Geologic HistoryVery Brief Version

charity mulig

Geologic Time Scale

Precambrian

Lithosphere

Early Very hot, no permanent crust.

Middle Land cooled to temperature lower than the boiling point of water.

Late Formation of iron ores (hematite) which are usually found underwater (am indication that life is concentrated in the seas)

Atmosphere

Early No atmosphere. Air similar to gases released by volcanoes.

Middle No free oxygen. Reduced amount of vapor and CO2 in the atmosphere.

Late All free Fe have combined with 02. hence an increase in atmospheric O2.

Hydrosphere

Early No water on land.

Middle Formation of lakes and seas on low-lying areas.

Late Increased dissolved O2. Presence of aerobic organisms.

Biosphere

Early No life.

Middle Anaerobic life confined in the seas. Mostly algae and unicellular bacteria and other prokaryotes.

Late Presence of eukaryotes and photosynthetic plants.

Fossils

• Stromatolites and other trace fossils•Microfossils found in chert.

Rocks

Shields are deformed metamorphic rocks found at the heart of continents.

Paleozoic

Lithosphere

Early Gondwanaland in the south while Laurasia is yet unformed.Early N. America is barren lowland covered by shallow seas follwoed by mountain building and another period of inundation of shallow seas resulting to formation of evaporites

Late Collision of N. America and Africa (formation of Appalachian Mt)Convergence of other continents (W. Asia + Siberia = Ural Mt)Laurasia + Gonwanaland = Pangaea (lead to increase in elevation)

Atmosphere Late Drier climate.Hydrosphere Variable.

Biosphere Early Appearance of animals with hard part s(shells, exoskeletons, cartilage) and cephalopods (1st truly large animals).

Late Life diversified. Appearance of 1st terrestrial plants, insects , fishes , and swamps which became coal mines.

Fossils Trilobites, brachiopods.Lobe-finned fish and lung fish.

Mesozoic

Lithosphere

Early Most lands above sea level. Middl

eN. America covered by shallow seas (evidenced by continental sediment deposits). Much of SW America is desert.

Late N. America covered by swamps forming coal deposits.Start of break up of Pangaea. N America (formation of mountains in W America and intrusion in Midwest America). Formation of Rocky mountains.

Biosphere Survivors of Paleozoic extinctions diversified. Development of gymnosperms. Perfection of the reptilian egg. Domination of dinosaurs (adaptive radiation)

Fossils Example of gymnosperms (cycads, gingkoes, conifers) are found in Arizona’s Petrified forest National Park.Sarchosuchus imperator

Rocks Presence of iridium in the KT boundary suggest a meteoritic collision.Lava plateau suggests a volcanic eruption.

Cenozoic

Lithosphere Early E. America. Passive margin. Massive deposits caused down warpind and faulting. Faults created traps of oil and natural gas. Appalachians eroded.End of Rocky mt formation led to deposition in the great plains.Creation of Basin and Range province I Nevada and Mexico by crustal uplifting.

Late Raising of Applachians by isostatic movements lead to deposition in Atlantic and Gulf Coast plains.Uplifting of Rockies and formation of Grand Canyon and other gorges.Volcanic Activity lead to the cascade range and the formation of columbia plateau.

Biosphere Survivors of the KT extinction.Mammals replaced reptiles as dominant land animals.Angiosperm replaced gymnosperm as dominant plants. Rapid diversification of plants and birds.Development of grass, grazing animals and predators.

Fossils Foraminifera.Extinction of large mammals attributed to selective hunting by humans.

Rocks Folding and glaciations gave finishing touches.