BISC 121Lg Lecture Notes - Lecture 19: Louis Pasteur, Cellular Respiration, Cyanobacteria
Document Summary
Life originated 3. 5 to 4 billion years ago from leftovers of the old solar system. For the first of life"s history, all orga(cid:374)is(cid:373)s were (cid:373)i(cid:272)ros(cid:272)opi(cid:272) a(cid:374)d (cid:373)ost were u(cid:374)i(cid:272)ellular. Earth was very hot and bombarded with meteors, making life impossible. Oldest rocks are about 3. 8 billion years old. Oldest fossils are about 3. 5 billion years old from western australia: resemble bacteria, earth may have had life around 3. 9 billion years ago. Prokaryotes dominated life from 3. 5 to 2 billion years ago: stromatolites and sediments from hydrothermal vents. Oxygen in atmosphere starting around 2. 7 billion years ago. Photosynthesis probably evolved early in prokaryotic history: relied on compounds like h2s for reducing power (modern plants usually split water like cyanobacteria) Cyanobacteria was very successful because of water. O2 is reactive and toxic so its abundance doomed many prokaryotes: strict anaerobes survived without adapting, others evolved protective mechanisms and cellular respiration.
