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Red: Era
Orange: Events
Green: Period
Blue: Eon
Purple: Appearances
White: Time, Ice Ages

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4.6 Billion Years Ago
- Nearly 90% of Earth’s history occurred during the Precambrian. Simple anaerobic life appeared, followed by photosynthetic forms, which added oxygen to the atmosphere.

- Precambrian simply means “everything before the Cambrian Era”. There are actually three eras in the Precambrian: the Hadean, the Archaean, and the Proterozoic. The three eras are grouped together in what is known as the Precambrian Era.

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4.6 Billion Years Ago
- It began with the formation of the Earth about 4.6 billion years ago and ended 4 billion years ago. It is the very first eon that falls under the Precambrian Era.

- Throughout part of the eon, impacts from extraterrestrial bodies released enormous amounts of heat that likely prevented much of the rock from solidifying at the surface.

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4.5 Billion Years Ago
- It all began with a dense cloud of gas and dust. As this cloud collapsed presumably from a supernova, its shockwave caused it to spin leading us to the first phase of our solar system, spinning. As each atom moved, they attached to others due to gravity. All of this moving energy averaged out in one direction. This caused the solar system to spin.

- The second phase is flattening. Gravity pulled the dust and gas closer to the center, and this made the solar system spin more rapidly.

- The third phase are planetesimals. Gas and dust came together due to gravity forming planetesimals. Because of their greater gravity, the largest planetesimals collected the most material.

- The fourth and final phase are planets. Smaller planetesimals collided with the larger ones, and the planets grew. The remaining dust and gas were gradually pulled in, leaving the Sun and the planets behind.

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4.5 Billion Years Ago
- The planet was bombarded by huge rock bodies left over from the formation of the solar system. The impacts were colossal; one of them may have
dislodged a chunk of Earth that became the moon.

-During this period of bombardment, the pounding generated enough
heat to vaporize all the available water and prevent seas from
forming.

- About half a billion years later, earth solidified enough to contain water.

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4 Billion Years Ago
- The second eon of four, and at the time Earth's crust had cooled enough for continents to form, and for life to start.

- Life was fairly simple throughout this eon, mostly represented by shallow-water microbial mats called stromatolites, and the atmosphere lacked free of oxygen.

- Abundance of trilobites, brachiopods, gastropods, and so much more engulfed the waters during this eon.

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3.5 Billion Years Ago
- Before photosynthesis evolved, Earth's atmosphere had no free oxygen. Oxygen was first produced by photosynthetic prokaryotic organisms called cyanobacteria that used the abundant carbon dioxide in the atmosphere and emitted oxygen as a waste product into the waters of the oceans.

- These organisms lived even before the first buildup of oxygen in the atmosphere, probably as early as 3.5 billion years ago.

- These organisms are mostly found in tidal flats, where the organic carbon that they produced were buried. Mats of cyanobacteria trapped and bound sediments, forming stromatolites that mark the presence of microbial colonies.

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3.5 Billion Years Ago
- The first invertebrates developed in the oceans. They were soft-bodied animals with a shell, such as trilobites.

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2.5 Billion Years Ago
- The third eon of four, and modern plate tectonics became active. Ancient cores of the continents moved over wide areas of the earth, accumulating smaller fragments of crust, sometimes colliding with other large landmasses.

- Bacteria and blue-green algae as well as the first oxygen-dependent animals, the Ediacara fauna, were seen during this time period.

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2.4 Billion Years Ago
- The Huronian ice age was caused by the saturation of the new gas oxygen in the air and waters, Earth progressively cooler despite the Sun increasing in brightness as it aged.

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The Appearance of Oxygen in the Atmosphere

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The Appearance of Oxygen in the Atmosphere

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2.3 Billion Years Ago
- Scientists think that algae that first evolved 2.7 billion years ago, and soon after this oxygen began to exist in the atmosphere.

- Photosynthesis by primitive plants and algae released oxygen, which gradually built up in the atmosphere.

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720 Million Years Ago
- This time period was a time when icy deserts dominated the Earth.

- It was the second-last geological period of the Proterozoic Aeon, which ended 541 million years ago with the Cambrian Explosion.

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710 Million Years Ago
- The main evidence of the severity of these events comes from geological evidence of glaciers near the equator.

- Evidence suggests that the consecutive global ice ages set the stage for the subsequent explosion of complex, multicellular life on Earth.

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600 Million Years Ago
- During this time, a thin ozone layer formed that was capable of protecting life from harmful wavelengths of UV radiation

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The Appearance of the First Multicellular Organisms

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The Appearance of the First Multicellular Organisms

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600 Million Years Ago
- Large, multicellular life forms may have appeared on Earth one billion years earlier than was previously thought. Macroscopic multicellular life had been dated to around 600 million years ago

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544 Million Years Ago
- Early on, the fossil record became rich with evidence of many types of highly diverse marine life.

- It was when the well known "Cambrian explosion" occurred, signifying the vast majority of marine life present at this time. This explosion also included the evolution of arthropods, ancestors of today's insects and crustaceans, and chordates, animals with rudimentary spinal cords.

- This era contains six periods: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.

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544 Million Years Ago
- In this time period, it produced the most intense burst in evolution ever known, calling it the "Cambrian Explosion". The event was described by the appearance of many of the major phyla that make up modern day animals we see today.

- The first known animals began to evolve, such as jellyfish and sponges.

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541 Million Years Ago
- The fourth and final eon which ranges from 541 million years ago until now, and the one during which abundant animal and plant life has existed.

- It began with the Cambrian Period when animals first developed hard shells preserved in the fossil record.

- The Phanerozoic is divided into three eras: the Paleozoic, Mesozoic, and Cenozoic, which is further divided to the 12 periods.

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525 Million Years Ago
- Vertebrates originated about 525 million years ago during the Cambrian explosion, which saw a rise in diversity among organisms.

- The earliest vertebrates were jawless fish, similar to living hagfish.

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505 Million Years Ago
- This period started at a major extinction event called the Cambrian-Ordovician extinction events about 484.4 million years ago.

- During this time, ancestors of modern octopi and squid formed. The first vertebrates appeared, among them being jawless fishes. The ocean was filled to the brim with marine life, and there was lots of competition as well.

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479 Million Years Ago
- Researchers' phylogenetic data indicates that the largest group of insects, hexapoda, may have evolved even earlier, around 479 million years ago, during the Early Ordovician Period.

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470 Million Years Ago
- The first land plants appearedd around 470 million years ago, during the Ordovician period when life was diversifying rapidly.

- They were non-vascular plants, like mosses and liverworts, that didn't have deep roots.

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460 Million Years Ago
- The Andean-Saharan ice age lasted 30 million years during the Ordovician and Silurian periods.

- What happened during this time period was volcanic activity and weathering related to extensive mountain building caused carbon dioxide levels to plummet, chilling the planet.

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450 Million Years Ago
- Based on fossil evidence, fungi appeared in the Precambrian era.

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450 Million Years Ago
- Collectively the second-largest of the five major extinction events in Earth's history in terms of percentage of genera that became extinct.

- The extinction was a most likely a result of global cooling and reduced sea levels, which dramatically impacted the many marine species living in warm, shallow coastal waters.

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440 Million Years Ago
- Same as the Ordovician period, ancestors of modern octopi and squid formed, the first vertebrates appeared, and there was lots of undertakings happening in the ocean during this time

- Continental landmasses were low and sea levels were rising. This meant rich shallow sea ecosystems with new ecological niches.

- Animals such as fish and some invertebrate groups, such as eurypterids, were most common during this time invading freshwater habitats. Brachiopods were especially abundant during this time period.

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423 Million Years Ago
- It was during the Paleozoic Era that animals, known from Silurian fossils, at least 423 million years ago, began to colonize the land.

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419 Million Years Ago
- Often known as “The Age of the Fishes”. Lots of marine competition; animals began to invade the land (the first being arthropods).

- New species such as sharks, bony fishes, and ammonoids filled the oceans. Trilobites continue to decrease in population, while brachiopods still rose to the top towards abundancy.

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375 Million Years Ago
- The Late Devonian extinction consisted of several extinction events in the Late Devonian Epoch, which collectively represent one of five largest mass extinction events in the history of life on Earth.

- The causes of these extinctions are unclear. Leading hypotheses include changes in sea level and ocean anoxia, possibly triggered by global cooling or oceanic volcanism.

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360 Million Years Ago
- The Karoo ice age lasted around 100 million years between 360 to 260 million years ago. It is named after glacial tills in Karoo, South Africa that scientists think were developed during this ice age.

- It was the second major glacial period of the Phanerozoic eon.

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Carboniferous Period / Mississippian Period

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Carboniferous Period / Mississippian Period

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359 Million Years Ago
- The Mississippian Period is a subperiod in the geologic timescale of the geologic record. It is the earlier period of the Carboniferous period.

- Many insects evolved such as dragonflies & cockroaches. Dominated by arthropods. The amniotic egg evolved, which allowed for more successful reproduction among land animals.

- Bryozoans, brachiopods, and other marine life were most common during this time period.

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340 Million Years Ago
- The first amphibians appeared about 340 million years ago during the middle of the Mississipian Period.

- They were one of the earliest groups to diverge from ancestral fish-tetrapod stock during the evolution of animals from strictly aquatic forms to terrestrial types.

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Carboniferous Period / Pennsylvanian Period

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Carboniferous Period / Pennsylvanian Period

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323 Million Years Ago
- The Pennsylvanian Period is a subperiod in the geologic timescale of the geologic record. It is the later period of the Carboniferous period.

- Same as the Mississippian Period, many insects evolved, the period was dominated by arthropods, and the amniotic egg evolved allowing for more successful reproduction among land animals.

- Some animals that were common during this time period were corals, brachiopods, trilobites, snails along with other insects, squid-like animals, and microscopic animals

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300 Million Years Ago
- Reptiles originated approximately 300 million years ago during the Carboniferous period.

- One of the earliest undisputed reptile fossils was Hylonomus, a lizardlike animal about 20 centimeters long.

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299 Million Years Ago
- A great extinction occurred both on land and on sea. No one knows exactly what caused this extinction. It is estimated 95% of all the forms perished during the Permian Period.

- The Permian Period was a time of specialization for marine life, with major diversifications of ammonoids, brachiopods, and bryozoans. Insects, amphibians, and therapsids increased at this time.

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252 Million Years Ago
- Formed the boundary between the Permian and Triassic geologic periods, as well as between the Paleozoic and Mesozoic eras

- Warming of the Earth's climate and associated changes to oceans were the most likely causes of the extinction.

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251 Million Years Ago
- It was considered the mid-life and "The Age of the Reptiles”.

- This era contains three periods: Triassic, Jurassic, and Cretaceous.

-The ancestors of major plant and animal groups that exist today first appeared during the Mesozoic, but this era is best known as the time of the dinosaurs.

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251 Million Years Ago
- The Triassic Period is the first and shortest period of the Mesozoic Era.

- Organisms that survived the Permian extinction become prominent (many reptiles).

- The Coelophysis was the first known dinosaur, and the Lystrosaurus was the most common land vertebrate during the early Triassic period.

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230 Million Years Ago
- The prehistoric reptiles known as dinosaurs arose during the Middle to Late Triassic Period, about 230 million years ago.

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201 Million Years Ago
- It marks the boundary between the Triassic and Jurassic periods, 201.3 million years ago, and is one of the major extinction events of the Phanerozoic eon, profoundly affecting life on land and in the oceans.

- Huge and widespread volcanic eruptions triggered the end-Triassic extinction.

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201 Million Years Ago
- Dinosaurs ruled; birds began to evolve. Early mammals began to diversify. The sea life contained many familiar animals from today, such as sharks, rays, coral reefs and crocodiles.

- The Jurassic period was characterized by a warm, wet climate that gave rise to lush vegetation and abundant life. Many new dinosaurs emerged, among them were the stegosaurs, brachiosaurs, allosaurs, and many others.

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178 Million Years Ago
- Mammals first appeared at least 178 million years ago, and scampered amid the dinosaurs until the majority of those beasts, with the excepetion of birds, were wiped out 66 million years ago.

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145 Million Years Ago
- Many ferns and conifers ruled the land. and conifers  ruled the land. Flowering plants appeared during the Cretaceous. Many modern insects began to develop, such as ants and butterflies.

- The Cretaceous was a period with a relatively warm climate, resulting in high eustatic sea levels that created numerous shallow inland seas.

- Dinosaurs were the dominant group of land animals, especially “duck-billed” dinosaurs such as Shantungosaurus, and horned forms, such as Triceratops. Giant marine reptiles such as ichthyosaurs, mosasaurs, and plesiosaurs were common in waters, and flying reptiles dominated the sky.

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130 Million Years Ago
- They began changing the way the world looked as soon as they appeared on Earth about 130 million years ago, during the Cretaceous period.

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66 Million Years Ago
- It was considered the early life. Early on, the fossil record became rich with evidence of many types of highly diverse marine life.

- Rodents and small horses, such as Hyracotherium, are common and rhinoceroses and elephants appear. As the period ends, dogs, cats and pigs become commonplace.

- This era contains two periods: Tertiary and Quaternary

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66 Million Years Ago
- The Cretaceous–Paleogene extinction event was a sudden mass extinction of three-quarters of the plant and animal species on Earth.

- It was caused by the impact of a massive comet or asteroid 10 to 15 km wide which devastated the global environment.

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65 Million Years Ago
- Warm climate, grasses evolved- supported grazing animals. Dinosaurs gone; mammals able to reproduce more successfully (more space, briefly less predation). Birds also diversified and many of the birds we see today were present during the Tertiary.

- During the tertiary period, mammals diversified rapidly. Some examples were bears, hyenas, whales, dolphins, humans, and so much more.

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60 Million Years Ago
- Fossil records suggest that modern birds originated 60 million years ago, after the end of the Cretaceous period about 65 million years ago when dinosaurs died off.

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5-7 Million Years Ago
- The first human ancestors appeared between five million and seven million years ago, probably when some apelike creatures in Africa began to walk habitually on two legs.

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2.58 Million Years Ago
- This is the current period that we live in. Series of ice ages occurred. Earth’s climate began to warm about 20,000 years ago, glaciers melted, sea levels rose. Extinct animals of the quaternary included mastodons and saber-toothed cats.

- The Quaternary Period is famous for the many cycles of glacial growth and retreat, the extinction of many species of large mammals and birds, and the spread of humans.

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2.5 Million Years Ago
- The most recent ice age is the Quaternary ice age.

- We are currently in an interglacial stage of this ice age. It started around 2.5 million years ago and is still going.