Monday, December 10, 2007

Concept 26.3

Q1: What do fossilized stromatolites suggest about the evolution of prokaryotes?

A1: Prokaryotes must have existed at least 3.5 b.y.a, when the oldest fossilized stromatolites were formed.

Q2: The first appearance of free oxygen in the atmosphere must have triggered a massive wave of extinctions among the prokaryotes of the time. Why?

A2: Free oxygen attacks chemical bonds and can inhibit enzymes and damage cells. Some organisms were able to survive in anaerobic habitats, however.

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