Geologic Time Project

Alyssa McCandlish and Rachel Grief

Part Two ~ Precambrian Time

~ Atmosphere ~

What did the early atmosphere look like? The atmosphere during the precambrian time period is not well understood but it is believed to have been composed of mainly carbon dioxide and nitrogen. Scientists believed it did not provide a well and steady source of oxygen.

~ Major Events ~

What did earth first look like? In the beginning the earth was simply a large and very hot ball that evaporated every bit of water into the atmosphere. As the earth cooled, the water in the atmosphere fell as rain.

When did the oceans form? During the first rain, the immense amount of water that fell from the atmosphere became trapped in what are now oceans and lakes.

When did the moon form? During the earth's formation, a large almost mars-sized planet struck the earth and blasted debris out into space. From there, the debris collected together due to gravitational pull. This theory is supported by the age of the rocks on the earth and the moon.

How old is the earth? The earth is believed to have formed about 4.6 billion years ago.

When did the continents form? During the Proterozoic Eon there were hundred of small land pieces floating around. These plate eventually collided due to plate tectonics. By 2.5 billion years ago, about one-fourth of the earth's crust was formed. It is thought that Pangaea began forming about 300 billion years ago.

What organisms were in each eon?

Hadean ~

The Hadean Era is the second earliest era (right after the Caotian Era). During this era there isn't any evidence of living organisms. Continents continued to form and the Archean crust was developed towards the end of this time span.

Archean ~ During this time period, the crust and continents continued to form. It is possible that the first stromatolites appeared. Also this era is the first for fossil evidence of life to be widely accepted. Also during the Archean era, the first large continental shields were formed.

Proterozoic ~ The proterozoic era contains over half of life's history on earth. There is little evidence to prove it though. The most discovered organisms during this period are the acritarchs. Nobody knows exactly what they are or where they came from, but they are very abundant. Also the most successful group of this period in time were the sponges.

~ Citations ~

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