Eons and Eras

Hadean Eon

4.6-4.0 Ga, earth was formed

Archean Eon

4.0-2.5 Ga, earth cooled and was able to support oceans, tectonic activity built continents, oxygen-filled the oceans from cyanobacteria and formed banded iron formations, most of the world’s iron ore deposits were produced in this eon from banded iron formation

Proterozoic eon

2.5-.5 Ga, cyanobacteria threatened their own existence through their own waste oxygen, earth froze over, oxygen atoms could bond to form clouds and the ozone thickened, eukaryotes emerged

Paleozoic era

520-252 Ma, the first apperance of animal life in fossil records, the cambrian explosion occurred, largest diversification of life in earths history, ended with the largest extinction in earths history, invertebrates, fish and amphibians evolved, reptiles and dinosaurs become the dominant life

cambrian period

oxygen levels were approaching modern levels, cambrian explosion, major groups of animals living today appeared

ordovician period

488-444 Ma, radiation of marine organisms occurred, brachiopods and mollusks, end of period: glaciers formed and dropped sea levels so a mass extinction occurred

silurian period

444-416 Ma, marine life rebounded, first vascular plants appeared and terrestrial arthropods (scorpions and millipedes)

devonian period

416-359 Ma, evolutionary radiations of corals and quid-like cephalopods, jawed fishes replaced jawless forms, club mosses, horsetails, and tree ferns became common + some tree size, first soils developed, first seed plants, first fossils of centipedes, spiders, and insects and the first terrestrial vertebrates, mass extinction resulted in loss of 75% of marine species (maybe meteorites)

carboniferous period

359-299 Ma, large glaciers formed over high altitudes, swamp forests of horsetails and tree ferns grew on the tropical continents, diversity of terrestrial animals increased (snails, centipedes, scorpions, and insects), insects evolved large wings, amphibians became larger and a sister lineage led to amniotes

permian period

299-251 Ma, continents merged to form supercontinent pangaea, end of the period: amniotes split into reptiles and mammals, ray-finned fishes became common in fresh waters, massive volcanic eruptions poured lava and ashes and gases blocked sunlight resulting in biggest glaciers in earths history, extinction led to loss of 96% of all species

mesozoic era

252-66 Ma, age of dinosaurs, pangaea starts to rift apart, age of conifers begins, mammals and flowering plants appear

triassic period

251-206 Ma, on land conifers and seed plants become dominant, a great radiation of reptiles began which gave rise to crocodilians, dinosaurs, and birds, mass extinction at the end eliminated 65% of species

jurassic period

199-245 ma, ray-finned fishes diversified rapidly, first lizards and flying reptiles appeared, most large terrestrial animals were dinosaurs, mammals and flowering plants appeared, pangaea divided into laurasia (north0 and gondwana (south)

cretaceous period

145-66 ma, modern continents began to form, continuous sea encircled the tropics, earth was warm and humid, snakes appeared, flowering plants began their dominance, many mammal groups evolved, mass extinction caused by a meteorite, animals larger than 25kg became extinct, insects became extinct

cenozoic era

66 ma-now, positions of continents resemble today, radiation of mammals, flowering plants dominated forests, cool regions- gymnosperms dominated