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The Early history of Earth!
After the Earth formed…about 4.6 Billion years ago…
…The Earth melted and differentiated into Core, Mantle, and Crust
The atmosphere… …lacked free Oxygen.
C
N
CC
C
CC
C
N
NN
NN
N
OO
O
(Oxygen is extremely reactive!!! It readily combines with almost everything!)
Time line
Hadean Eon
Formation of Earth
Archean Eon
Proterozoic Eon
PhanerozoicCenozoic
Mesozoic
Paleozoic
3.5BY
4.0BY
2.5BY
0.54BY
Algal Mats? Biochemistry?Maybe Yes
Life Starts?Continents formed
Life appeared more than 3.5 Billion years ago.
Early life forms did NOT use oxygen!
There was no free oxygen to use!
Some early life forms were poisoned by Oxygen…
The introduction of free oxygen may have killed off many early life forms.
O
O
O
O
The Atmosphere eventually became fairly similar to today’s, but still low on oxygen…
Early life forms were bacteria, and other single cell organisms like blue-green algae.
A common fossil from 1 to 3 Billion years ago is the STROMATOLITE…
Layers of algae and sediment that build up into easily recognizable mounds.
These are rare today…probably due to the evolution of the Snail!
As oxygen was added to the atmosphere, IRON deposition was altered. Vast Iron Ore deposits formed between 2 & 3 billion years ago…
Major deposition of this rock has not occurred since.
“Banded Iron” deposition ended as oxygen levels rose…
Time line
Hadean Eon
Formation of Earth
Archean Eon
Proterozoic Eon
PhanerozoicCenozoic
Mesozoic
Paleozoic
2.0BY
4.0BY
2.5BY
0.54BY
End of Iron Deposition
Cyanobacteria Iron Bacteria Stromatolites
Time line
Hadean Eon
Formation of Earth
Archean Eon
Proterozoic Eon
PhanerozoicCenozoic
Mesozoic
Paleozoic
1.5BY
4.0BY
2.5BY
0.54BY
Stromatolite Reefs
Time line
Hadean Eon
Formation of Earth
Archean Eon
Proterozoic Eon
PhanerozoicCenozoic
Mesozoic
Paleozoic
.85BY
4.0BY
2.5BY
0.54BY
…And then the bottom fell out!
Cryogenian Period
“Snowball Earth”?
Climate instability led to severe multiple ice episodes…
The worst of which MAY have frozen the entire surface of the planet!
Between 750 and 630 million years ago…
Or not…“Slushball Earth?
What’s the evidence for this?
Major changes in ocean pH…
Changes in C13\C12 ratio…
Due to increase in CO2?
Widespread biological losses?
Thick carbonate deposits… From extensive weathering after ice melt?
Banded Iron deposition… Oceans cut off from atmosphere by ice?
AND… Thick glacial deposits from this time.
The cold may have threatened life…or even may have been CAUSED by it.
Carbon dioxide from volcanic eruptions MAY have tipped the balance back to “normal” temperatures.
As the ice melted, temperature rose rapidly, and the stage was set for some major changes.
Most scientists now think that the Earth’s oceans did NOT entirely freeze over, but do agree that there was extensive glaciation at the time.
Time line
Hadean Eon
Formation of Earth
Archean Eon
Proterozoic Eon
PhanerozoicCenozoic
Mesozoic
Paleozoic
0.63BY
4.0BY
2.5BY
0.54BY
By 630 Million Years ago…
..the ice age had ended…
And by 630 million years ago, these major changes had begun…
This time is called the “Ediacaran Period”
Proterozoic
(Pre-Cambrian)
Ediacaran Period
Paleozoic Era
Mesozoic Era
Cenozoic Era
Oxygen levels had risen at the end of the ancient ice age…
542 MY
630 MYCryogenian Period
850 MY
… and the first indication of multi-celled organisms appeared in rocks about 600-610 million year old. Jellyfish, Anemones, and Sponges may date from about this time.
Recently (2014), probable fossil sponges were located in 700 million year-old rock.
The rocks of the Duoshantuo Formation are thought to be about 570-590 million years old. They contain fossils of…
Sponges…
Corals…
And possible animal eggs and embryos…
Grass-like Green Algae…
In rocks of ages between 575 and 555 million years ago, fossils of marvelous and complex animals are found…
Early Arthropods?
The EDIACARAN did NOT lack complex life forms!
But still a limited diversity of organisms.
Although more than 100 genera are known from the Ediacaran Period.
…And in the last few million years of the Ediacaran…
Shelly fossils appear…
This is the first indication of the NEXT major change!
The Ediacaran Period is just what we might expect to see…
…right after a time of small organisms of limited diversity…
Early Cambrian “critters” from the Burgess Shale.
..and just before a time of even more complex organisms of great diversity.