughout the entire plant. The root system that evolved to take up water and minerals also anchored the increasingly taller shoot in the soil.

In land plants, a waxy, waterproof cover called a cuticle coats the aerial parts of the plant: leaves and stems. The cuticle also prevents intake of carbon dioxide needed for the synthesis of carbohydrates through photosynthesis. Stomata, or pores, that open and close to regulate traffic of gases and water vapor therefore appeared in plants as they moved into drier habitats.

Plants cannot avoid predatory animals. Instead, they synthesize a large range of poisonous secondary metabolites: complex organic molecules such as alkaloids, whose noxious smells and unpleasant taste deter animals. These toxic compounds can cause severe diseases and even death.

Additionally, as plants coevolved with animals, sweet and nutritious metabolites were developed to lure animals into providing valuable assistance in dispersing pollen grains, fruit, or seeds. Plants have been coevolving with animal associates for hundreds of millions of years ([Figure 5]).

Land plants are classified into two major groups according to the absence or presence of vascular tissue, as detailed in [Figure 7]. Plants that lack vascular tissue formed of specialized cells for the transport of water and nutrients are referred to as nonvascular plants. The bryophytes, liverworts, mosses, and hornworts are seedless and nonvascular, and likely appeared early in land plant evolution. Vascular plants developed a network of cells that conduct water and solutes through the plant body. The first vascular plants appeared in the late Ordovician (461-444 million years ago) and were probably similar to lycophytes, which include club mosses (not to be confused with the mosses) and the pterophytes (ferns, horsetails, and whisk ferns). Lycophytes and pterophytes are referred to as seedless vascular plants. They do not produce seeds, which are embryos with their stored food reserves protected by a hard casing. The seed plants form the largest group of all existing plants and, hence, dominate the landscape. Seed plants include gymnosperms, most notably conifers, which produce "naked seeds," and the most successful plants, the flowering plants, or angiosperms, which protect their seeds inside chambers at the center of a flower. The walls of these chambers later develop into fruits.

Land plants evolved traits that made it possible to colonize land and survive out of water. Adaptations to life on land include vascular tissues, roots, leaves, waxy cuticles, and a tough outer layer that protects the spores. Land plants include nonvascular plants and vascular plants. Vascular plants, which include seedless plants and plants with seeds, have apical meristems, and embryos with nutritional stores. All land plants share the following characteristics: alternation of generations, with the haploid plant called a gametophyte and the diploid plant called a sporophyte; formation of haploid spores in a sporangium; and formation of gametes in a gametangium.

The land plants are probably descendants of which of these groups?

[reveal-answer q="675979″]Show Answer[/reveal-answer]
[hidden-answer a="675979″]1[/hidden-answer]

The event that leads from the haploid stage to the diploid stage in alternation of generations is ________.

[reveal-answer q="944729″]Show Answer[/reveal-answer]
[hidden-answer a="944729″]3[/hidden-answer]

Moss is an example of which type of plant?

1. haplontic plant

2. vascular plant

3. diplontic plant

4. seed plant

[reveal-answer q="801206″]Show Answer[/reveal-answer]
[hidden-answer a="801206″]1[/hidden-answer]

What adaptations do plants have that allow them to survive on land?

The sporangium of plants protects the spores from drying out. Apical meristems ensure that a plant is able to grow in the two directions required to acquire water and nutrients: up toward sunlight and down into the soil. The multicellular embryo is an important adaptation that improves survival of the developing plant in dry environments. The development of molecules that gave plants structural strength allowed them to grow higher on land and obtain more sunlight. A waxy cuticle prevents water loss from aerial surfaces.

Footnotes

A.D. Chapman (2009) Numbers of Living Species in Australia and the World. 2nd edition. A Report for the Australian Biological Resources Study. Australian Biodiversity Information Services, Toowoomba, Australia. Available online at http://www.environment.gov.au/biodiversity/abrs/publications/other/species-numbers/2009/04-03-groups-plants.html.

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Chapter 14: Diversity of Plants By the end of this section, you will be able to: Describe the major characteristics of the plant kingdom Discuss the challenges to plant life on land Describe the adaptations that allowed plants to colonize land Plants are a large and varied group of organisms. There are close to 300,000 species of catalogued plants.

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Scientists group organisms, or living things, with similar traits together. Kingdoms are the largest group, and there are five of them: plant, animal, fungus, protist, and bacteria. Grouping organisms into kingdoms helps scientists understand similarities among living things.

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Animals: The Kingdoms of Life: StudyJams! Science | Scholastic.com

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All living things fall into one of five kingdoms. In this activity, students will learn about the kingdoms of life and group animals of similar traits together.

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Watch the animation to find out how protists, which are single-cell organisms that are neither animal nor plant, function.

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Protists | UNC-TV Science | PBS LearningMedia

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Watch the animation to find out how protists, which are single-cell organisms that are neither animal nor plant, function.

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A book about protists.

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Instantly access over 40,000 of the best books & videos for kids on Epic

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Get unlimited access to 40,000 of the best books, audiobooks, videos, & more for kids 12 and under. Try it free.

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Animals: Mammals, Birds, Reptiles, Amphibians, Fish and other Animals

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Animals: Mammals, Birds, Reptiles, Amphibians, Fish and other Animals

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A book about animals.

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Instantly access over 40,000 of the best books & videos for kids on Epic

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Get unlimited access to 40,000 of the best books, audiobooks, videos, & more for kids 12 and under. Try it free.

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The Green Algae - Chlorophyta Photosynthetic aquatic organisms that do not have vascular tissues are
commonly called algae. Review: In plants, conducting tissues and associated supportive fibres are
called the vascular tissues. Xylem tissue transports water and dissolved minerals to
t…

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Dippy the Dinosaur in Norwich: The Evolution of Land Plants 🌿

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Exploring the Plant Kingdom - Lesson Plan

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They may have looked more like a green carpet than a forest but the first land plants really did change the world.

New research led by scientists from Oxford University and Exeter University has shown that the invasion of the land by plants in the Ordovician Period (488-443 million years ago) cooled the climate and triggered a series of ice ages.

I asked Liam Dolan of Oxford University's Department of Plant Sciences, one of the leaders of the research reported today in Nature Geoscience, about the work and what it reveals about yesterday's - and tomorrow's - climate:

OxSciBlog: What sort of plants were there during the Ordovician?
Liam Dolan: The fossil record tells us that the first plants to grow on land appeared sometime before 475 million years ago during the Ordovician Period.

We only have fossilised remains of small fragments of plants but we don't know how the bits fit together - a bit like a jigsaw puzzle with a lot of the bits missing. It is safe to say that these plants were very small and probably looked like liverworts and mosses - their closest living relatives.

OSB: How did the climate change during this period?
LD: Climate changed dramatically during the late Ordovician Period. It changed from a climate that was warmer than today (with no ice) into an ice age. Ice ages are pretty rare in Earth history and what gave rise to the Ordovician glaciation has always been a mystery.

OSB: How did you test whether plants triggered this change?
LD: While increasing the amount of carbon dioxide causes global warming, removing carbon dioxide from the atmosphere causes global cooling. One of the dominant mechanisms for removing carbon dioxide from the atmosphere is silicate weathering: the chemical reaction between silicate minerals of rocks and carbon dioxide in the atmosphere.

We tested the hypothesis that non-vascular plants (mosses) increase rates of silicate weathering. To our amazement we found that these simple plants did in fact increase the weathering of silicate minerals. We then incorporated these measurements of silicate weathering rates into computer models of Ordovician Period climate.

When we re-ran the models with our new data, we discovered that the appearance of the first land plants in the Ordovician plants would have caused a dramatic decrease in atmospheric carbon dioxide which would have brought about climate cooling and contributed to the initiation of the late Ordovician ice age.

OSB: What do your results reveal about how plants influence climate?
LD: We know that plants play a critical role in climate systems by pulling carbon dioxide out of the atmosphere in two ways: Firstly, plants carry out photosynthesis, which converts carbon dioxide into plant biomass that store carbon. Secondly, plants increase rates of silicate weathering, the chemical reaction that breaks down rocks, and in so doing removes carbon dioxide from the atmosphere.

We knew that the dramatic cooling of the planet between 300 and 200 million years ago was the result of the evolution of large plants with large rooting systems that caused huge changes in both of these processes. In the results we published today we showed that the appearance of the first land plants had an effect much earlier - 100 million years earlier.

For me the most important take home message is that the invasion of the land by plants - a pivotal time in the history of the planet - brought about huge climate changes. It should also remind us that the removal of large areas of the world's vegetation, which act as carbon stores, will increase atmospheric carbon dioxide levels and cause dramatic climate change.

OSB: What can they tell us about plants and climate change today?
LD: Our discovery emphasizes that plants have a central regulatory role in the control of climate: they did yesterday, they do today and they certainly will in the future. This study warns us that if we continue destroy the Earth's vegetation, by felling forests and draining wet lands, we will suffer dramatic climate change: the opposite of an ice-age. That's called global warming.
Professor Liam Dolan is based at Oxford's Department of Plant Sciences.

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They may have looked more like a green carpet than a forest but the first land plants really did change the world. New research led by scientists from Oxford University and Exeter University has shown that the invasion of the land by plants in the Ordovician Period (488-443 million years ago) cooled the climate and triggered a series of ice ages.

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How a Mass Extinction Event Created the Amazon

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How a mass extinction event created the Amazon 

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How a mass extinction event created the Amazon 

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How a Mass Extinction Event Created the Amazon

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Precambrian Creatures: The First Animals

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Precambrian Creatures: The First Animals

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The Phanerozoic eon is the current eon on the geologic timescale. It is the one in which abundant animal life has existed. It covers about 541 million years, and goes back to the time when hard-shelled animals first appeared. It was once thought that life began in the Cambrian, the first period of this eon.

The time before the Phanerozoic, formerly called the Precambrian, is now divided into the Hadean, Archaean and Proterozoic eons.

Eras of the Phanerozoic

The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic, which are further subdivided into 12 periods. The Paleozoic features the rise of fish, amphibians and reptiles. The Mesozoic is ruled by the reptiles, and features the evolution of mammals, and more famously, dinosaurs, including birds. The Cenozoic is the time of the mammals, and more recently, humans.

Paleozoic Era

The Paleozoic is a time in Earth's history when complex life forms evolved, took their first breath of oxygen on dry land, and when the forerunners of all life on Earth began to diversify. There are six periods in the Paleozoic era: Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian.

Cambrian Period

The Cambrian is the first period of the Paleozoic Era and starts from 541 to 485 million years ago. The Cambrian sparked a rapid expansion in evolution in an event known as the Cambrian Explosion during which the greatest number of creatures evolved in a single period in the history of Earth. Plants like algae evolved, and the fauna was dominated by armored arthropods, such as trilobites. Almost all marine phyla evolved in this period. During this time, the super-continent Pannotia began to break up, most of which later recombined into the super-continent Gondwana.

Ordovician Period

The Ordovician spans from 485 million years to 444 million years ago. The Ordovician was a time in Earth's history in which many species still prevalent today evolved, such as primitive fish, cephalopods, and coral. The most common forms of life, however, were trilobites, snails and shellfish. More importantly, the first arthropods crept ashore to colonize Gondwana, a continent empty of animal life. By the end of the Ordovician, Gondwana had moved from the equator to the South Pole, and Laurentia had collided with Baltica, closing the Iapetus Ocean. The glaciation of Gondwana resulted in a major drop in sea level, killing off all life that had established along its coast. Glaciation caused a snowball Earth, leading to the Ordovician-Silurian extinction, during which 60% of marine invertebrates and 25% of families became extinct. This is considered the first mass extinction and the second deadliest in the history of Earth.

Silurian Period

The Silurian spans from 444 million years to 419 million years ago, which saw a warming from Snowball Earth. This period saw the mass evolution of fish, as jaw-less fish became more numerous, jawed fish evolved, and the first freshwater fish evolved, though arthropods, such as sea scorpions, remained the apex predators. Fully terrestrial life evolved, which included early arachnids, fungi, and centipedes. The evolution of vascular plants (Cooksonia) allowed plants to gain a foothold on land. These early terrestrial plants are the forerunners of all plant life on land. During this time, there were four continents: Gondwana (Africa, South America, Australia, Antarctica, India), Laurentia (North America with parts of Europe), Baltica (the rest of Europe), and Siberia (Northern Asia). The recent rise in sea levels provided new habitats for many new species.

Devonian Period

The Devonian spans from 419 million years to 359 million years ago. Also informally known as the "Age of the Fish", the Devonian features a huge diversification in fish, including armored fish like Dunkleosteus and lobe-finned fish which eventually evolved into the first tetrapods. On land, plant groups diversified; the first trees and seeds evolved. By the Middle Devonian, shrub-like forests of primitive plants existed: lycophytes, horsetails, ferns, and progymnosperm. This event also allowed the diversification of arthropod life as they took advantage of the new habitat. The first amphibians also evolved, and the fish were now at the top of the food chain. Near the end of the Devonian, 70% of all species became extinct in an event known as the Late Devonian extinction, which is the second mass extinction known to have happened.

Carboniferous Period

The Carboniferous spans from 359 million to 299 million years ago. During this period, average global temperatures were exceedingly high: the early Carboniferous averaged at about 20 degrees Celsius (but cooled to 10 degrees during the Middle Carboniferous). Tropical swamps dominated the Earth, and the large amounts of trees created much of the carbon that became coal deposits (hence the name Carboniferous). The high oxygen levels caused by these swamps allowed massive arthropods, normally limited in size by their respiratory systems, to proliferate. Perhaps the most important evolutionary development of the time was the evolution of amniotic eggs, which allowed amphibians to move farther inland and remain the dominant vertebrates throughout the period. Also, the first reptiles and synapsids evolved in the swamps. Throughout the Carboniferous, there was a cooling pattern, which eventually led to the glaciation of Gondwana as much of it was situated around the south pole, in an event known as the Permo-Carboniferous glaciation or the Carboniferous Rainforest Collapse.

Permian Period

The Permian spans from 299 million to 252 million years ago and was the last period of the Paleozoic Era. At its beginning, all continents came together to form the super-continent Pangaea, surrounded by one ocean called Panthalassa. The Earth was very dry during this time, with harsh seasons, as the climate of the interior of Pangaea wasn't regulated by large bodies of water. Reptiles and synapsids flourished in the new dry climate. Creatures such as Dimetrodon and Edaphosaurus ruled the new continent. The first conifers evolved, then dominated the terrestrial landscape. Nearing the end of the period, Scutosaurus and gorgonopsids filled the arid landmass. Eventually, they disappeared, along with 95% of all life on Earth in an event simply known as " the Great Dying", the world's third mass extinction event and the largest in its history.

Mesozoic Era

The Mesozoic ranges from 252 million to 66 million years ago. Also known as "the Age of the dinosaurs", the Mesozoic features the rise of reptiles on their 150 million year conquest of the Earth on the land, in the seas, and in the air. There are three periods in the Mesozoic: Triassic, Jurassic, and Cretaceous.

Triassic Period

The Triassic ranges from 252 million to 201 million years ago. The Triassic is a transitional time in Earth's history between the Permian Extinction and the lush Jurassic Period. It has three major epochs: Early Triassic, Middle Triassic and Late Triassic.

The Early Triassic lasted between 252 million to 247 million years ago, and was dominated by deserts as Pangaea had not yet broken up, thus the interior was arid. The Earth had just witnessed a massive die-off in which 95% of all life became extinct. The most common life on Earth were Lystrosaurus, labyrinthodonts, and Euparkeria along with many other creatures that managed to survive the Great Dying. Temnospondyli flourished during this time and were dominant predators for much of the Triassic.

The Middle Triassic spans from 247 million to 237 million years ago. The Middle Triassic featured the beginnings of the breakup of Pangaea, and the beginning of the Tethys Sea. The ecosystem had recovered from the devastation of the Great Dying. Phytoplankton, coral, and crustaceans all had recovered, and the reptiles began increasing in size. New aquatic reptiles, such as ichthyosaurs and nothosaurs, proliferated in the seas. Meanwhile, on land, pine forests flourished, as well as mosquitoes and fruit flies. The first ancient crocodilians evolved, which sparked competition with the large amphibians that had long ruled the freshwater world.

The Late Triassic spans from 237 million to 201 million years ago. Following the bloom of the Middle Triassic, the Late Triassic featured frequent rises of temperature, as well as moderate precipitation (10-20 inches per year). The recent warming led to a boom of reptilian evolution on land as the first true dinosaurs evolved, as well as pterosaurs. By the end of the period the first gigantic dinosaurs had evolved and advanced pterosaurs colonised Pangaea's deserts. The climactic change, however, resulted in a large die-out known as the Triassic-Jurassic extinction event, in which all archosaurs (excluding ancient crocodiles and dinosaurs), most synapsids, and almost all large amphibians became extinct, as well as 34% of marine life in the fourth mass extinction event. The extinction's cause is debated.

Jurassic Period

The Jurassic ranges from 201 million to 145 million years ago, and features three major epochs: Early Jurassic, Middle Jurassic, and Late Jurassic.

The Early Jurassic Epoch spans from 201 million to 174 million years ago. The climate was much more humid than the Triassic, and as a result, the world was very tropical. In the oceans, plesiosaurs, ichthyosaurs and ammonites dominated the seas. On land, dinosaurs and other reptiles dominated the land, with species such as Dilophosaurus at the apex. The first true crocodiles evolved, pushing the large amphibians to near extinction. The reptiles rose to rule the world. Meanwhile, the first true mammals evolved, but never exceeded the height of a shrew.

The Middle Jurassic Epoch spans from 174 million to 163 million years ago. During this epoch, dinosaurs flourished as huge herds of sauropods, such as Brachiosaurus and Diplodocus, filled the fern prairies of the Middle Jurassic. Many other predators rose as well, such as Allosaurus. Conifer forests made up a large portion of the world's forests. In the oceans, plesiosaurs were quite common, and ichthyosaurs were flourishing. This epoch was the peak of the reptiles.

The Late Jurassic Epoch spans from 163 million to 145 million years ago. The Late Jurassic featured a massive extinction of sauropods and ichthyosaurs due to the separation of Pangaea into Laurasia and Gondwana in an extinction known as the Jurassic-Cretaceous extinction. Sea levels rose, destroying fern prairies and creating shallows. Ichthyosaurs became extinct whereas sauropods, as a whole, did not; in fact, some species, like Titanosaurus, lived until the K-T extinction. The increase in sea-levels opened up the Atlantic sea way which would continue to get larger over time. The divided world would give opportunity for the diversification of new dinosaurs.

Cretaceous Period

The Cretaceous is the longest period in the Mesozoic, spans from 145 million to 66 million years ago, and is divided into two epochs: Early Cretaceous, and Late Cretaceous.

The Early Cretaceous Epoch spans from 145 million to 100 million years ago. The Early Cretaceous saw the expansion of seaways, and as a result, the decline and extinction of sauropods (except in South America). Many coastal shallows were created, and that caused ichthyosaurs to die out. Mosasaurs evolved to replace them as apex species of the seas. Some island-hopping dinosaurs, like Eustreptospondylus, evolved to cope with the coastal shallows and small islands of ancient Europe. Other dinosaurs, such as Carcharodontosaurus and Spinosaurus, rose to fill the empty space that the Jurassic-Cretaceous extinction had created. Of the most successful would be the which spread to every continent. Seasons came back into effect and the poles grew seasonally colder. Dinosaurs such as the Leaellynasaura inhabited the polar forests year-round, while many dinosaurs, such as the Muttaburrasaurus, migrated there during summer . Since it was too cold for crocodiles, it was the last stronghold for large amphibians, such as the Koolasuchus. In this epoch Pterosaurs reached their maximum diversity and grew larger, as species like Tapejara and Ornithocheirus took to the skies. The first true birds evolved, possibly sparking competition between them and the pterosaurs.

The Late Cretaceous Epoch spans from 100 million to 66 million years ago. The Late Cretaceous featured a cooling trend that would continue into the Cenozoic Era. Eventually, tropical ecology was restricted to the equator and areas beyond the tropic lines featured extreme seasonal changes of weather. Dinosaurs still thrived as new species such as Tyrannosaurus, Ankylosaurus, Triceratops and Hadrosaurs dominated the food web. Whether or not Pterosaurs went into a decline as birds radiated is debated, however many families survived until the end of the Cretaceous, alongside new species such as the gigantic Quetzalcoatlus. Marsupials evolved within the large conifer forests as scavengers. In the oceans, Mosasaurs ruled the seas to fill the role of the ichthyosaurs, and huge plesiosaurs, such as Elasmosaurus, evolved. Also, the first flowering plants evolved. At the end of the Cretaceous, the Deccan Traps and other volcanic eruptions were poisoning the atmosphere. As this was continued, it is thought that a large meteor smashed into Earth, creating the Chicxulub Crater creating the event known as the K-T Extinction, the fifth and most recent mass extinction event, during which 75% of life on Earth became extinct, including all non-avian dinosaurs. Every living thing with a body mass over 10 kilograms became extinct, and the age of the dinosaurs came to an end.

Cenozoic Era

The Cenozoic featured the rise of mammals as the dominant class of animals, as the end of the age of the dinosaurs left significant evolutionary vacuums. There are three divisions of the Cenozoic: Paleogene, Neogene and Quaternary.

Paleogene Period

The Paleogene spans from the extinction of the non-avian dinosaurs, some 66 million years ago, to the dawn of the Neogene 23 million years ago. It features three epochs: Paleocene, Eocene and Oligocene.

The Paleocene Epoch began with the K-T extinction event caused by the impact of a meteorite in the area of present-day Yucatan Peninsula and caused the destruction of 75% of all species on Earth. The Early Paleocene saw the recovery of the Earth from that event. The continents began to take their modern shape, but all continents (and India) were separated from each other. Afro-Eurasia was separated by the Tethys Sea, and the Americas were separated by the strait of Panama, as the Isthmus of Panama had not yet formed. This epoch featured a general warming trend, and jungles eventually reached the poles. The oceans were dominated by sharks as the large reptiles that had once ruled became extinct. Archaic mammals, such as creodonts and early primates that evolved during the Mesozoic filled the world. Mammals were still quite small, meanwhile enormous crocodiles and snakes like radiated to fill the niche of top predator.

The Eocene Epoch ranged from 56 million to 34 million years ago. In the early Eocene, most land mammals were small and living in cramped jungles, much like the Paleocene. Among them were early primates, whales and horses along with many other early forms of mammals. At the top of the food chains were huge birds, such as . Carnivorous flightless birds continued to be top predators for much of the rest of the Cenozoic, until their extinction in the Quaternary period. The temperature was 30 degrees Celsius with little temperature gradient from pole to pole. In the Middle Eocene Epoch, the circum-Antarctic current between Australia and Antarctica formed which disrupted ocean currents worldwide, resulting in global cooling, and caused the jungles to shrink. This allowed mammals to grow; some such as whales to mammoth proportions, which were, by now, almost fully aquatic. Mammals like Andrewsarchus were now at the top of the food-chain and sharks were replaced by Basilosaurus, whales, as rulers of the seas. The late Eocene Epoch saw the rebirth of seasons, which caused the expansion of savanna-like areas, along with the evolution of grass. At the transition between the Eocene and Oligocene epochs there was a significant extinction event, the cause of which is debated.

The Oligocene Epoch spans from 34 million to 23 million years ago. The Oligocene was an important transitional period between the tropical world of the Eocene and more modern ecosystems. This period featured a global expansion of grass which had led to many new species to take advantage, including the first elephants, cats, dogs, marsupials and many other species still prevalent today. Many other species of plants evolved during this epoch also, such as the evergreen trees. The long term cooling continued and seasonal rains patterns established. Mammals continued to grow larger. Paraceratherium, the largest land mammal to ever live evolved during this epoch, along with many other perissodactyls.

Neogene Period

The Neogene spans from 23.03 million to 2.58 million years ago. It features 2 epochs: the Miocene, and the Pliocene.

The Miocene spans from 23.03 to 5.333 million years ago and is a period in which grass spread further across, effectively dominating a large portion of the world, diminishing forests in the process. Kelp forests evolved, leading to the evolution of new species, such as sea otters. During this time, perissodactyla thrived, and evolved into many different varieties. Alongside them were the apes, which evolved into a 30 species. Overall, arid and mountainous land dominated most of the world, as did grazers. The Tethys Sea finally closed with the creation of the Arabian Peninsula and in its wake left the Black, Red, Mediterranean and Caspian Seas. This only increased aridity. Many new plants evolved, and 95% of modern seed plants evolved in the mid-Miocene.

The Pliocene lasted from 5.333 to 2.58 million years ago. The Pliocene featured dramatic climactic changes, which ultimately led to modern species and plants. The Mediterranean Sea dried up for several thousand years in the Messinian salinity crisis. Along with these major geological events, Australopithecus evolved in Africa, beginning the human branch. The isthmus of Panama formed, and animals migrated between North and South America, wreaking havoc on the local ecology. Climatic changes brought savannas that are still continuing to spread across the world, Indian monsoons, deserts in East Asia, and the beginnings of the Sahara desert. The Earth's continents and seas moved into their present shapes. The world map has not changed much since, save for changes brought about by the glaciations of the Quaternary, such as the Great Lakes.

Quaternary Period

The Quaternary spans from 2.58 million years ago to present day, and is the shortest geological period in the Phanerozoic Eon. It features modern animals, and dramatic changes in the climate. It is divided into two epochs: the Pleistocene and the Holocene.

The Pleistocene lasted from 2.58 million to 11,700 years ago. This epoch was marked by ice ages as a result of the cooling trend that started in the Mid-Eocene. There were at least four separate glaciation periods marked by the advance of ice caps as far south as 40 degrees N latitude in mountainous areas. Meanwhile, Africa experienced a trend of desiccation which resulted in the creation of the Sahara, Namib, and Kalahari deserts. Many animals evolved including mammoths, giant ground sloths, dire wolves, saber-toothed cats, and most famously Homo sapiens. 100,000 years ago marked the end of one of the worst droughts of Africa, and led to the expansion of primitive human. As the Pleistocene drew to a close, a major extinction wiped out much of the world's megafauna, including some of the hominid species, such as Neanderthals. All the continents were affected, but Africa to a lesser extent. That continent retains many large animals, such as hippos. The extent to which Homo Sapiens were involved in this extinction is debated.

The Holocene began 11,700 years ago and lasts until to present day. All recorded history and "the history of the world" lies within the boundaries of the Holocene epoch. Human activity is blamed for a mass extinction that began roughly 10,000 years ago, though the species becoming extinct have only been recorded since the Industrial Revolution. This is sometimes referred to as the " Sixth Extinction". More than 322 species have become extinct due to human activity since the Industrial Revolution.

Biodiversity

It has been demonstrated that changes in biodiversity through the Phanerozoic correlate much better with the hyperbolic model (widely used in demography and macrosociology) than with exponential and logistic models (traditionally used in population biology and extensively applied to fossil biodiversity as well). The latter models imply that changes in diversity are guided by a first-order positive feedback (more ancestors, more descendants) or a negative feedback that arises from resource limitation, or both. The hyperbolic model implies a second-order positive feedback. The hyperbolic pattern of the human population growth arises from a second-order positive feedback, caused by the interaction of the population size and the rate of technological growth. The character of biodiversity growth in the Phanerozoic Eon can be similarly accounted for by a feedback between the diversity and community structure complexity. It is suggested that the similarity between the curves of biodiversity and human population probably comes from the fact that both are derived from the superposition on the hyperbolic trend of cyclical and random dynamics.

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The Phanerozoic eon is the current eon on the geologic timescale. It is the one in which abundant animal life has existed. It covers about 541 million years, and goes back to the time when hard-shelled animals first appeared. It was once thought that life began in the Cambrian, the first period of this eon.

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The Cambrian Period: Life's Prototype Stage | Random Thursday

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Creatures of the Cambrian - Tour Through Time Episode 1

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What is biodiversity?

Biodiversity refers to the variety and variability of all life on earth. Due to the process of evolution, thousands of species of animals and plants now exist on the planet. Biodiversity encompasses the wide range of genes, species, and ecosystems that have become established on the planet, which intertwines and impact each other.

Image Credit: Ethan Daniels/Shutterstock.com

A multitude of factors impacts biodiversity, and scientists are interested in controlling these factors to prevent the reduction of natural biodiversity due to human interference.

Without biodiversity, day to day life would look completely different for humans. We rely on roughly 40,000 species every day, mostly without noticing. Our food, water, oxygen, and energy supplies all depend on biodiversity.

Medicine, the earth's climate, and waste detoxification too all rely on maintaining biodiversity. For this reason, it is of paramount importance that we understand how human activity affects biodiversity to prevent its negative impact.

Here, we discuss the major impacts of human activity specifically on plant biodiversity and examine how this may be tackled.

How human activity impacts plant biodiversity

For decades we have understood that human activity is responsible for environmental changes. In general, these changes have been detrimental to the environment.

Scientists predict that within the next 50 to 100 years human activity will have created regional combinations of environmental conditions that may be inhabitable by many of the terrestrial plants that evolved to survive in particular regions.

This will likely force a significant amount of plant species to extinction. Therefore, human activity threatens to significantly reduce plant biodiversity.

Human activity manipulates many factors that are vital to maintaining the complex ecosystems in which thousands of plant species are adapted to. Factors such as the natural levels of numerous elements including nitrogen, calcium, phosphorus, and atmospheric CO2, as well as levels of herbivores, pathogens, and predators. Human activity also modifies the climate, which has a huge impact on life on the planet.

Ecosystems are fragile. Particular species thrive in certain ecosystems because they have physiologies, morphologies, and life histories that allow them to thrive within a specific set of environmental constraints.

Once these constraints are amended, the species is no longer optimally adapted for life there, and because human activity causes these constraints to modify rapidly, rather than throughout hundreds of years, natural selection cannot play a part in seeing the plants adapt to these new settings.

Once human activity changes even one constraint, many species that were once superior competitors can easily be displaced by just a few species that now have advantageous characteristics to best suit the environment. This can drastically change the ecosystem, and end in the extinction of plant species.

Below we outline the major ways in which human activity impacts plant biodiversity.

Population growth

The human population continues to grow exponentially. This is causing us to need more land to live on, to build more houses, hospitals, schools, supermarkets and more. It also means more crops are required and more waste is produced. As a result, the land is often cleared to make space for this.

Image Credit: Arthimedes/Shutterstock.com

Habits are built on or turned into farmland. The removal of these natural habits directly reduces the number of plants and can lead to some species becoming endangered due to a lack of an appropriate habitat to support them.

Deforestation

Deforestation reduces plant biodiversity both directly and indirectly. Directly it reduces plant biodiversity throughout the destruction of natural habitats. Indirectly it decreases biodiversity due to the techniques used in deforestation that emit carbon dioxide into the atmosphere, adding to global warming.

Slash and burn is a popular technique around the world for clearing forest areas, it involves burning the tree debris, releasing carbon dioxide as the plant waste burns.

It is estimated that as many as several hundred species of animals, plants, and insects are lost every day due to deforestation and other factors. Deforestation is causing plant species to become extinct and reducing biodiversity.

Fertilizer use

The overuse of fertilizers can reduce plant biodiversity by causing eutrophication. Fertilizers contain high levels of nitrates. When they are added to the soil, a proportion of the fertilizers runoff into rivers and lakes, introducing nitrates into these aquatic ecosystems.

Increased nitrate levels cause an overgrowth of the algae that live on the water's surface, blocking out the light entering the water, and causing plants beneath the surface that rely on photosynthesis to die. Because of fertilizer use, the biodiversity of rivers and lakes is reducing.

Tourism

Tourism has numerous direct effects on biodiversity. Activities such as horse riding, mountain biking, and ATV driving not only trample the land and the plant life on it but also often require the clearing of habitats to provide space for this to take place.

Also, trails added into areas of high biodiversity can encourage certain species of weed to grow into the trails and out onto the roads, reducing the prevalence of other species.

Pathogens can also be introduced into ecosystems through tourism, and numbers of rare plants are sometimes reduced by human collection. It is estimated that around 72 plant taxa in Australia are currently under threat due to tourism.

Tackling the loss of plant biodiversity

While human activity is having a significant impact on plant biodiversity, fortunately, there are strategies in place to reduce this. Deforestation is being reduced and numerous initiatives are in place around the world to tackle greenhouse gases.

Reforestation is also underway, with trees being replanted to replace those cut-down. Recycling rates are on the rise, reducing the volume of waste entering landfill sites. Finally, more national parks are being set up to protect and develop endangered habitats.

Sources:

Kelly, C., Pickering, C. and Buckley, R., 2003. Impacts of tourism on threatened plant taxa and communities in Australia. Ecological Management & Restoration, 4(1), pp.37-44. onlinelibrary.wiley.com/doi/abs/10.1046/j.1442-8903.2003.00136.x

Tilman, D. and Lehman, C., 2001. Human-caused environmental change: Impacts on plant diversity and evolution. Proceedings of the National Academy of Sciences, 98(10), pp.5433-5440. https://www.pnas.org/content/98/10/5433

Pickering, C. and Hill, W., 2007. Impacts of recreation and tourism on plant biodiversity and vegetation in protected areas in Australia. Journal of Environmental Management, 85(4), pp.791-800. https://www.sciencedirect.com/science/article/pii/S030147970600377X

Further Reading

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Effect of Human Activity on Plant Biodiversity

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Biodiversity refers to the variety and variability of all life on earth. Due to the process of evolution, thousands of species of animals and plants now exist on the planet. Biodiversity encompasses the wide range of genes, species, and ecosystems that have become established on the planet, which intertwines and impact each other.

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EON

ERA

PERIOD

EPOCH

BEGINNING

MAJOR EVENTS

GLOBAL
EXTINCTION
EVENT

P
H
A
N
E
R
O
Z
O
I
C
Quaternary Holocene
11, 700
present climate; only modern humans

Pleistocene
2,600,000

recent ice ages; various human species

Tertiary Pliocene
5,300,000

near-human species and other near-modern mammals

Miocene
23,000,000
apes flourish; savanna grazing animals evolve

Oligocene
33,900,000

monkeys, apes, and other mammal families evolve

Eocene
55,800,000
prosimians flourish; possible early monkeys

Paleocene
65,500,000
earliest primates (proto-prosimians)

Mesozoic(age of reptiles)
Cretaceous
145,500,000

archaic mammals and birds begin to replace dinosaurs; first flowering plants

65,500,000
(76% of species lost)

Jurassic
199,600,000

dinosaurs dominant; primitive mammals spread; toothed birds

Triassic
251,000,000

first dinosaurs and first egg-laying mammals; vast forests of ferns, conifers, and cycads

200,000,000
(80% of species lost)

Permian

299,000,000

spread of reptiles and insects; first mammal-like reptiles

251,000,000
(95-96% of species lost: earth's largest mass extinction)

Carboniferous
359,200,000
amphibians dominant; forests flourish; reptiles and modern insects appear

Devonian
416,000,000
fish dominant; amphibians appear; first forests

360,000,000
(83% of species lost)

Silurian
443,700,000
fish with jaws; first air breathing animals

Ordovician
488,300,000
invertebrates dominant; first vertebrates (jawless fish); first land plants
444,000,000
(85% of species lost)

Cambrian 542,000,000 explosion of life forms; invertebrates dominant (worms, jellyfish, trilobites, etc.)
488,000,000?

P
R
E
C
A
M
B
R
I
U
M

3,000,000,000 protozoa, sponges, and algae; oxygen begins to accumulate in the atmosphere

3,500,000,000
first clear evidence of life (one celled bacteria)

4,540,000,000

origin of the earth

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Early Primate Evolution: Time Scale of the Earth

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251,000,000 (95-96% of species lost: earth’s largest mass extinction)

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Abstract

The conservation of plants has not generated the sense of urgency-or the funding-that drives the conservation of animals, although plants are far more important for us. There are an estimated 500,000 species of land plants (angiosperms, gymnosperms, ferns, lycophytes, and bryophytes), with diversity strongly concentrated in the humid tropics. Many species are still unknown to science. Perhaps a third of all land plants are at risk of extinction, including many that are undescribed, or are described but otherwise data deficient. There have been few known global extinctions so far, but many additional species have not been recorded recently and may be extinct. Although only a minority of plant species have a specific human use, many more play important roles in natural ecosystems and the services they provide, and rare species are more likely to have unusual traits that could be useful in the future. The major threats to plant diversity include habitat loss, fragmentation, and degradation, overexploitation, invasive species, pollution, and anthropogenic climate change. Conservation of plant diversity is a massive task if viewed globally, but the combination of a well-designed and well-managed protected area system and ex situ gap-filling and back-up should work anywhere. The most urgent needs are for the completion of the global botanical inventory and an assessment of the conservation status of the 94% of plant species not yet evaluated, so that both in and ex situ conservation can be targeted efficiently. Globally, the biggest conservation gap is in the hyperdiverse lowland tropics and this is where attention needs to be focused.

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Plant diversity in a changing world: Status, trends, and conservation needs

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The conservation of plants has not generated the sense of urgency-or the funding-that drives the conservation of animals, although plants are far more important for us. There are an estimated 500,000 species of land plants (angiosperms, gymnosperms, ferns, lycophytes, and bryophytes), with diversity strongly concentrated in the humid tropics.

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Earth looked very different long ago. Search for addresses across 750 million years of Earth's history.

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Earth is a planet defined by change, swinging through periods of intense heat and deep freeze even as oceans and continents are reshaped by the actions of plate tectonics. This constant reconfiguration has been a huge driver in the development of life on Earth. But scientists agree that human activity has now begun to influence the planet, changing the climate and drastically altering surface conditions.

Understanding how humans are affecting Earth's system requires a better grasp on the natural cycles and events that have shaped our planet through deep time. Slide through the timeline above to explore how the globe has changed over seven major "snapshots" in our climate history, and to see how it might look in the far future.
is Vice President of International Mapping in Ellicott City, Maryland. Tim Montenyohl is professor emeritus of geology at Northern Arizona University and founder of Colorado Plateau Geosystems Inc. is a 3-D Artist and Animator at International Mapping.
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Travel Through Deep Time With This Interactive Earth

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Earth is a planet defined by change, swinging through periods of intense heat and deep freeze even as oceans and continents are reshaped by the actions of plate tectonics. This constant reconfiguration has been a huge driver in the development of life on Earth.

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The Evolution Of Angiosperms (Flowering Plants)

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Why is biodiversity so important? - Kim Preshoff