The Geologic Time Scale

The Geologic Time Scale - The Geologic Time Scale These...

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The Geologic Time Scale These ancient fossils occur in marine rocks, such as limestones and sandstones, that formed in ancient oceans. The organisms living today that are most similar to ancient life forms are the archaebacteria (the archaea in modern usage). This group is today restricted to marginal environments. Recent discoveries of bacteria at mid-ocean ridges add yet another possible origin for life: at these mid-ocean ridges where heat and molten rock rise to the earth's surface. Many of the ancient phototrophs and heterotrophic bacteria lived in colonial associations known as stromatolites. Cyanobacteria are on the outer surface, with other photosynjthetic bacteria (anoxic) below them. Below these phottrophs are layers of heterotrophic bacteria. The layers in the stromatolites are alternating biogenic and sedimentologic in origin. The Proterozoic Eon covers the time span from 2.5 billion to 544 million years ago. Simple, prokaryotic cells still dominated the world's environments until the evolution of simple
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This note was uploaded on 11/29/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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The Geologic Time Scale - The Geologic Time Scale These...

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