Geologic Time ES Chapter 11

Units of Geologic Time Earth is 4.6 billion years old Need to split up to make sense Periods are the basic unit Single rock system forms, often there is a mass extinction Era 2 or more periods Represent major changes in the fossil record End with a mass extinction Eon 2 or more eras

Geologic Timeline The eras and periods are not equal in length Defined based on events Periods are further divided into epochs Not discussing in this class…

Hadean Eon (Precambrian) 4.6 bya-4 bya Formation of earth to solidification of rocks No geologic record because no rocks Named after Hades “Hellish” Very hot A lot of volcanic eruptions Lava covering much of the surface A lot of collisions with space debris left over from planetary nebula

Formation of the moon (more to come later) Hadean Eon Likely due to collision between young earth and a large rocky object

Archean Eon (Precambrian) 4 bya-2.5bya Formation of the crust-first photosynthetic organisms Still very hot Atmosphere was mostly volcanic gases Little breathable oxygen, a lot of carbon dioxide Single-celled life formed near beginning and existed throughout

Proterozoic Eon (Precambrian) 2.5 bya-542 mya Oxygen becoming abundant-Cambrian explosion Geologic processes released oxygen Glaciation events Plate tectonics and supercontinent formation Evolution of eukaryotes and multicellular organisms Most had soft bodies Many existed for a short time, then went extinct

Evolution and Extinction in Geologic Record Evolution-Change in the traits in a population over time 1 species may split into 2 if they are reproductively separated Geographic isolation-populations of organisms becoming split due to geologic processes Tectonic plates provided a lot of geologic isolation Land bridges (a piece of land separating 2 previously isolated continents Evolution is driven by changing environments When conditions change, organisms can adapt, migrate, or they will die Extinction is the death of the last member of a species Mass extinctions occur when many species go extinct in a short geologic time (no more than a couple million years)

Phanerozoic Eon Current geologic eon (542mya-present) Life as we know it evolved (complex plants, fish, tetrapods, insects, dinosaurs, etc.) Formation and breaking-up of Pangea Eventual evolution of humans 3 eras distinguished by mass extinctions All end with “zoic” which comes from “zoe” meaning “life” 12 periods (11 in book. 1 has recently been split into 2)

Phanerozoic Eon-Paleozoic Era Longest era in Phanerozoic Eon 542 mya-251 mya Age of invertebrates 6 periods

Cambrian Period 542-468 mya Cambrian Explosion Still no life on land “Sudden” evolution of many complex organisms in water Happened over a period of about 100 million years Huge amount of diversity for the first time on Earth Some were similar to current life Cnidarians, mollusks, etc. Likely due to increase in oxygen levels (photosynthetic organisms), stabilization of temperatures, and decreased volcanism Still no life on land Earth was cool

Ordovician Period 488-444 mya A lot of invertebrates Began with Cambrian-Ordovician mass extinction Killed many trilobite species, along with others Ended with Ordovician-Silurian mass extinction Killed 50-60% of the species A lot of invertebrates Still no organisms on land Evolution continued, new species formed Mountain building and volcanic arcs Including Appalachian Mountains

Silurian Period 444-416 mya Earth warmed, glaciers melted Began with O-S mass extinction Ended with the aptly named End-Silurian mass extinction Earth warmed, glaciers melted Evolution of fish and terrestrial plants Also allowed some arthropods to leave the water

Devonian period 419-359 mya Age of the Fish Began with End-Silurian mass extinction Ended with Late Devonian mass extinction Mostly killed off trilobites Age of the Fish Included Tiktaalik, the ancestor to tetrapods (4-limbed organisms) A lot of organisms evolving on land Plants probably began causing land to green Soils beginning to form Coral reefs were common

Tiktaalik Video

Carboniferous Period 359-399 mya A lot of swampy forests Began at Late Devonian mass extinction Ended at the formation of Pangea A lot of swampy forests A lot of fossil fuels formed in this period Reptile evolved and became wide-spread Arthropods similar to those today, though much larger, evolved Dragonflys, 8-foot-long millipedes and centipedes (horrifying!)

Permian Period 299-251 mya Began at formation of Pangea Ended with a mass extinction that killed about 96% of all species Largest in Earth’s history, nearly wiped life out forever Ended the Paleozoic Era and the age of invertebrates Evolution of mammals, early alligators/crocodiles, turtles, and some large reptiles

Permian Period Video

The Mesozoic Era 251-65.5 mya The age of the dinosaurs 3 periods (most familiar to you) Triassic Period Jurassic Period Cretaceous Period

Triassic Period 251-200 mya Began with Permian mass extinction Ended with Triassic-Jurassic Extinction Wiped out many organisms and allowed dinosaurs to dominate Mammals and ancestors to birds and alligators dominated Pangea began to split apart Climate was mostly hot and dry No coal in the beginning as life was still recovering from Permian mass extinction

Triassic Period Video

Jurassic Period 200-145 mya Large herbivorous dinosaurs were common Began with Triassic-Jurassic mass extinction Ended with a minor mass extinction which killed most stegosaurid and sauropod dinosaurs Large herbivorous dinosaurs were common Some were already evolving into birds Not the dinosaurs you are most familiar with They came in the Cretaceous Period

Very minor Swearing

Cretaceous Period 145-65.5 mya Began with minor mass extinction Made way for most dinosaurs you are most familiar with Ended with Cretaceous-Paleogene mass extinction Asteroid that killed all non avian dinosaurs Plate movement led to North America beginning to form T. rex, velociraptors, triceratops, pterodactyls, and many other dinosaurs dominated Asteroid changed the climate and caused the extinction of 75% of organisms Made way for evolution of small mammals that survived

Crateous Period vid

Cenozoic Era 65.5 mya-current The age of mammals Began with the extinction of the dinosaurs The age of mammals Mostly small organisms survived the asteroid impact and climate change They quickly diversified to become more like modern organisms Earth became cooler, then stabilized Was divided into 2 periods (Tertiary and Quaternary), but recently was split into 3 Paleogene Neogene Quaternary

Paleogene Period 65.5-23 mya India and Asia were colliding Began with extinction of dinosaurs Ended ? India and Asia were colliding Most continents were nearing their current locations The first grasses evolved Savannahs and prairies formed Mammals were diversifying rapidly

Neogene Period 23-2.5 mya Began ? Ended with glaciation Mammals, including close ancestors of humans, continued to evolve North and South America connected, separating the Atlantic and Pacific Oceans Current Ice Age began Ice age-period of time when a large part of earth is covered in glaciers

Quaternary Period 2.5 mya-present Continents were nearly where they now are Mammoths, mastodons and saber-toothed cats went extinct Large period of glaciation All of the life around you evolved or already existed Humans evolved about 200,000 years ago in Africa and spread using land bridges