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The formation of the planet earth kicks off here!
The surface is covered in magma from belching volcanoes.
No life form. The moon is created.

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The Hadean is the geological eon before the Archaean. It began at the Earth's formation about 4.6 billion years ago, and ended 4 billion years ago. The name "Hadean" comes from Hades, Greek for "Underworld", due to the conditions on the Earth at the time. The geologist Preston Cloud first used the term in 1972. Meteorite bombardment, volcanism and high temperatures were very widespread on the early Earth.

There are no sedimentary rocks from the Hadean at all. The earliest geological objects on Earth are some zircons, dated to about 4,400 million years ago (mya). Oceans would probably have formed as soon as the temperature allowed. It is thought that constant bombardment kept the Earth in a molten state until about the end of the eon.

Early in Earth history, the Moon was torn out by a massive collision with a proto-planet. The evidence for this giant impact hypothesis is:

1. the remarkable similarity between the Earth's crust and the Moon's composition,

2. the low iron concentration in the Moon's centre, and

3. the high angular momentum of the Earth-Moon system.

An explanation for the general lack of Hadean rocks (older than 3800 mya) is the large amount of rocky and icy debris present in the early Solar System. After the eight planets formed, large numbers of leftover proto planets, asteroids, and comets pursued eccentric orbits throughout our system, bombarding the early Earth and the other planets and moons until approximately 3800 mya. This activity may have prevented any large crustal fragments from forming by literally shattering the early protocontinents. A barrage of particularly large impacts known as the Late Heavy Bombardment represents the climax of this violent era.

No life forms are known from this eon. The early atmosphere contained carbon dioxide, methane and nitrogen, but almost no oxygen.

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The Hadean is the geological eon before the Archaean. It began at the Earth's formation about 4.6 billion years ago, and ended 4 billion years ago. The name "Hadean" comes from Hades, Greek for "Underworld", due to the conditions on the Earth at the time. The geologist Preston Cloud first used the term in 1972.

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Simple forms of life kicks off here!

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The Archaean (or Archean) eon is the geological period after the Hadean and before the Proterozoic. It is one of the four main time periods ( eons) of Earth history. The Archaean lasted from 4,000 million years ago (mya) to 2,500 mya. It contains the first sedimentary rocks, and the first fossil life forms, which were cyanobacteria, and acritarchs.

Most of the rocks which survive are volcanic ( igneous) and metamorphic in origin. Volcanic activity was everywhere. When the Archaean began, the Earth's heat flow was nearly three times higher than it is today. It was still twice the current level when the Archaean ended, 2,500 mya. This high level of heat flow may have made plate tectonics more vigorous than today. The question of when plate tectonics began is a major research area. The large supercontinent Vaalbara formed in the Archaean. There were oceans already, before the Archaean. The atmosphere almost entirely lacked free oxygen, and instead, it was mostly methane and .

Fossil bacterial mats, called stromatolites, are found throughout the Archaean after about 3,500mya. These were formed by cyanobacteria, which used photosynthesis and gave off oxygen as a by-product. Initially, this oxygen was absorbed by combining with iron ions in solution. Not until much later did oxygen build up in the atmosphere.

Fossil raindrop marks have been found in the later Archaean, 2,700 mya. The rocks were discovered in Ventersdorp in the North West Province of South Africa in the 1980s.

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The Archaean (or Archean) eon is the geological period after the Hadean and before the Proterozoic. It is one of the four main time periods ( eons) of Earth history. The Archaean lasted from 4,000 million years ago (mya) to 2,500 mya.

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The Proterozoic eon comes before the Phanerozoic. It was a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life". The Proterozoic Eon extended from 2500 million years ago (mya) to 541 mya. It is the most recent part of the former Precambrian.

The Proterozoic consists of 3 geologic eras, from oldest to youngest:

The well-identified events were:

Study of these rocks shows that the eon featured massive, rapid continental accretion (unique to the Proterozoic), supercontinent cycles, and mountain building.

Related pages

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The Proterozoic eon comes before the Phanerozoic. It was a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life". The Proterozoic Eon extended from 2500 million years ago (mya) to 541 mya. It is the most recent part of the former Precambrian.

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Phanerozoic Eon - Paleozoic Era  541mya -252mya

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Phanerozoic Eon - Paleozoic Era  541mya -252mya

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Periods
*Cambrian
*Ordovician
*Silurian
*Devonian
*Carboniferous
*Permian

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The Cambrian is the first geological period of the Palaeozoic era and the Phanerozoic eon. It lasted from 541 million years ago to 485.4 million years ago. Before it came the Ediacaran, and after it the Ordovician.

Biologists have learnt quite a lot about the soft parts of Cambrian animals. This is because places have been found where soft parts of organisms are preserved as well as their more resistant shells. This means our understanding of the Cambrian biota is better than that of some later periods.

Life on Earth changed greatly during the Cambrian period. Before the Cambrian, life was mostly small and simple. Complex organisms ( metazoa) evolved during the Proterozoic era. But during the Cambrian period, some organisms used carbonate minerals for shells, so they had hard parts which could become fossils. There were many different kinds of life during the Cambrian period. This increase in the diversity of lifeforms was relatively rapid, and is called the Cambrian explosion. This adaptive radiation produced the first members of the main groups of animals, called phyla.

Almost all of this new life was in the oceans. There was little life on land except a layer of microbes. There were shallow seas near several continents, because a supercontinent called Pannotia had broken into smaller pieces. The seas were warm, and there was no ice at the North and South Pole. Many animals with hard shells appeared for the first time during the beginning of the Cambrian.

Change in the sea floor

At the start of the Cambrian, the earlier animals (the Ediacaran biota) may have become extinct. It seems these older life forms were affected by new types which burrowed into the sea floor. This changed the conditions of life for the older types. The burrowing must have disturbed the mat of bacteria and algae which covered the sea-floor. About this time we find the first examples of many phyla. There are also some fossil traces on what was land at the time, so perhaps a few Cambrian organisms did leave the water.

Fossils from the Cambrian period sometimes show what the soft parts were like, unlike most fossils where the soft parts disappear. Fossils from the Burgess Shale in Ontario, Canada are examples of fossils with soft parts. Here are some life forms that first appeared in the Cambrian period, with the oldest ones first:

It is not always clear which phylum a fossil should be put into. So there are some fossils which are still being discussed, years after they were discovered.

Images for kids

A reconstruction of Margaretia dorus from the Burgess Shale, which were once believed to be green algae, but are now understood to represent hemichordates.

Stromatolites of the Pika Formation (Middle Cambrian) near Helen Lake, Banff National Park, Canada

Opabinia was a creature with an unusual body plan; it was probably related to arthropods

Protichnites were the trackways of arthropods that walked Cambrian beaches

Hallucigenia may have been an early ancestor of the Velvet worms. Reconstructions of H. sparsa, H. hongmeia, and H. fortis

Size comparison of different Cambrian species

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The Cambrian is the first geological period of the Palaeozoic era and the Phanerozoic eon. It lasted from 541 million years ago to 485.4 million years ago. Before it came the Ediacaran, and after it the Ordovician. Biologists have learnt quite a lot about the soft parts of Cambrian animals.

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The Ordovician is the second period of the Paleozoic era. It lasted from about 485.4 million years (mya) to 443.4 mya. It follows the Cambrian period and is followed by the Silurian period.

The Ordovician was named after the Welsh tribe of the Ordovices. It was defined by Charles Lapworth in 1879. He recognized that the fossils in the disputed strata were different from those of the Cambrian or the Silurian. Therefore, he reasoned, they should be placed in a period of their own.

Recognition of the Ordovician period was slow in Britain, but elsewhere it was quickly accepted. In 1906 it was adopted as an official period of the Paleozoic era by the International Geological Congress.

The Ordovician ended with a series of extinction events that, together amount to the second greatest extinction of the Phanerozoic. This was the End-Ordovician extinction event.

Palaeogeography

Sea levels were high during the Ordovician. Shallow (<50 metres) inland seas were the greatest for which evidence is preserved in the rocks.

During the Ordovician, the southern continents collected into a single continent called Gondwana. Gondwana started the period in equatorial latitudes and, as the period progressed, drifted toward the South Pole. Early in the Ordovician, the continents Laurentia (present-day North America), Siberia, and Baltica (present-day northern Europe) were still independent continents.

Geochemistry

The Ordovician was a time of calcite sea geochemistry in which low- magnesium calcite was the main marine precipitate of calcium carbonate.

For most of the Ordovician, life continued to flourish, but near the end of the period the End-Ordovician extinction event seriously affected planktonic forms like conodonts, graptolites, and some groups of trilobites. Brachiopods, bryozoans and echinoderms were also heavily affected, and the cone-shaped nautiloids died out completely, except for rare Silurian forms.

The extinctions may have been caused by an ice age that occurred at the end of the Ordovician period: the end of the Ordovician was one of the coldest times in the last 600 million years of earth history.

On the whole, the fauna that emerged in the Ordovician set the scene for the rest of the Palaeozoic. The fauna was dominated by suspension feeders, mainly with short food chains. The ecological system reached a new level of complexity far beyond that of the Cambrian fauna.

Though less famous than the Cambrian explosion, the Ordovician featured an adaptive radiation, which was no less remarkable. Marine genera increased fourfold, resulting in 12% of all known Phanerozoic marine fauna. Another change in the fauna was the strong increase in filter feeding organisms. The articulate brachiopods, cephalopods, and crinoids took over. Articulate brachiopods, in particular, largely replaced trilobites in shelf communities. This illustrates the greatly increased biodiversity of carbonate shell-secreting organisms in the Ordovician compared to the Cambrian. Although solitary corals date back to at least the Cambrian, reef-forming corals appeared in the early Ordovician.

Molluscs, which appeared during the Cambrian or even the Ediacaran, became common and varied, especially bivalves, gastropods, and nautiloid cephalopods. Now-extinct marine animals called graptolites thrived in the oceans. Some new cystoids and crinoids appeared.

It was long thought that the first true vertebrates (fish - Ostracoderms) appeared in the Ordovician, but recent discoveries in China show they probably originated in the Lower Cambrian. The very first Gnathostomata (jawed fish) appeared in the Upper Ordovician.

During the Middle Ordovician there was a large increase in bioeroding (shell and rock-boring) organisms. This is known as the Ordovician Bioerosion Revolution. It is marked by a sudden abundance of hard substrate trace fossils.

In the Lower Ordovician, trilobites were joined by many new brachiopods, bryozoans, planktonic graptolites and conodonts, and many types of molluscs and echinoderms, including the ophiuroids ("brittle stars") and the first sea stars. Nevertheless the trilobites remained abundant, with all the Late Cambrian orders continuing, and being joined by the new group Phacopida. The first evidence of land plants also appeared.

Trilobites in the Ordovician were very different from their predecessors in the Cambrian. Many trilobites developed bizarre spines and nodules to defend against predators such as primitive sharks and nautiloids. Other trilobites evolved to become swimming forms. Some trilobites even developed shovel-like snouts for ploughing through muddy sea bottoms. Some trilobites such as Asaphus kowalewski evolved long eyestalks to assist in detecting predators whereas other trilobite eyes in contrast disappeared completely.

Trypanites borings in an Ordovician hardground, southeastern Indiana.

Petroxestes borings in an Ordovician hardground, southern Ohio.

Recent discovery of Burgess Shale types

The renowned Burgess Shale fauna disappears in the Middle Cambrian. It is now known that it did not go extinct, but survived, and thrived where the circumstances were right. A recently discovered lagerstätte (a deposit of exceptionally preserved fossils) has been found in the Fezouata Formation, Morocco. The site contains remarkable fossils of soft-bodied animals from a muddy ocean floor. The fauna also includes some hard-bodied animals such as horseshoe crabs. Probably low oxygen conditions kept predators and scavengers to a minimum.

Images for kids

External mold of Ordovician bivalve showing that the original aragonite shell dissolved on the sea floor, leaving a cemented mold for biological encrustation (Waynesville Formation of Franklin County, Indiana).

Upper Ordovician edrioasteroid Cystaster stellatus on a cobble from the Kope Formation in northern Kentucky with the cyclostome bryozoan Corynotrypa in the background

Bryozoan fossils in Ordovician kukersite oil shale, northern Estonia

The heliolitid coral Protaraea richmondensis encrusting a gastropod; Cincinnatian (Upper Ordovician) of southeastern Indiana

In Spanish: Ordovícico para niños

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Mean atmospheric content over period duration

c. 14 vol %
(70 % of modern level)

Mean atmospheric content over period duration

c. 4500 ppm
(16 times pre-industrial level)

Mean surface temperature over period duration

c. 17 °C
(3 °C above modern level)

Sea level (above present day)

Around 180m, with short-term negative excursions

The Silurian was the period from the end of the Ordovician, about 443.4 million years ago (mya) to the beginning of the Devonian period, about 419 mya.

As with other geologic periods, the rock beds that define the period's start and end are well identified, but the exact dates are uncertain by several million years. The base of the Silurian is set at a major extinction when 60% of marine species were wiped out, the Ordovician-Silurian extinction events.

First terrestrial biota

The Silurian was the first period to see macrofossils of biota on land, in the form of moss forests along lakes and streams as well as millipedes and scorpions colonizing the land later in the period. The fossil record of Sea Scorpions reached it's greatest extent in the middle silurian,about 430 million years ago.

The first fossil records of vascular plants, that is, land plants with tissues that carry food, appeared in the second half of the Silurian period. The earliest known representatives of this group are the Cooksonia (mostly from the northern hemisphere) and Baragwanathia (from Australia). A primitive Silurian land plant with xylem and phloem but no differentiation in root, stem or leaf, was much-branched Psilophyton. This plant reproducied by spores and respired through stomata on every surface, and probably photosynthesizing in every tissue exposed to light.

Some evidence suggests the presence of primitive predatory arachnids and myriapods in Late Silurian rocks. Predatory invertebrates would indicate that simple food webs were in place that included non-predatory prey animals.

Images for kids

Silurian sea bed fossils collected from Wren's Nest Nature Reserve, Dudley UK

Silurian sea bed fossils collected from Wren's Nest Nature Reserve, Dudley UK

Artist's impression of Silurian underwater fauna

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Mean atmospheric content over period duration c. 14 vol % (70 % of modern level) Mean atmospheric content over period duration c. 4500 ppm (16 times pre-industrial level) Mean surface temperature over period duration c.

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The Devonian is the fourth period of the Paleozoic era and the Phanerozoic eon. It lasted from about 419 million years ago (mya) to about 359 mya. It is named after Devonshire, England, where rocks from this period were first studied.

Sea levels were high, and there was a great variety of fish and other marine organisms. The Devonian fish included the Agnatha (jawless fish), the Acanthodii (spiny fish), the Placoderms (armoured fish), the Chondrichthyes (cartilaginous fish), and the early Osteichthyes (bony fish). The Devonian strata are divided into lower, middle and upper subdivisions.

During the Devonian the evolution of fish into tetrapods occurred. Various terrestrial arthropods also became established. The first seed-bearing plants spread across dry land, forming huge forests.

The supercontinent of Gondwana was to the south, and the continent of Siberia to the north. The early form of the small continent of Euramerica was in between. The supercontinent Pangaea was just starting to form.

By the late Devonian, the land had been colonized by plants and insects. In the oceans, massive reefs were built. Euramerica and Gondwana were beginning to converge into what would become Pangaea.

Period ended with extinctions

Tectonic and volcanic activity was high. A series of extinction events occurred towards the end of the Devonian, including a major event at the Frasnian-Famennian boundary in the Late Devonian, about 364 mya.

A major extinction occurred at the start of the last phase of the Devonian period, the Frasnian-Famennian boundary, about 372.2 mya. Almost all the fossil agnathan fishes suddenly disappeared. A second strong extinction closed the Devonian period. The late Devonian extinction was one of five major extinction events in the history of the Earth. The cause or causes are not known.

Images for kids

The rocks of Lummaton Quarry in Torquay in Devon played an early role in defining the Devonian period.

The Devonian period marks the beginning of extensive land colonisation by plants. With large land-dwelling herbivores not yet present, large forests grew and shaped the landscape.

Dunkleosteus, one of the largest armoured fish ever to roam the planet, lived during the Late Devonian

Early shark Cladoselache, several lobe-finned fishes, including Eusthenopteron that was an early marine tetrapod, and the placoderm Bothriolepis in a painting from 1905

Melocrinites nodosus spinosus, a spiny, stalked crinoid from the Middle Devonian of Wisconsin

Enrolled phacopid trilobite from the Devonian of Ohio

The common tabulate coral Aulopora from the Middle Devonian of Ohio - view of colony encrusting a brachiopod valve

Devonian spiriferid brachiopod from Ohio which served as a host substrate for a colony of hederelloids

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The Devonian is the fourth period of the Paleozoic era and the Phanerozoic eon. It lasted from about 419 million years ago (mya) to about 359 mya. It is named after Devonshire, England, where rocks from this period were first studied.

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The Carboniferous was the geological period after the Devonian and before the Permian. It lasted from about 359 to about 299 million years ago. It is the fifth period of the Paleozoic era and the Phanerozoic eon.

In the U.S.A. the Carboniferous is divided into the Mississippian (lower part, 359-323.2 mya) and the Pennsylvanian (upper part, 323.2-299 mya). In Europe the terms lower, middle and upper are used.

Vertebrate evolution

The early tetrapods split first into two major groups: the amphibians, which laid their eggs in water, and the amniotes, who laid their cleidoic eggs on land. The amniotes gave rise to two groups both of which became dominant at different times. They were the synapsids, which eventually gave rise to the mammals, and the sauropsids, which gave rise to the dinosaurs and other reptiles. These momentous events took place in the lower part of the Carboniferous, the Mississippian.

The Carboniferous is named after the coal measures, the remains of peat formed by dense tropical wetland forests. New kinds of vascular plants with thick bark grew in the forests. Much of the coal came from this bark. This biota occurred in the upper part of the period, the Pennsylvanian, from 315-300 million years years ago.

These forests were on the equator, and the wetlands, which are always low-lying, stretched across the supercontinent of Laurussia. This included what is now North America in the west, through what is now Europe to China in the east. The river plain which was the heart of the wetland stretched 5000 km from eastern Canada to the Ukraine, and was 700 km wide. p6

This kind of climate and geography has no exact parallel today, but the peat swamp forests in Indonesia and Malaysia, the Amazon Basin, the Mississippi River system and the Okefenokee swamp give some idea. The swamps were dominated by giant clubmosses, including Lepidodendron. They were the earliest trees, later replaced by conifers and flowering plants. Sometimes other plants from the levee got swept down by the river, such as horsetails, ferns and tree-like pteridosperms.

The wetland forests ended when the land level was raised by the pressure of the Gondwana continent against Laurussia. This caused the zone of contact to rise. The end of the coal measures marks the end of the Carboniferous period. China was too far away to be affected. There, the wetland forests continued for another 50 million years, into the Permian. p30

Images for kids

Generalized geographic map of the United States in Middle Pennsylvanian time.

Ancient in situ lycopsid, probably Sigillaria, with attached stigmarian roots.

Aviculopecten subcardiformis; a bivalve from the Logan Formation (Lower Carboniferous) of Wooster, Ohio (external mold).

Bivalves ( Aviculopecten) and brachiopods ( Syringothyris) in the Logan Formation (Lower Carboniferous) in Wooster, Ohio.

Syringothyris sp.; a spiriferid brachiopod from the Logan Formation (Lower Carboniferous) of Wooster, Ohio (internal mold).

Palaeophycus ichnosp.; a trace fossil from the Logan Formation (Lower Carboniferous) of Wooster, Ohio.

Akmonistion of the shark order Symmoriida roamed the oceans of the early Carboniferous.

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The Carboniferous was the geological period after the Devonian and before the Permian. It lasted from about 359 to about 299 million years ago. It is the fifth period of the Paleozoic era and the Phanerozoic eon. In the U.S.A. the Carboniferous is divided into the Mississippian (lower part, 359-323.2 mya) and the Pennsylvanian (upper part, 323.2-299 mya).

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Triassic period
Jurassic period
Cretaceous period

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The Triassic is the first geological period in the Mesozoic era and the seventh period of the Phanerozoic eon. It lasted 50.6 million years. The period began 251.9 million years ago, and ended 201.3 million years ago.

The period before the Triassic was the Permian period, the last period in the Palaeozoic era. The Jurassic period came after the Triassic.

Many new groups arose during the Triassic period, including the dinosaurs and the first mammals.

Extinction events

Great extinction events happened at both the beginning and end of the Triassic period. The Triassic began after the great extinction at the end of the Palaeozoic era, the Permian/Triassic extinction event. Nobody really knows the exact cause of the Permian/Triassic extinction, but many experts have different theories. Generally, experts agree that many things caused the extinction.

The Triassic had several more extinction events, whose causes are also unknown. The most significant of these took place at the end of the Triassic, which was one of the 'big five' Phanerozoic marine extinctions.

The name 'Triassic' comes from the three rock strata that formed during the Triassic period ("tri" means "three"). Three layers of rock strata formed during this period:

Overall climate

On average, the Triassic's climate was very different from today's:

1. It had about 80% of today's oxygen levels

2. There was about six times as much carbon dioxide in the air as there was before the Industrial Revolution

3. The Earth's average surface temperature was about 3o C hotter than it is now

Paleogeography

During the Triassic period, there were no separate continents like there are today. Almost all the Earth's land mass was together in a single supercontinent called Pangaea ("all the land"). Pangaea was centered more or less on the equator. All the deep-ocean sediments (the things that settled at the bottom of the ocean) had disappeared. This happened because oceanic plates moved sideways and downward until they were finally on top of each other, or under each other.

The supercontinent Pangaea was rifting during the Triassic - especially late in the period - but had not yet separated into different continents.

Being a super-continental land mass, Pangaea had limited shoreline. Because of this, Triassic marine deposits - fossils from Triassic ocean life - are rare in most of the world. In North America, for example, marine deposits are limited to a few exposures in the west. However, they are common in Western Europe, where the Triassic was first studied.

Major adaptive radiations

The first part of the Triassic had much less variety than the Permian, and showed signs of a deteriorated environment. This situation lasted for about 5 million years, then steadily improved. Into the vacant ecological niches, new forms evolved, replacing old with new. This rapid adaptive radiation happened to the reptiles on land, the fish in the seas, and a number of other groups, like the insects. Diverse communities with complex ecology took 30 million years to re-establish.

The group of bony fish known as the teleosts first appeared during the Triassic period. The group now includes over 80% of all fish and 95% of all bony fish. The only other common group of fish are the Chondrichthyes (the sharks and rays). The rays also appeared during the Triassic.

Many reptile groups first appeared during the Triassic period, possibly because so many niches were vacant at the time. Some of these new groups died out in the End-Triassic extinction event, but those that survived ruled the Earth for the rest of the Mesozoic. Examples include:

This was a major change, because in the middle Triassic period, the Synapsids ( mammals' ancestors) were still dominant.

The end-Triassic extinction

Many reptile groups became extinct during the Triassic, including: p. 41

Also, amongst the Synapsids (which used to be called mammal-like reptiles), the Dicynodonts died out during the end-Triassic extinction. p. 41

The Triassic was a period of great change in tetrapods: many new and important groups appeared, but many others became extinct. Of all the periods in the Mesozoic era, there are the least number of fossils from the Triassic period. This makes it difficult for scientists to explain these events.

Related pages

Images for kids

Triassic flora as depicted in Meyers Konversations-Lexikon (1885-90)

Immediately above the Permian-Triassic boundary the glossopteris flora was suddenly largely displaced by an Australia-wide coniferous flora.

Triassic sandstone near Stadtroda, Germany

Skull of a Triassic Period Phytosaur found in the Petrified Forest National Park

Postosuchus An apex predator of its time which preyed on anything smaller than itself

Lystrosaurus was the most common land vertebrate during the Early Triassic, when animal life had been greatly diminished

Reconstruction of Proterosuchus, a genus of crocodile-like carnivorous reptile that existed in the Early Triassic

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The Triassic is the first geological period in the Mesozoic era and the seventh period of the Phanerozoic eon. It lasted 50.6 million years. The period began 251.9 million years ago, and ended 201.3 million years ago. The period before the Triassic was the Permian period, the last period in the Palaeozoic era.

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The Jurassic is the second and middle geological period in the Mesozoic era and the eighth period in the Phanerozoic eon. It began 201.3 million years ago, and ended 145 million years ago. The Jurassic period happened between the Triassic and Cretaceous periods.

During the Jurassic period, the climate was hotter and wetter than it is today. Carbon dioxide levels and sea levels were also higher than today.

The Kimmeridge Clay of the Upper Jurassic was laid down in an environment which does not exist on the earth today. Much of Western Europe was covered by a high sea level. The supercontinent Pangaea was beginning to break up, causing a narrow Atlantic Ocean. Because of this, the United Kingdom was covered by a shallow and largely anoxic sea, perhaps less than 100 metres deep, with occasional landmasses.

This was shallower water than the Blue Lias of the Lower Jurassic. It was often low in oxygen, which caused its organic material to decompose, but only partially. The Jurassic's mudstones are organic-rich, and gave rise to most of the North Sea oil.

Plate tectonics

During the early or Lower Jurassic, the supercontinent Pangaea broke up into the northern supercontinent Laurasia and the southern supercontinent Gondwana. This was the start of the break-up of Pangaea, a process which took a long time to complete. The process of pulling apart in geology is called rifting.

Floods of lava flowed from fissures (splits) and volcanos. By the end of the Jurassic, South America had begun to part from Africa. In the western part of North America, mountain ranges began to form. This continued as the American tectonic plates gradually moved west. The westward-moving North American plates gradually rode over the Pacific Ocean plates to form the Rocky Mountains.

Paleontology

On sea and land, evolutionary trends which started in the Upper Triassic continued through the Jurassic. Archosaurian reptiles dominated the land biota. Reptile groups radiated and filled many niches. Dinosaurs, pterosaurs, marine reptiles ( Ichthyosaurs, Plesiosaurs, turtles) all flourished.

Amongst Invertebrates, there was much change. Modern predators like starfish, crabs, and hole-boring gastropods took over the sea floor, eating the benthic fauna in huge numbers. Brachiopods lost their grip on the in- shore habitats; molluscan bivalves took their place.

Early mammals existed, but mostly as small creatures living in burrows, on the margins of a reptilian world. The first fossils of small dinosaurs with feathers, called Anchiornis, come from the Jurassic period. The first fossil bird, Archaeopteryx, comes from the Upper Jurassic.

Land plants

The dominant land plants were the gymnosperms ( conifers). Ferns, large horsetails,' monkey puzzle' trees, ginkgos and cycads were common. These trees were not easy to digest, compared to modern flowering plant trees (Angiosperms). They must have spent longer in the gut than the food of modern herbivores. That would make increased size an advantage for sauropods, which did indeed become much larger in the Jurassic than any any land life had before.

Related pages

Images for kids

Terrestrial environment of the Toarcian of Łęczna (Ciechocinek Formation, Lublin, Poland), based on the Bogdanka Coal Mine Flora. Dinosaurs are based on material found on various locations of the formation

Jurassic limestones and marls (the Matmor Formation) in southern Israel

Gigandipus, a dinosaur footprint in the Lower Jurassic Moenave Formation at the St. George Dinosaur Discovery Site at Johnson Farm, southwestern Utah

The Permian through Jurassic stratigraphy of the Colorado Plateau area of southeastern Utah

Aurornis xui, which lived in the late Jurassic, may be the most primitive avialan dinosaur known to date, and is one of the earliest avialans found to date.

Skeleton of Monolophosaurus, a basal tetanuran from the Middle Jurassic of China

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The Jurassic is the second and middle geological period in the Mesozoic era and the eighth period in the Phanerozoic eon. It began 201.3 million years ago, and ended 145 million years ago. The Jurassic period happened between the Triassic and Cretaceous periods. During the Jurassic period, the climate was hotter and wetter than it is today.

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Paleogene Period
Neogene Period
Quaternary Period

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65mya - 23mya

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The Palaeogene (meaning "old generation" in Greek) is the first geological period of the Cainozoic and the tenth period in the Phanerozoic eon. It began 65 million years ago, and ended 23 million years ago. Before it was the Cretaceous. The Palaeogene was followed by the Neogene.

The Palaeogene had three stages: Palaeocene, Eocene and Oligocene.

The Palaeogene, along with the succeeding Neogene were originally together considered one period, the Tertiary until recently, when it was split.

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The Palaeogene (meaning "old generation" in Greek) is the first geological period of the Cainozoic and the tenth period in the Phanerozoic eon. It began 65 million years ago, and ended 23 million years ago. Before it was the Cretaceous. The Palaeogene was followed by the Neogene.

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The Miocene is the first epoch of the Neogene period of the Cainozoic. It started about 23 million years ago and ended about 5.33 million years ago. The rock beds that mark the start and end are well known, but the exact dates of the start and end of the period are uncertain. The biota becomes 'modern'.

The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words μείων (, "less") and καινός (, "new") and means "less recent", because it has 18% fewer modern sea invertebrates than the Pliocene.

As the earth cooled, it went from the Oligocene epoch, through the Miocene, and into the Pliocene. The Miocene boundaries are not set at any particular world wide event. They are set at regional boundaries between the warmer Oligocene and the cooler Pliocene epochs.

The plants and animals of the Miocene were fairly modern. Modern families of mammals and birds existed. Whales, seals, and kelp spread. Modern sharks appeared, including the huge . Grasslands became more common. Mammalian browsers became less common, and grazer species became more common. About 100 species of ape lived at that time, and cetaceans were very common in the seas. The giganic shark Carcharodon megalodon may have preyed on them.

Life during the Miocene Epoch was mostly supported by the two newly formed biomes, kelp forests and grasslands. Grasslands allow for more grazers, such as horses, rhinoceroses, and hippos. Ninety five percent of modern plants existed by the end of this epoch.

The coevolution of gritty, fibrous, fire-tolerant grasses and long-legged gregarious ungulates with high-crowned teeth, led to a major expansion of grass-grazer ecosystems, with roaming herds of large, swift grazers pursued by predators across broad sweeps of open grasslands, displacing desert, woodland, and browsers.

The higher organic content and water retention of the deeper and richer grassland soils, with long term burial of carbon in sediments, produced a carbon and water vapor sink. This, combined with higher surface albedo and lower evapotranspiration of grassland, contributed to a cooler, drier climate. C ₄ grasses, which are able to assimilate carbon dioxide and water more efficiently than C ₃ grasses, expanded to become ecologically significant near the end of the Miocene between 6 and 7 million years ago. The expansion of grasslands and radiations among terrestrial herbivores correlates to fluctuations in CO ₂.

Cycads between 11.5 and 5 m.y.a. began to rediversify after previous declines in variety due to climatic changes, and thus modern cycads are not a good model for a "living fossil". Eucalyptus fossil leaves occur in the Miocene of New Zealand, where the genus is not native today, but have been introduced from Australia.

Both marine and continental fauna were fairly modern, although marine mammals were less numerous. Only in isolated South America and Australia did widely divergent fauna exist.

In the Early Miocene, several Oligocene groups were still diverse, including nimravids, entelodonts, and three-toed equids. Like in the previous Oligocene epoch, oreodonts were still diverse, only to disappear in the earliest Pliocene. During the later Miocene mammals were more modern, with easily recognizable canids, bears, procyonids, equids, beavers, deer, camelids, and whales, along with now extinct groups like borophagine canids, certain gomphotheres, three-toed horses, and semiaquatic and hornless rhinos like Teleoceras and Aphelops. Islands began to form between South and North America in the Late Miocene, allowing ground sloths like Thinobadistes to island-hop to North America. The expansion of silica-rich C ₄ grasses led to worldwide extinctions of herbivorous species without high-crowned teeth.

A few basal mammal groups endured into this epoch in southern landmasses, including the south american dryolestoid Necrolestes and gondwanathere Patagonia and New Zealand's Saint Bathans Mammal. Non-marsupial metatherians were also still around, such as the American and Eurasian herpetotheriids and peradectids such as Siamoperadectes, and the South American sparassodonts.

Unequivocally recognizable dabbling ducks, plovers, typical owls, cockatoos and crows appear during the Miocene. By the epoch's end, all or almost all modern bird groups are believed to have been present; the few post-Miocene bird fossils which cannot be placed in the evolutionary tree with full confidence are simply too badly preserved, rather than too equivocal in character. Marine birds reached their highest diversity ever in the course of this epoch.

Approximately 100 species of apes lived during this time, ranging throughout Africa, Asia and Europe and varying widely in size, diet, and anatomy. Due to scanty fossil evidence it is unclear which ape or apes contributed to the modern hominid clade, but molecular evidence indicates this ape lived between 7 and 8 million years ago. The first hominins ( bipedal apes of the human lineage) appeared in Africa at the very end of the Miocene, including Sahelanthropus, , and an early form of Ardipithecus ( A. kadabba) The chimpanzee-human divergence is thought to have occurred at this time.

The expansion of grasslands in North America also led to an explosive radiation among snakes. Previously, snakes were a minor component of the North American fauna, but during the Miocene, the number of species and their prevalence increased dramatically with the first appearances of vipers and elapids in North America and the significant diversification of Colubridae (including the origin of many modern genera such as Nerodia, Lampropeltis, Pituophis and Pantherophis).

In the oceans, brown algae, called kelp, proliferated, supporting new species of sea life, including otters, fish and various invertebrates.

Cetaceans attained their greatest diversity during the Miocene, with over 20 recognized genera in comparison to only six living genera. This diversification correlates with emergence of gigantic macro-predators such as megatoothed sharks and raptorial sperm whales. Prominent examples are C. megalodon and L. melvillei. Other notable large sharks were C. chubutensis, Isurus hastalis, and Hemipristis serra.

Crocodilians also showed signs of diversification during Miocene. The largest form among them was a gigantic caiman Purussaurus which inhabited South America. Another gigantic form was a false gharial Rhamphosuchus, which inhabited modern age India. A strange form, Mourasuchus also thrived alongside Purussaurus. This species developed a specialized filter-feeding mechanism, and it likely preyed upon small fauna despite its gigantic size.

The pinnipeds, which appeared near the end of the Oligocene, became more aquatic. Prominent genus was Allodesmus. A ferocious walrus, Pelagiarctos may have preyed upon other species of pinnipeds including Allodesmus.

Furthermore, South American waters witnessed the arrival of Megapiranha paranensis, which were considerably larger than modern age piranhas.

New Zealand's Miocene fossil record is particularly rich. Marine deposits showcase a variety of cetaceans and penguins, illustrating the evolution of both groups into modern representatives. The early Miocene Saint Bathans Fauna is the only Cenozoic terrestrial fossil record of the landmass, showcasing a wide variety of not only bird species, including early representatives of clades such as moas, kiwis and adzebills, but also a diverse herpetofauna of sphenodontians, crocodiles and turtle as well as a rich terrestrial mammal fauna composed of various species of bats and the enigmatic Saint Bathans Mammal.

There is evidence from oxygen isotopes at Deep Sea Drilling Program sites that ice began to build up in Antarctica about 36 Ma during the Eocene. Further marked decreases in temperature during the Middle Miocene at 15 Ma probably reflect increased ice growth in Antarctica. It can therefore be assumed that East Antarctica had some glaciers during the early to mid Miocene (23-15 Ma). Oceans cooled partly due to the formation of the Antarctic Circumpolar Current, and about 15 million years ago the ice cap in the southern hemisphere started to grow to its present form. The Greenland ice cap developed later, in the Middle Pliocene time, about 3 million years ago.

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The Miocene is the first epoch of the Neogene period of the Cainozoic. It started about 23 million years ago and ended about 5.33 million years ago. The rock beds that mark the start and end are well known, but the exact dates of the start and end of the period are uncertain.

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The Pliocene ( Pleiocene in older texts) was a short geological epoch at the end of the Neogene. It began 5.3 million years ago (mya), and ended 2.6 mya. The Pliocene follows the Miocene and is followed by the Pleistocene.

The world continued to get cooler and drier in the Pliocene. Tropical rain forests and deciduous forests shrank. Grasslands grew, and many herbivorous mammals became grazers instead of browsers. Hominid evolution took a new turn as some apes started to live on the savannah instead of the forests ( Australopithecines).

Images for kids

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The Pliocene ( Pleiocene in older texts) was a short geological epoch at the end of the Neogene. It began 5.3 million years ago (mya), and ended 2.6 mya. The Pliocene follows the Miocene and is followed by the Pleistocene. The world continued to get cooler and drier in the Pliocene.

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The Quaternary is the current geological period. It is the most recent of the three periods of the Cainozoic era and the most recent of the twelve periods of the current eon, the Phanerozoic. The Quaternary follows the Neogene, which is the second period of the Cainozoic.

The Quaternary began about 2.6 million years ago, and continues today. A great deal of information is considered when geologists discuss the timing of periods. The status of the Quaternary as a period is confirmed by the International Commission on Stratigraphy (ICS).

In the Quarternary were the glaciations known as the Ice Age. Also, anatomically modern humans evolved. During the Quaternary, many large mammalian species became extinct. This was due to climate change and hunting by humans.

The Quaternary includes two geologic epochs:

References

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The Quaternary is the current geological period. It is the most recent of the three periods of the Cainozoic era and the most recent of the twelve periods of the current eon, the Phanerozoic. The Quaternary follows the Neogene, which is the second period of the Cainozoic.

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The term is most used for the Pleistocene megafauna - the large land animals of the last ice age, such as mammoths. It is also used for the largest living wild land animals, especially elephants, giraffes, hippopotamus, rhinoceros, elk, condors, etc.

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Human evolution is about the origin of human beings. All humans belong to the same species, which has spread from its birthplace in Africa to almost all parts of the world. Its origin in Africa is proved by the fossils which have been found there.

The term 'human' in this context means the genus Homo. However, studies of human evolution usually include other hominids, such as the Australopithecines, from which the genus Homo had diverged (split) by about 2.3 to 2.4 million years ago in Africa. The first Homo sapiens, the ancestors of today's humans, evolved around 200,000 years ago.

It was known for centuries that man and the apes were related. At heart, their anatomy is similar, despite many superficial differences. This was the reason why Buffon and Linnaeus, in the 18th century, put them together in one family. Charles Darwin's theory of evolution says that such basic structural similarity comes from the common origin of the group. The apes and man are close relatives, and are primates: the order of mammals which includes monkeys, apes, lemurs and tarsiers.

The great apes live in tropical rainforests. It is thought that human evolution started when a group of apes (now called the australopithecines) began to live more in the savannah. A savannah is more open, with trees, shrubs and grass. This group started walking on two legs. They began to use their hands to carry things. Life in the open was different, and there was a big advantage in having better brains. Their brains grew larger, and they began to make simple tools. This process began at least 5 million years ago. We have fossils of two or three different groups of walking apes, and one was the ancestor of humans.

The biological name for "human" or "man" is Homo. The modern human species is called Homo sapiens. "Sapiens" means "thought". Homo sapiens means "the thinking man".

Paleoanthropology looks at ancient human fossils, tools, and other signs of early human life. It began in the 19th century with the discovery of a skull of " Neanderthal man" in 1856.

Humans are similar to great apes

By 1859, zoologists had known for a long time that humans are, in their anatomy, similar to the great apes. There are also differences: humans can speak, for example. But the similarities are more basic than the differences. Humans also have features with a much older history, from early in the life of vertebrates.

The idea that species are caused by evolution had been proposed before Darwin, but his book gave much evidence, and many were persuaded by it. The book was On the Origin of Species by means of Natural Selection, published in November 1859. In this book, Darwin wrote about the idea of evolution in general, rather than the evolution of humans. Light will be thrown on the origin of man and his history, was all Darwin wrote on the subject. Nevertheless, the implication of the theory was clear to readers at the time.

Several people discussed the evolution of humans. Among them were Thomas Huxley and Charles Lyell. Huxley convincingly showed many of the similarities and differences between humans and apes in his 1863 book Evidence as to Man's Place in Nature. When Darwin published his own book on the subject, The Descent of Man, and selection in relation to sex, the idea of human evolution was already well-known. The theory was controversial. Even some of Darwin's supporters (such as Alfred Russel Wallace and Charles Lyell) did not like the idea that human beings have evolved their impressive mental capacities and moral sensibilities through natural selection.

Since the 18th century, scientists thought the great apes to be closely related to human beings. In the 19th century, they speculated that the closest living relatives of humans were either chimpanzees or gorillas. Both live in central Africa in tropical rainforests. In fact, chimpanzees are closest to us. Biologists believed that humans share a common ancestor with other African great apes and that fossils of these ancestors would be found in Africa, which they have been. It is now accepted by virtually all biologists that humans are not only similar to the great apes, but actually are great apes.

The issue was confirmed by late 20th century studies on the sequences of proteins and genes in apes and man. These studies showed that man shares about 95 to 98% of these structures with chimpanzees. This is a much closer relationship than with any other type of animal, and fully supports the ideas put forward in the 19th century by Darwin and Huxley.

"Currently available genetic and archaeological evidence is generally interpreted as supportive of a recent single origin of modern humans in East Africa. However, this is where the near consensus on human settlement history ends, and considerable uncertainty clouds any more detailed aspect of human colonization history".

Distinguishing features

Primates have diversified in habitats such as trees and bushes. They have many features which are adaptations to their environment. Here are some of those traits:

Shoulder joints which allow high degrees of movement in all directions.

Nails on the fingers and toes (in most species).

Sensitive tactile pads on the ends of the digits.

Sockets of eyes encircled in bone.

A complex visual system with binocular (stereoscopic) vision, high visual acuity and color vision.

Brain large in comparison to body size, especially in simians (old world monkeys and apes).

Enlarged cerebral cortex (brain): learning, problem solving.

Reduced number of teeth compared to primitive mammals;.

Typically one young per pregnancy.

Not all primates have these anatomical traits, nor is every trait unique to primates. Primates are frequently highly social, live in groups with 'flexible dominance hierarchies'.

Other similarities

Closely related animals almost always have closely related parasites. This usually comes about because parasites evolve with their hosts, and when host populations split, their parasites split also. It is also possible for parasites to get from one species to another. Two of the most serious parasitic infections of humans in Africa have originated in apes. Each may have been transferred to humans by a single cross-species event.

There are several species of mosquito, and several species of the malarial parasite Plasmodium. The most serious type, P. falciparum, which kills many millions of people each year, originated in gorillas. It is now virtually certain that chimpanzees are the source of HIV-1, the major cause of AIDS. This information is got by the sequence analysis of ape and human viruses.

The relevance of this to evolution is that our physiology is so close to the apes that their parasites were able to transfer to humans with great success. Humans have much less resistance to these parasites, which are ancient in origin, but comparatively new to our species.

Immediate ancestors of the genus Homo

It was not until the 1920s that hominid fossils were discovered in Africa. In 1924, Raymond Dart described Australopithecus africanus. The specimen was called the Taung Child, an australopithecine infant discovered in a cave deposit being mined for concrete at Taung, South Africa. The remains were a remarkably well-preserved tiny skull and a cast of the inside of the individual's skull. Although the brain was small (410 cm³), its shape was rounded, unlike that of chimpanzees and gorillas, and more like a modern human brain. Also, the specimen had short canine teeth, and the position of the foramen magnum was evidence of bipedal locomotion. All of these traits convinced Dart that the Taung baby was a bipedal human ancestor, a transitional form between apes and humans.

It took another 20 years before Dart's claims were taken seriously. This was after other similar skeletons had been found. The most common view of the time was that a large brain evolved before bipedality, the ability to walk on two feet more or less upright. It was thought that intelligence similar to that of modern humans was necessary for bipedalism. This turned out to be wrong: bipedality came first.

The australopithecines are now thought to be immediate ancestors of the genus Homo, the group to which modern humans belong. Both australopithecines and Homo sapiens are part of the tribe Hominini, but recent data has brought into doubt the position of A. africanus as a direct ancestor of modern humans; it may well have been a cousin. The australopithecines were originally classified as either gracile or robust. The robust variety of Australopithecus has since been reclassified as Paranthropus, although it is still regarded as a subgenus of Australopithecus by some authors.

In the 1930s, when the robust specimens were first described, the Paranthropus genus was used. During the 1960s, the robust variety was moved into Australopithecus. The recent trend has been back to the original classification as a separate genus.

It was Carolus Linnaeus who chose the name Homo. Today, there is only one species in the genus: Homo sapiens. There were other species, but they became extinct.

The figure shows where some of them lived and at what time. Some of the other species might have been ancestors of H. sapiens. Many were likely our "cousins", they developed away from our ancestral line.

Anthropologists are still investigating the exact line of descent. A consensus on which should count as separate species and which as subspecies has not been reached yet. In some cases this is because there are very few fossils, in other cases it is due to the slight differences used to classify species in the Homo genus.

The evolution of the genus Homo took place mostly in the Pleistocene. The whole genus is characterised by its use of stone tools, initially crude, and becoming ever more sophisticated. So much so that in archaeology and anthropology the Pleistocene is usually referred to as the Palaeolithic, or the Stone Age.

Homo habilils was likely the first species of Homo. It developed from the Australopithecus, about 2.5 million years ago. It lived until about 1.4 million years ago. It had smaller molars (back teeth) and larger brains than the Australopithecines.

There are two proposed species that lived from 1.9 to 1.6 million years ago. Their relation has not been clarified. One of them is called Homo rudolfensis. It is known from a single incomplete skull from Kenya. Scientists have suggested that this was just another habilis, but this has not been confirmed. The other is currently called Homo georgicus. It is from Georgia and may be an intermediate form between H. habilis and H. erectus, or a sub-species of H. erectus.

Homo erectus was first discovered on the island of Java in Indonesia, in 1891. The discoverer, Eugene Dubois originally called it Pithecanthropus erectus based on its morphology that he considered to be intermediate between that of humans and apes. Homo erectus lived from about 1.8 million to 70,000 years ago. The earlier specimens (from 1.8 to 1.2 million years ago) are sometimes seen as a different species, or a subspecies. called Homo ergaster, or Homo erectus ergaster'.

In the early Pleistocene, 1.5-1 mya, in Africa, Asia, and Europe, presumably, some populations of Homo habilis evolved larger brains and made more elaborate stone tools; these differences and others are sufficient for anthropologists to classify them as a new species, . In addition H. erectus was the first human ancestor to walk truly upright. This was made possible by the evolution of locking knees and a different location of the foramen magnum (the hole in the skull where the spine enters). They may have used fire to cook their meat.

A famous example of Homo erectus is Peking Man; others were found in Asia (notably in Indonesia), Africa, and Europe. Many paleoanthropologists are now using the term Homo ergaster for the non-Asian forms of this group. They reserve H. erectus only for those fossils found in the Asian region that meet certain requirements (as to skeleton and skull) which differ slightly from ergaster.

Neanderthal Man

Homo neaderthalensis (usually called Neanderthal man) lived from about 250,000 to about 30,000 years ago. Also, less usual, as Homo sapiens neanderthalensis: there is still some discussion if it was a separate species Homo neanderthalensis, or a subspecies of H. sapiens. While the debate remains unsettled, evidence from mitochondrial DNA and Y-chromosomal DNA sequencing indicates that little or no gene flow occurred between H. neanderthalensis and H. sapiens, and, therefore, the two were separate species. In 1997, Dr. Mark Stoneking, then an associate professor of anthropology at Pennsylvania State University, stated:

"These results [based on mitochondrial DNA extracted from Neanderthal bone] indicate that Neanderthals did not contribute mitochondrial DNA to modern humans... Neanderthals are not our ancestors".

More investigation of a second source of Neanderthal DNA supported these findings.

A third species

A genetic analysis of a piece of finger bone found in Siberia has produced a surprise result. It dates to about 40,000 years ago, at a time when Neanderthals and modern man were living in the area. German researchers found its mitochondrial DNA did not match either that of our species or that of Neanderthals. If this result is correct, the bone belongs to a previously unknown species. The degree of difference in the DNA suggests this species split off from our family tree about a million years ago, well before the split between our species and Neanderthals.

Homo floresiensis, which lived about 100,000-12,000 years ago has been nicknamed for its small size. Its size may be a result of island dwarfism, the tendency for large mammals to evolve smaller forms on islands. H. floresiensis is intriguing both for its size and its age. It is a concrete example of a recent species of the genus Homo that shows derived traits not shared with modern humans. In other words, H. floresiensis share a common ancestor with modern humans, but split from the modern human lineage and followed a different evolutionary path. The main find was a skeleton believed to be a woman of about 30 years of age. Found in 2003 it has been dated to approximately 18,000 years old. The living woman was estimated to be one meter in height, with a brain volume of just 380 cm ³ This is small for a chimpanzee and less than a third of the H. sapiens average of 1400 cm ³.

There is an ongoing debate over whether H. floresiensis is indeed a separate species. Some scientists believe that H. floresiensis was a modern H. sapiens suffering from pathological dwarfism. Modern humans who live on Flores, the island where the skeleton was found, are pygmies. This fact is consistent with either theory. One line of attack on H. floresiensis is that it was found with tools only associated with H. sapiens.

Human arrival on Flores

Stone artefacts have now been found on Flores which can be dated to a million years ago. These artefacts are proxies; which means there were no skeletons of humans, but only a species of Homo could have made the artefacts. The artefacts are flakes and other implements, 48 in all, some of which show signs of being worked to produce a cutting edge. This means that humans were present on Flores by that date, but it does not tell us which species that was.

Homo sapiens has lived from about 250,000 years ago to the present. Between 400,000 years ago and the second warm period in the Middle Pleistocene, around 250,000 years ago, its skull grew and more sophisticated technologies based on stone tools developed. One possibility is that a transition between H. erectus to occurred. The evidence of Java Man suggests there was an initial migration of H. erectus out of Africa. Then, much later, a further development of H. sapiens from H. erectus in Africa. Then a subsequent migration within and out of Africa eventually replaced the earlier H. erectus.

Out of Africa

Studies of the human genome, especially the Y- chromosome DNA and mitochondrial DNA, have supported a recent African origin. Evidence from autosomal DNA also supports the recent African origin. The details of this great saga are not fully established yet, but by about 90,000 years ago they had moved into Eurasia and the Middle East. This was the area where Neanderthals, Homo neanderthalensis, had been living for a long time (at least 500,000 years in western Europe).

By about 42 to 44,000 years ago Homo sapiens had reached western Europe, including Britain. In Europe and western Asia, Homo sapiens replaced the Neanderthals by about 35,000 years ago. The details of how this happened are not known.

At roughly the same time Homo sapiens arrived in Australia (However a recent archaeological dig in Kakadu, Northern Territory, may suggest Homo sapiens arrived in Australia 65,000 years ago). Their arrival in the Americas was much later, about 15,000 years ago. All these earlier groups of modern man were hunter-gatherers.

Current research has established that human beings are genetically rather homogenous (similar). The DNA of individuals is more alike than usual for most species. This may have resulted from their relatively recent evolution or from the Toba catastrophe. Distinctive genetic have arisen as a result of small groups of people moving into new environmental circumstances. These adapted traits are a very small component of the Homo sapiens genome and include such outward 'racial' characteristics as skin color and nose shape, and internal characteristics such as the ability to breathe more efficiently at high altitudes.

H. sapiens idaltu, from Ethiopia, about 160,000 years ago, is a proposed subspecies. It is the oldest known anatomically modern human.

Species list

This list is in chronological order by genus.

Related pages

References

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2. Caro-Beth Stewart and Todd R Disotell (1998). . "Primate evolution - in and out of Africa". Current Biology 8 (16)http://www.cell.com/current-biology/retrieve/pii/S0960982207003673.

3. Ian Tattersall (2009). . "Human origins: Out of Africa". Proc Natl Acad Sci U S A. 106 (36)http://www.pnas.org/content/106/38/16018.short.

4. Stringer C.B. (1994). "Evolution of early humans". In Steve Jones, Robert Martin & David Pilbeam (eds). The Cambridge Encyclopedia of Human Evolution. Cambridge: Cambridge University Press. p. 242. . Also ISBN 978-0-521-46786-5 (paperback)

5. McHenry H.M (2009). "Human Evolution". In Michael Ruse & Joseph Travis. Evolution: the first four billion years. Cambridge, Massachusetts: Harvard University Press. p. 265. .

6. O'Neil, Dennis. . "Evolution's past is modern human's present". Behavioral Sciences Department, Palomar College, San Marcos, Californiahttp://anthro.palomar.edu/homo2/mod_homo_4.htm.

7. Shubin, Neil 2009. Your inner fish: the amazing discovery of our 375-million year-old ancestor. Penguin, London.

8. . Darwin, Charles (1861). On the Origin of Species (3rd ed.). London: John Murray. pp. 488http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=side&pageseq=506.

9. Ajit, Varki & Nelson, David L (2007). . "Genomic comparisons of humans and chimpanzees" (PDF). Annual Review of Anthropology (Palo Alto, CA: Annual Reviews) 36: 191-209. doi:http://www.chd.ucsd.edu/_files/fall2008/Varki.2007.ARA.pdf. "Sequence differences from the human genome were confirmed to be ∼1% in areas that can be precisely aligned, representing ∼35 million single base-pair differences. Some 45 million nucleotides of insertions and deletions unique to each lineage were also discovered, making the actual difference between the two genomes ∼4%.".10.1146/annurev.anthro.36.081406.094339 .

10. Hua Liu & others 2006. A geographically explicit genetic model of worldwide human-settlement history. The American Journal of Human Genetics. 79, 230-237.

11. phrase means something like: 'who is the leader may change according to the activity of the group'

12. White T. & Kazlev A. (2006-01-08). . "Archonta: Primates". Palaeoshttp://www.palaeos.com/Vertebrates/Units/480Archonta/480.400.html#Primates.

13. Price P.W. 1980. Evolutionary biology of parasites. Princeton N.J.

14. Keefe B.E. & others 2006. Chimpanzee reservoirs of pandemic and non-pandemic HIV-1. Science 313, 523-526.

15. The foramen magnum is where the spine joins the skull. In apes, the skull in life tilts forward, but in humans it is more evenly balanced on top of the spine. During human evolution, the position of the foramen magnum moved towards the middle underside the skull.

16. Klein, Richard G. 2009. The human career: human biological and cultural origins. 3rd ed, Chicago.

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# data[].attributes.attachment_link.description
Human evolution is about the origin of human beings. All humans belong to the same species, which has spread from its birthplace in Africa to almost all parts of the world. Its origin in Africa is proved by the fossils which have been found there. The term 'human' in this context means the genus Homo.