origin of earth Flashcards
eons
largest time division
Eons determined by
major changes in the Earth
Most recent Eon started with
started with the proliferation of multicellular animals = Phanerozoic Eon
what Three Eons make up what was previously know as the Precambrian Period
1) Proterozoic (most recent)
2) Archean
3) Hadean
hadean eon started
4.5 billion years ago
during the hadean eon
Earth & planets formed from dust and gasses surrounding the sun
Electromagnetic forces & Gravity gathers dust into large lumps, called planetisimals
collisions between lumps made lots of heat, made earth molten
Steam atmosphere formed
temperature of earth cooled and first rocks formed
Heavy elements in planets suggest
dust/gas from supernova
how do other solar systems form
They form in diffuse nebulae
planetisimals
Electromagnetic forces & Gravity gathers dust into large lumps
how did the steam atmosphere form from hadean eon
from light elements & water vapor from comet
oldest earth rock
3.8 billion years old
oldest meteorites and lunar rocks
4.5 billion years old
what destroyed all Earth rocks older than 3.8 by
erosion and plate tectonics
the Archean eon start and end
3.8 (oldest rocks) - 2.5 bya first life
Archean eon
Began with formation of solid rock
Volcanoes added heavier gasses to atmosphere (CO2, N2)
Water condensed
oceans formed
First life appeared on Earth (most primitive, most archaic)
Archean atmosphere
(CO2, H2O, N2- still in modern atmo)
(CO, H2S, HCl- rare in modern)
no free oxygen or ozone
oldest fossil
3.5 byo
life must have evolved before there was
free oxygen because oxygen breaks down macromolecules, and if they couldn’t form, neither could living cells
BIFS
banded iron formation
BIFS time line (start, peak, end)
began forming about 3.5 bya = 1st free O2
reached peak about 2.5 bya
deposition ended about 1.8 bya
early Archean sediment
dark colored, unoxidized, deposited before free oxygen
oxidized (rusted) sediment appears in the
Proterozoic Eon
what was Indirect (non-fossil) evidence for the presence of
Cyanobacteria – 3.5 bya
Banded iron formation
BIFS created
iron dissolves in anaerobic water
when iron bonds to O2 it becomes solid
the solid sinks to the ocean floor is deposited in layers
Layers of oxidized iron are red
what likely happened to form BIFS
O2 made by cyanobacteria at ocean surface
Toxic O2 removed by iron until iron runs out
Then O2 builds up & kills off most cyanobacteria
O2 levels drop
Unoxidized dark sediments deposited
Why are BIFs Banded?
When runoff added more Fe to the water the entire process stared over again. Iron has to move back in and cyanobacteria have to grow back
Proterozoic eon time
2.5-.54 billion years ago
what happened in Proterozoic
end of BIFS (consistent free oxygen)
Cyanobacteria resistant to oxygen poisoning by 1.8 billion years ago (early proterozoic)
Spontaneous formation of new cells no longer possible (because of free oxygen)
Diversification of bacteria
First Eukaryotes appear ( protists)
Ediacaran fauna appear (soft invertebrates)
Phanerozoic eon time
.54 bya- present
Phanerozoic eon
Began with the Cambrian explosion of multicellular animal species and complex land plants
