Timeline of Life on Earth

The Hadean: 4,600 – 4,000 million years ago Pre-Cambrian The Hadean: 4,600 – 4,000 million years ago Not technically a geological era No rocks from this time have survived

The Archean: 4,000 – 2,500 million years ago Pre-Cambrian The Archean: 4,000 – 2,500 million years ago Era begins with the oldest rocks (4 bya) First life appears in the fossil record at 3.8 bya Life was purely bacterial for 1000 million years Bacterial lived in mounded colonies called stromolites living stromatolites persist today in western Australia

The Proterozoic: 2,500 – 542 million years ago Pre-Cambrian The Proterozoic: 2,500 – 542 million years ago Stromolite presence in the fossil record grows, along with species diversity First pollution crisis in the fossil record at 2.2 bya. Rocks start showing metal oxides -> points to oxiiication of atmosphere Cyanobacteria responsible for “poisoning” the air, stromatolite abundance declines at 700 mya Eucaryotes first appear in the fossil record at 1800 mya First animals appear in fossil records at 635 mya cyanobacteria

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The Cambrian: 542 – 485.4 million years ago Phanerozoic: Paleozoic The Cambrian: 542 – 485.4 million years ago Explosion of extant phyla, except Bryozoa While the phyla are extant, Cambrian animals belong to classes not found in the present brachiopods were exceptionally common and diverse everything still living in the seas brachiopod

The Ordovician: 485.4 – 443.8 million years ago Phanerozoic: Paleozoic The Ordovician: 485.4 – 443.8 million years ago Begins with the Cambrian–Ordovician extinction event: extinction of brachiopods and trilobites (not considered a mass extinction) Ordovician is known for establishing ecological diversity in the seas: reef- forming corals, filter feeders, etc. Mollusks diversified, first jawed fish appears in fossil record nautiloids

The Silurian: 443.8 – 419.2 million years ago Phanerozoic: Paleozoic The Silurian: 443.8 – 419.2 million years ago Begins with the first mass extinction: Ordovician–Silurian mass extinction Second-largest mass extinction (actually two pulses): 60% of the marine invertebrate fauna went extinct Major diversification of jawed and boney fish first land vascular plants (mosses), but not very important Also very first land animal: a millipede (428 mya) Silurian fish

The Devonian: 419.2 – 358.9 million years ago Phanerozoic: Paleozoic The Devonian: 419.2 – 358.9 million years ago Begins with adaptive radiation of terrestrial life Free-sporing plants colonized dry land, leaving massive forests Terrestrial arthropods diversified: only possible because of dominance and diversification of land plants Age of fish: first ray-finned fish appear (Actinopterygii, 99% of extant fish species belong to this class) Ends with the second mass extinction: actually two events. Several competing theories. Devonian

The Carboniferous: 358.9 – 298.9 million years ago Phanerozoic: Paleozoic The Carboniferous: 358.9 – 298.9 million years ago Massive forests (ferns, horse-tails, and other non- flowering plants) Coal deposits formed because of un-decomposed woody material (first trees) in massive swamps, (and probably because bacteria and fungi hadn’t yet evolved to efficient enzymes for decomposition). Age of the terrestrial amphibian. Some 6 meters long! Amniotic egg develops (allows for radiation of terrestrial tetrapods: turtles, reptiles, birds, mammals) Carboniferous forests turtle egg

The Permian: 298.9 – 252.17 million years ago Phanerozoic: Paleozoic The Permian: 298.9 – 252.17 million years ago Begins with the Carboniferous rainforest collapse, where swampy forest gave way to arid deserts Pangea is formed At beginning of Permian, 90% of insects were cockroach- like Blattoptera. Giant dragonflies evolve. Late Permian: many other species rich insect orders are formed: Hymenoptera (bees, wasps), Coleoptera (beetles), Lepidoptera (butterflies), Diptera (flies). Most significant time for insect radiation. Drier conditions favored amniotes: first fossils of mammals, turtles, lepidosaurs (modern reptiles), and archosaurs (dinosaurs, crocodiles, birds). Permian

The Permian – Triassic mass extinction: 252.17 million years ago 80% of marine genera go extinct Estimated that 96% of marine species, 86% of insect genera, and 70% of terrestrial vertebrates went extinct Took between 10 and 30 million years for biodiversity to recover Causes unclear: bolide impact, volcanism, methane gasification (maybe because of sea level drop or new enzymatic pathway in microbes, sudden increase in CO2 causing ocean die off and cascade… massive ecological rearrangement favors pioneer taxa, in plants, particularly lycophytes (club mosses)

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The Triassic: 252.17 – 201.3 million years ago Phanerozoic: Mesozoic Low diversity persists for long time during Triassic Dominant marine habitats shifts from sessile to benthic Pangea begins to split into Laurasia and Gondwana in mid-Triassic Land plants dominated by confiers, cycads, ginkgos, and ferns It takes a long time for dinosaurs to become dominant: late Triassic opens the “Age of Dinosaurs” Lystrosaurus: most dominant land vertebrate of early Triassic

The Jurassic: 201.3 – 145 million years ago Phanerozoic: Mesozoic Once again, begins with a mass extinction event: the Triassic–Jurassic extinction event: 1 of 2 species goes extinct in just 10,000 years! On land, ecological niches open to allow dinosaurs to dominate. (Volcanoes are best guess as to cause) There were still no flowering plants – all trees were conifers! Sauropods: large, herbaceous dinosaurs dominate

The Cretaceous : 145 – 65 million years ago Phanerozoic: Mesozoic Flowering plants appear (but not dominant) Mammals and birds also are more apparent (technically, both groups first appear in Jurassic) Era of the best known dinosaurs: T. rex, Triceratops, Velociraptor, etc. Abruptly ends with the K-T mass extinction. 75% of plant and animal species go extinct, including all non-avian dinosaurs Triggered by massive comet/asteroid impact in Yucatán Reconstruction of type specimen (CM 9380) of Tyrannosaurus rex (Carnegie Museum of Natural History)

The Paleocene : 66 – 38 million years ago Phanerozoic: Cenozoic Nearly every bird order radiated during first 10 million years. Mammals radiate afterwards Starts hot and humid, ends cooler and drier. Tropical forests found in Alaska. Fifth mass extinction occurs during this period: mostly marine, maybe not really a mass extinction

The Neogene : 38 – 2.58 million years ago Phanerozoic: Cenozoic Seasonality dominates climate (before, climate wasn’t very seasonal!) Global climate continues to cool. Deciduous forests and grasslands replace tropical forests Isthmus of Panama forms at 3 mya, creating the jet stream

The Quaternary : 2.58 million years ago to present Phanerozoic: Cenozoic Ice Ages! It is generally believed that Quaternary climate patterns shape the current distribution of most terrestrial plants and animals. A genus of stone-tool using apes first appears in the fossil record