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 formed from volcanic gases…

Liquid Water condensed from Water Vapor… And the OCEANS formed…

The atmosphere… …lacked free Oxygen. C N C C C C C C N N N N N N OO O (Oxygen is extremely reactive!!! It readily combines with almost everything!)

Oxygen was bound into the rocks… …and into water. H-O-H 0-S

Time line Hadean Eon Formation of Earth Archean Eon Proterozoic Eon Phanerozoic Cenozoic Mesozoic Paleozoic 3.5BY 4.0BY 2.5BY 0.54BY Algal Mats?Biochemistry?MaybeYes 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!

New life forms evolved… some produced free oxygen! O O O O

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 Phanerozoic Cenozoic 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 Phanerozoic Cenozoic Mesozoic Paleozoic 1.5BY 4.0BY 2.5BY 0.54BY Stromatolite Reefs

Time line Hadean Eon Formation of Earth Archean Eon Proterozoic Eon Phanerozoic Cenozoic 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 Phanerozoic Cenozoic 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 MY Cryogenian Period 850 MY

… and the first indication of multi-celled organisms appeared in rocks about 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 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!

This was a time of… Small to relatively large organisms… And relatively complex organisms…

But still a limited diversity of organisms. Although more than 100 genera are known from the Ediacaran Period.

Tracks and trails become more common… …And more complex.

…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.

The Ediacaran Period: from about 630 to about 542 million years ago…

The Cambrian Period: from about 542 to about 488 million years ago…

Ediacaran Period Cambrian Period An “explosion” of diversity certainly… but NOT a sudden appearance of life! WHY??? A major shift in ocean pH may have allowed for life forms to evolve carbonate shells… Next: The PALEOZOIC!