BIO 111 Chapter Notes - Chapter 18, 41: Cambrian Explosion, Ordovician, Devonian

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3 Mar 2017
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18. 3 major events in the evolution of life can be read in the fossil record (5 pages) To reconstruct the physical changes in the environment and their effects on life, researchers use fossil record. Precambrian life was small and aquatic: at first, life was mostly small and aquatic for a several possible reasons. Not enough oxygen in the atmosphere to support for the larger organisms. Extreme cold weather (the snowball hypothesis) claims that life was confined to warm places such as hot springs, deep thermal vents, and a few equatorial oceans. These areas would not have been able to support larger life. Many groups of organisms that arose during the cambrian later diversified: the ordovician first period of the remainder of the paleozoic era. Most of the continents were in the southern hemispheres. At the end, sea levels dropped significantly causing 75% of the animals to become extinct: the silurian. Marine life returned after the disaster of the ordovician.

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