Nebular Hypothesis
Formed from a primordial cloud: 5 bya contraction of rocky fragments after the big bang; rocks and gases rotate and flatten into a disk; planets begin to coalesce; largest mass is the sun; proto-sun formed by gravitational heating; cooling of rotating dis
Today's air components:
79% nitrogen; 20% oxygen; 1% argon; traces of carbon dioxide & water vapor
Out-gassing from volcanoes
Water vapor, carbon dioxide, nitrogen, trace gasses; origin of waetr vapor came fom volcanoes
When did crust begin to form and why?
4.4 bya; cooling of crust accelerated by formation of clouds (water vapor)
Where did oxygen come from?
3.8 bya; green algae plants
-photosynthesis
Photosynthesis
CO2 + H2O --> Sunlight --> Glucose Sugar + Oxygen
-plants use light to combine carbon dioxide and water into sugars and oxygen
Red Beds
Oxygen combines with iron worldwide; all iron-ore deposits in shallow lakes and seas
Animals appear
570-540 mya; bginning of Paleozoic
Precambrian Rocks
Precambrian shields (low-lying "cores" of continents; iron-ore deposits/ Red Beds; 4.5-4.6 bya
Precambrian Fossils
-Bacteria & blue-green algae preserved in chert (3.4-3.6 bya)
-Stromatolites algae mats (2 bya)
-Eukaryotes (1.0 bya)
-worm tubes (tracks and trails of soft-bodied animals)
Cambrian
Age of trilobites (crab-like creatures)
Ordovician
Brachiopods, cephalopods (squid) appear; clams (bivalves), sponges, corals, first platy fish
Early Paleozoic
Includes Cambrian, Ordovician, Silurian periods
Devonian
land of plants; age of fishes (first show up in Silurian, then dominate in Devonian); fish adapt to land * first amphibians
Pennsylvanian
age of swamps and forests; coal deposits form
Mass Extinction
end of Permian Period; 75% amphibians & all trilobites GONE); 251 mya
Mesozoic Age
age of dinosaurs: Triassic, Jurassic, Cretaceous
Break-up of Pangaea
formation of Atlantic Ocean; continents form
Triassic
red Beds"; much of world's land above sea level; 248 mya
Jurassic
shallow seas
Cretaceous
shallow seas, great swamps, reptiles at their peak; formation of western US and Canadian coal deposits
Mesozoic Life
-seed-bearing plants: cycads, confiers, ginkgoes
-shelled eggs of reptiles can be laid on land
-dinosaurs dominate
-KT Extinction
KT Extinction
- (Cretaceous Tertiary extinction) end of dinosaurs
Possible causes:
-10k meteorite collided near Yucatan Mexico (*iridium layer around the world)
Cenozoic Era
age of mammals; Tertiary and Quaternary periods
Cenozoic North America landscape
Eastern N. America: eroded to broad flatlands; up-warping of Appalachian "Mountains"
Western N. America: convergent plate margin forms: Rocky Mountains; California, Nevada, Utah basin and range
Cenozoic Life
mammals, flowering plants (1.6-1.8 mya)
-marsupials & placentals; mammal diversity until Late PLiocene land bridge
-large mammals- Oligocene; world-wide extinction by late Pleistocene (ended 11kya/today's time period)