BISC 102 Chapter Notes - Chapter 12, 13, 27, 28: Burgess Shale, Cambrian Explosion, Ctenophora
19 Jan 2018
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Today: oxygen = 21% of molecules in earth"s atmosphere. Researchers ----> no free molecular oxygen (o2) existed for first 2. 3 billion years of earth"s existence. No plausible source of oxygen at the time the planet was formed. The oldest earth rocks show that the first signs of oxygen appear many years after the formation of the planet. Even then, virtually all o2 reacted immediately with iron atoms to produce iron oxides, such as hematite (fe2o3) and magnetite (fe3o4). Cyanobacteria (photosynthetic) became numerous in oceans ~2. 7-2. 55 bya (fossil record). O2 common in oceans ----> cells use it as final electron acceptor during cellular respiration. More energy released as e- move through e- transport chains with o2. Almost all life forms unicellular for almost 3 by after origin of life. Show up in fossil record ~ 1 bya. ~565 bya, first animals (sponge, jellyfish and maybe simple worms) appear in fossil record. ~ 50 my later, every major group of animals appear.
