Evolution Over Time

Paleozoic Era 540 to 248 mya

Hadean Eon
4.6 to 3.9 billion years ago

The Hadean is the first geologic eon of Earth and lies before the Archean. It began with the formation of the Earth about 4540 million years ago and ended as defined by the Ics 4,000 million years ago. The name "Hadean" comes from Hades, the ancient Greek god of the underworld, in reference to the "hellish" conditions on Earth at the time: the planet had just formed and was still very hot due to high volcanism, a partially molten surface and frequent collisions with other Solar System bodies.

Archeozoic Eon

3.9 to 2.5 billion years ago

("Ancient Life" The first life forms evolve one celled organisms. Blue-green algae, archeans, and bacteria appear in the sea. This begins to free oxygen into the atmosphere.)

Scientific evidence suggests that life began on Earth at least 3.5 billion years ago. The earliest evidences for life on earth are graphite found to be biogenic in 3.7 billion-year-old metasedimentary rocks discovered in Western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia.

Fossils of cyanobacterial mats (stromatolites, which were instrumental in creating the free oxygen in the atmosphere) are found throughout the Archean, becoming especially common late in the eon, while a few probable bacterial fossils are known from chert beds. In addition to the domain Bacteria (once known as Eubacteria), microfossils of the domain Archea have also been identified.

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Proterozoic Eon
2.5 billion years ago to

(First multicellular life: colonial algae and soft-bodied invertebrates appear. Oxygen build-up in Mid-Proterozoic.)

Many of the most exciting events in the history of the Earth and of life occurred during the Proterozoic — stable continents first appeared and began to accrete, a long process taking about a billion years. Also coming from this time are the first abundant fossils of living organisms, mostly bacteria and archaeans, but by about 1.8 billion years ago eukaryotic cells appear as fossils too.

Phanerozoic Eon
"Visible Life"
Organisms with skeletons or hard shells.
540 mya through today.

Cambrian Period
"The Age of Trilobites"
540 to 500 mya

"Age of Trilobites" -The Cambrian Explosion of life occurs; all existent phyla develop. Many marine invertebrates (marine animals with mineralized shells: shell-fish, echinoderms, trilobites, brachiopods, mollusks, primitive graptolites). First vertebrates. Earliest primitive fish. Mild climate. The supercontinent Rodinia began to break into smaller continents (no correspondence to modern-day land masses). Mass extinction of trilobites and nautiloids at end of Cambrian (50% of all animal families went extinct), probably due to glaciation.

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Ordovician Period
505 to 438 mya

Primitive plants appear on land. First corals. Primitive fishes, seaweed and fungi. Graptolites, bryozoans, gastropods, bivalves, and echinoids. High sea levels at first, global cooling and glaciation, and much volcanism. North America under shallow seas. Ends in huge extinction, due to glaciation.

Silurian Period
438 to 408 mya

The first jawed fishes and uniramians (like insects, centipedes and millipedes) appeared during the Silurian (over 400 million years ago). First vascular plants (plants with water-conducting tissue as compared with non-vascular plants like mosses) appear on land (Cooksonia is the first known). High seas worldwide. Brachiopods,crinoids, corals.

Devonian Period
"The Age of Fishes"
408 to 360 mya

Fish and land plants become abundant and diverse. First tetrapods appear toward the end of the period. First amphibians appear. First sharks, bony fish, and ammonoids. Many coral reefs, brachiopods, crinoids. New insects, like springtails, appeared. Mass extinction (345 mya) wiped out 30% of all animal families) probably due to glaciation or meteorite impact.

Wide-spread coal swamps, foraminiferans, corals, bryozoans, brachiopods, blastoids, seed ferns, lycopsids, and other plants. Amphibians become more common.
360 to 280 mya

Mississippian Period
360 to 325 mya

First winged insects.

Pennsylvanian Period
325 to 280 mya

First reptiles. Many ferns. The first mayflies and cockroaches appear.

Mesozoic Era

"The Age of Reptiles"
248 to 65 mya

Triassic Period
248 to 208 mya

The first dinosaurs, mammals, and crocodyloformes appear. Mollusks are the dominant invertebrate. Many reptiles, for example, turtles, icythyosaurs. True flies appear. Triassic period ends with a minor extinction 213 mya (35% of all animal families die out, including labyrinthodont amphibians, conodonts, and all marine reptiles except ichthyosaurs). This allowed the dinosaurs to expand into many niches.

Jurassic Period
208 to 146 mya

Many dinosaurs, including the giant Sauropods. The first birds appear (Archaeopteryx). The first flowering plants evolve. Many ferns, cycads, gingkos, rushes, conifers,ammonites, and pterosaurs. Minor extinctions at 190 and 160 mya.

Cretaceous Period
146 to 65 mya

(Lower 146-98 mya)

The heyday of the dinosaurs. The first crocodilians, and feathered dinosaurs appear. The earliest-known butterflies appear (about 130 million years ago) as well as the earliest-known snakes, ants, and bees. Minor extinctions at 144 and 120 mya.

(Upper 98-65 mya)

High tectonic and volcanic activity. Primitive marsupials develop. Continents have a modern-day look. Minor extinction 82 mya. Ended with large extinction (the K-T extinction) of dinosaurs, pterosaurs, ammonites, about 50 percent of marine invertebrate species, etc., probably caused by asteroid impact or volcanism.

Cenozoic Era

"The Age of Mammals"
65 mya through today

Tertiary Period

65 to 1.8 mya

65-24 mya

65-54 mya

First large mammals and primitive primates, plesiadapiforms.

54-38 mya

Mammals abound. Rodents appear. Primitive whales appear.

38-24 mya

Starts with a minor extinction (36 mya). Many new mammals (pigs, deer, cats, rhinos, tapirs appear). Grasses common.

24-1.8 mya


24-5 mya

More mammals, including the horses, dogs and bears. Modern birds. South American monkeys, apes in southern Europe, Ramapithecus.

5-1.8 mya

First hominids (australopithecines). Modern forms of whales. Megalodon swam the seas

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Quaternary Period
"The Age of Man"
1.8 mya to today

The Last Ice Age
1.8-.011 mya

The first humans (Homo sapiens) evolve. Mammoths, mastodons, saber-toothed cats, giant ground sloths, and other Pleistocene megafauna. A mass extinction of large mammals and many birds happened about 10,000 years ago, probably caused by the end of the last ice age.


11,000 ya to today

Human civilization

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