a biography of the earth Flashcards
geologic time scale
Epochs
Smallest time blocks
Periods
Made of many epochs
Eras
Made of many periods
Eons
Made of many eras
Largest time blocks
Precambrian eons: hadean
youngest to oldest:
Proterozoic
Archean
Hadean birth-4.0Ga(billion yrs.) oldest
Intense meteorite bombardment
Volcanoes: Outgassing creates secondary atmosphere
N2, NH3, CH4, H2O, CO, CO2, & SO2 (the earth has no primary atmosphere, we’re not big enough)
Liquid water collects into early oceans
no life!
precambrian eons; archean
Archean 4.0-2.5 million yrs ago
Cooling Earth
Continental crust creation
Plate tectonics!
Life first appears
~3.5 Ga
Chemical evidence of life (see things that are from biologic processes)
Could be as old as 3.8 Ga
~3.2 Ga
Bacterial cell fossils
Blue-green algae
Stromatolites
Pumps free oxygen into the atmosphere
free oxygen is highly flammable
stomatilites
evidence in fossilled layer and current microbial mats
precamrbian eons: proterozoic
Proterozoic 2.5-.5 billion years ago
“First Life” (named before Archean life was discovered)
2 billion years
Oxygenated atmosphere
90% continental crust present by middle Proterozoic
Proterozoic oxygen
Tertiary Atmosphere
Created by LIFE
Rapid rise of free oxygen
Evidence:
Banded Iron Formations
Major source of iron ore today
Reddish when deposited
Indicates free oxygen atmosphere
proterozoic north america
United States
Precambrian rocks are covered by sedimentary rocks of the stable platform
Canadian Shield
Precambrian rocks are visible at the surface
Archean interior
Proterozoic arcs and crustal slivers were added through plate tectonics (convergence)
supercontinents cycle
Continents periodically collide
May create a “supercontinent”
Continents eventually rift apart
Heat is trapped under the massive supercontinent
Thins and rifts the interior, initiating divergence
Rodinia (snowball earth time)
~1 Ga - ~700 Ma
Gondawana
~550 Ma – 100 Ma
Pangea
300 Ma – 200 Ma
gondwana
Not Gondwanaland
Gondwana means “Land of the Gonds”
“Gonds”
Derived from a tribe in India
see screen shot of tan land on blue ocean
Proterozoic life
1.0 Ga
Eukaryotic (nucleated) cells
1.0 Ga – 500 Ma
Biological complexity
Ediacaran fauna
Multicellular invertebrates
(Worm- and jellyfish-like)
Phanerozoic
Eras
Cenozoic
Mesozoic
Paleozoic
Most recent 541 Ma of Earth history
Hard-shelled organisms debut
(Much nicer for fossilization)
early Paleozoic era
Transgressions
Cambrian-Ordovician
Flooded the low-lying interior of North American
Orogenies
First of several Appalachian orogenies begins in the Ordovician
Cambrian Explosion
Marine life thrived in the warm, shallow oceans of the transgressions
Rapid evolutionary diversification
early paleozoic life
Cambrian Explosion
Marine life thrived in the warm, shallow oceans of the transgressions
Rapid evolutionary diversification
Ordovician diversity
First vertebrates
Crinoids
Primitive land plants
mass extinction at the end of ordovician
85% of all species gone
Causes:
Sea level drop (regression) & global cooling
Sea level rise & global warming
middle Paleozoic era
Silurian and Devonian
Greenhouse warming
Hot!
Transgressions
Orogenies
Second of several Appalachian orogenies begins in the Devonian
middle paleozoic life
Rich marine diversity
First animals to walk on land
Amphibians
Walking on legs, breathing with lungs
Tiktaalik (late Devonian)
Lobe-finned fish fossil
Discovered in 1996
Transitional between fish and amphibians
