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~4.5 Billion Years Ago, Beginning of the solar system, the creation of early earth

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~4.5 Billion Years Ago, Beginning of the solar system, the creation of early earth

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Our solar system formed around 4.5 billion years ago from an interstellar cloud that began to clump together due to gravity. This cloud went through a series of phases before the planets, such as earth, and stars were created.

Earth formed with 3 main layers, the core, the mantle, and the crust. Its original atmosphere was made of gases such as hydrogen and helium, making the atmosphere very warm. After Earth cooled and led to the creation of the sea, it soon filled with other gases such as methane and carbon dioxide that came from volcanic activity.

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~4.6 Billion - 540 Million Years Ago,  Eon: Proterozoic

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~4.6 Billion - 540 Million Years Ago,  Eon: Proterozoic

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Proterozoic Era
Precambrian Period

During the Precambrian, simple anaerobic life appeared, followed by  photosynthetic forms that added oxygen to the atmosphere.

There was  the Huronian ice age that lasted from ~2.4 - 2.1 billion years ago.
There was also the Cryogenian ice age (snowball earth) which occurred from ~850 to 635 million years ago and covered Earth with ice sheets that could've even reached the equator.

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~2.7 Billion Years Ago, Appearance of cyanobacteria

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~2.7 Billion Years Ago, Appearance of cyanobacteria

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Cyanobacteria are photosynthetic prokaryotic organisms that emit oxygen as a result of taking in carbon dioxide. They were probably one of the only organisms that created oxygen during this time and were found in oceans with other microbes. This meant that oceans had high concentrations of oxygen. It wouldn't be until a few hundred million years later that the oxygen would enter the atmosphere.

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~2.4 billion years - 600 million years ago, Oxygen enters the atmosphere, the creation of the ozone layer

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~2.4 billion years - 600 million years ago, Oxygen enters the atmosphere, the creation of the ozone layer

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Oxygen entered the atmosphere and began to build up after all dissolved iron was gone. Dissolved iron took in oxygen as it increased and settled on the ocean floor which created red-colored sedimentary rocks.

As oxygen levels increased, carbon dioxide and methane levels decreased which significantly cleared up the sky. This eventually led to the creation of the ozone layer that formed as UV rays split oxygen molecules.

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~1.2 Billion Years Ago, First multi-cellular organisms

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~1.2 Billion Years Ago, First multi-cellular organisms

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Multicellular forms evolved around 1.2 billion years ago, although the oldest known fossil for multicellular organisms date back to around 700 million years ago. They have  descendants such as multicellular algae, plants, fungi, and animals. Almost every organism large enough to see with the naked eye is
multicellular.

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~540 - 490 Million Years Ago, Eon: Phanerozoic 

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~540 - 490 Million Years Ago, Eon: Phanerozoic 

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Paleozoic Era
Cambrian Period

First known animals began to evolve, such as jellyfish and sponges.

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 ~540 Million Years Ago, Appearance of invertebrates

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 ~540 Million Years Ago, Appearance of invertebrates

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Invertebrates are usually organisms that lack a backbone such as jellyfish and sponges. They first appeared around 540 million years ago.

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~500 Million Years Ago, Appearance of the first plants

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~500 Million Years Ago, Appearance of the first plants

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Some of the first-known land plants appeared around 500 million years ago and could've possibly photosynthesized.

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~490 - 440 Million Years Ago, Eon: Phanerozoic 

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~490 - 440 Million Years Ago, Eon: Phanerozoic 

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Paleozoic Era
Ordovician Period

The first vertebrates appeared during this time, and marine life flourished.

Around 440 million years ago, there was a mass extinction that wiped out a large percentage of organisms.

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~480 Million Years Ago, Appearance of first insects

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~480 Million Years Ago, Appearance of first insects

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Insects are terrestrial arthropods that evolved from the first land dwellers, other arthropods, like lobsters, crabs, spiders, and scorpions.

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~460 Million Years Ago, Appearance of fungi

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~460 Million Years Ago, Appearance of fungi

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Early fungi had first appeared around 1 billion years ago, and were observed to be aquatic. Terrestrial fungi, however, has only appeared around 460 million years ago.

Early plants and fungi had a biological partnership called mycorrhizae and mutualism which allowed them to survive on land.

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~450 Million Years Ago, Appearance of the first vertebrates

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~450 Million Years Ago, Appearance of the first vertebrates

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Vertebrates are organisms that have backbones, such as humans and almost all other fairly large land animals. They first appeared around 450 million years ago.

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~440 - 420 Million Years Ago, Eon: Phanerozoic 

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~440 - 420 Million Years Ago, Eon: Phanerozoic 

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Paleozoic Era
Silurian Period

Similar to the ordovician period, the silurian period was a time where marine life flourished and evolved.

One main event was the Andean-Saharan ice age, which occurred between ~460 - 430 million years ago.

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~420 - 360 Million Years Ago, Eon: Phanerozoic 

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~420 - 360 Million Years Ago, Eon: Phanerozoic 

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Paleozoic Era
Devonian Period

There was a lot of marine competition during this period. Animals, such as arthropods, began to invade the land.

There was a mass extinction around 360 million years ago, near the end of the devonian period, where many animals died.

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~370 Million Years Ago, Appearance of amphibians 

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~370 Million Years Ago, Appearance of amphibians 

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Amphibians first inhabited the land around 370 million years ago. They have several structural changes, such as lungs, which allowed them to survive as they adapted to land. Some types of amphibians include animals from today such as frogs, toads, and salamanders.

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~360 Million Years Ago, First land animals

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~360 Million Years Ago, First land animals

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Although amphibians adapted well enough to land, they weren't as suited for the drier environment. Land animals evolved from amphibians.

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~360 - 320 Million Years Ago, Eon: Phanerozoic 

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~360 - 320 Million Years Ago, Eon: Phanerozoic 

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Paleozoic Era
Mississippian Period

The Mississippian period, also known as a part of the Carboniferous period, was a time where insects had evolved and was dominated by arthropods.

One main event was the Karoo ice age that lasted around 100 million years and occured between ~360 to 260 million years ago.

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~340 Million Years Ago, Appearance of reptiles

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~340 Million Years Ago, Appearance of reptiles

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Reptiles evolved from their amphibian ancestors and include animals from today, such as snakes, lizards, and turtles. They were better suited for the drier environment compared to amphibians and were also able to lay their eggs on dry land unlike amphibians.

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~320 - 300 Million Years Ago, Eon: Phanerozoic 

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~320 - 300 Million Years Ago, Eon: Phanerozoic 

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Paleozoic Era
Pennsylvanian Period

The Pennsylvanian period, also known as part of the Carboniferous period, was a time where the amniotic egg evolved, which allowed for more successful reproduction among land animals.

One main event during this time was also Karoo ice age.

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~300 - 250 Million Years Ago, Eon: Phanerozoic 

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~300 - 250 Million Years Ago, Eon: Phanerozoic 

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Paleozoic Era
Permian Period

A mass extinction occurred both on land and on sea.  Around 95% of all life forms perished during the Permian Period.

The Karoo ice age was also still going on during this time.

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~250 - 200 Million Years Ago, Eon: Phanerozoic  

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~250 - 200 Million Years Ago, Eon: Phanerozoic  

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Mesozoic Era
Triassic Period

Organisms that survived the Permian extinction, such as reptiles, became more prominent.

There was a mass extinction that occurred around 200 million years ago that killed around 80% of all life forms.

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~230 Million Years Ago, Appearance of dinosaurs 

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~230 Million Years Ago, Appearance of dinosaurs 

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Dinosaurs are a group of diverse reptiles. Like most large animals, they're vertebrates. They first appeared around 230 million years ago and became dominant vertebrates on land.

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~210 Million Years Ago, Appearance of mammals

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~210 Million Years Ago, Appearance of mammals

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Around 210 million years ago, while dinosaurs were still around, therapsids, reptiles with complex teeth and legs positioned beneath their body, gave rise to mammals.

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~200 - 145 Million Years Ago, Eon: Phanerozoic 

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~200 - 145 Million Years Ago, Eon: Phanerozoic 

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Mesozoic Era
Jurassic Period

Dinosaurs ruled during this time, birds began to evolve, and early mammals began to diversify.

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~150 Million Years Ago, Appearance of birds

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~150 Million Years Ago, Appearance of birds

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Birds first appeared around 150 million years ago and were thought to have evolved from feathered dinosaurs.

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~145 - 65 Million Years Ago, Eon: Phanerozoic 

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~145 - 65 Million Years Ago, Eon: Phanerozoic 

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Mesozoic Era
Cretaceous Period

Flowering plants appeared during the Cretaceous. Many modern insects, such as ants and butterflies, began to develop.

There was a mass extinction that occurred around 65 million years ago. It was responsible for eliminating around 80% of all species including dinosaurs.

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~130 Million Years Ago, Appearance of flowering plants

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~130 Million Years Ago, Appearance of flowering plants

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Flowering plants first appeared around 130 million years ago. Through time, they eventually became important to many different organisms.

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~65 - 2.6 Million Years Ago, Eon: Phanerozoic 

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~65 - 2.6 Million Years Ago, Eon: Phanerozoic 

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Cenozoic Era
Tertiary Period

During this time, grasses evolved and supported grazing animals, mammals were able to reproduce more successfully with the absence of dinosaurs, and birds also diversified into some of the many birds we see today.

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~5 to 7 Million Years Ago, Appearance of early humans

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~5 to 7 Million Years Ago, Appearance of early humans

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The first humans appeared around 5 to 7 million years ago in Africa and eventually evolved into homosapiens, what we are now.

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~2.6 Million Years Ago - Present, Eon: Phanerozoic 

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~2.6 Million Years Ago - Present, Eon: Phanerozoic 

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Cenozoic Era
Quaternary Period

This is the current period that we live in. A series of ice ages, such as the quaternary ice age (which is an interglacial ice age still going on today), occurred. Earth’s climate began to warm about 20,000 years ago, glaciers melted, and sea levels rose.