The Geologic Column

Geologic Time Scale

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Largest = Eon (Hadean, Archeon, Proterozoic, Phanerozoic)

2nd Largest = Era (Paleozoic, Mesozoic, Cenozoic)

3rd Largest = Period (Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurrasic, Cretaceous, Tertiary, Quaternary)

4th Largest = Epoch (Mississippian, Pennsylvanian, Paleocene, Eocene, Oligocene, Miocene, Pliocene, Pleistocene, Holocene)

-Earth formed 4.6 billion years ago from a nebula around the newly formed sun.

-Makes up about 88% of Earth's history

-We know little about this time

-Lare areas of exposed precambrian rock called shields

-Result of several hundred million years of volcanic activity, mountain building, metamorphism, and sedimentation. 

-half of valuable deposits in the world are contained in shields

-fossils rare in precambrian rocks

-precambrian life lacked bones, shells, or other hard parts that commonly form fossils

-most common precambrian fossils are cynobacteria in stromalites.

-presence of stromalites means that much of earth was covered in a shallow ocean back then.

-Era began about 542 million years ago and ended 251 million years ago

-landmasses were once all seperated at first, came together at end of era

-abundance of fossils

-six periods

-First period of the paleozoic era

-life was more advanced than precambrian

-invertabrites thrived in the oceans, such as trilobites

-used trilobites as index fossils

-brachipods: shelled animals,

worms, jellyfish, snails, sponges

-trilobite numbers sunk

-brachiopods, bryozoans, cephalod mollusks became dominant

-fish appeared

-vertabrate and invertabrate life thrived

-more echinoderms and corals

-scorpian sea-like creatures called eurypterids

-fossils about 2m long have been found in western New York

-earliest vascular land plants and animals evolved on land

-called age of fishes because many bony fishes were discovered in fossils

-lungfish: could breathe air

-rhipidistians may have crawled on land

-early amphibians probably evolved from rhipidistians

-more plants, more mollusks

-climate was warm and humid

-much of world was forests and swamps

-amphibians and fish continue to flourish

-crinoids were common in the ocean

-towards end of the carboniferous period, vertabrates that adapted to life on land appeared

-early reptiles represented large lizards

-marks end of paleozoic era

-mass extinction because of tectonic movement

-trilobites and eurypterids went extinct

-lizards survived

-90% of marine and 70% of land organisms died

-evolved

-began 251 million years ago and ended 65 million years ago

-pangea brokeinto smaller continents (sierra nevada and andes are two examples)

-warm marshes

-the age of reptiles

-dinosaurs ruled the world

-some size of squirrels, others weighed as much as 15 tons (30,000 lbs, 13,608 kg)

-forests of cone-bearing trees and cycads (thick-stemmed plants with fern-like leaves)

-ichthyosaurs lived in oceans

-evolved marine life such as the ammonites

-first mammals

-official dinosaur time

-two groups

1. saurischians (lizard-hipped dinosaurs) included herbivores and carnivores, included the brontosaurus

2. ornithischians (bird-hipped dinosaurs) were herbivores, included the stegosaurus

-archaeopteryx was one of the first birds that appeared during the jurrasic period

-still dinosaurs

-one of the most spectacular is the tyrannosaurus rex

-6 meters tall, teeth were up to 15 cm long

-also armored ankylosaurs and duck-billed dinosaurs called hadrosaurs

-earliest flowering plants were angiosperms

-no dinosaur fossils found after mass extinction 65 million years ago

-caused by a meteorite crashing into the earth

-impact raised enough dust to block sunlight for several years

-earth became cooler

-plants died

-meteorite formed a layer of dust of iridium-laden sediment which is rare on earth but common on asteroids

-began 65 million years ago and still is going along

-continents moved to present-day locations

-huge mountain rages such as the alps and himalayas were formed

-dramatic changes in temperature often 

-age of mammals

-tertiary was time before the last ice age

-quaterney begins with the last ice age until now

-paleocene, eocene, oligocene, miocene, pilocenem epochs make tertiary period

-pleistocene and holocene epochs make up the quaterney period

-many mammals (small rodents) evolved

-primates and earliest known ancestor of the horse also evolved

-first whales, flying squirrels, and bats appeared

-small reptiles were okay

-temperatures dropped about 4°C at end of eocene epoch

-during oligocene, indian subcontinent began to collide with eurasian continent (himalayas formed)

-early mammals became extinct

-large species of deer, pigs, cats, and dogs flourished

-circumpolar currents began to form (antarctic ice was starting to form)

-miocene has horses, camels, deep, rhinos, pigs, raccoons, wolves, foxes, saber-toothed cats, possibly the earliest human ancestors

-predators evolved into modern form

-herbivores flourished

-towards end, dramatic climate changes

-ice age

-bering land bridge, central american land bridge

-began 1.8 million years ago

-ice sheets advanced and retreated several times in the northern hemisphere

-wooly mammoths got fur

-some species like giant sloths and dire wolves became extinct

-early humans were most likely hunters

-began 11,500 years ago

-last glacial period ended

-seas rose 140 meters at beginning of epoch

-coastlines took present shapes

-humans developed tools made of bronze and iron, agriculture

-human history is extremely brief (if earth had a whole year in its existence, humans wouldn't appear until 11:48 p.m. on December 31st)