BIO 200 Lecture Notes - Lecture 2: Protoplanetary Disk, Hadean, Meteoroid
22 Dec 2016
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4-3. 8 bya: earth went through heavy meteoroid bombardment. Causes hea(cid:448)(cid:455) (cid:272)(cid:396)a(cid:272)ks i(cid:374) it"s (cid:374)e(cid:449) su(cid:396)fa(cid:272)e. So steam escapes and additional gases and formation of volcanoes. These all results in the formation of an atmosphere. Afterwards, rain came; giving rise to oceans. New atmosphere: ammonia, methane, nitrogen, no free oxygen yet. Conditions only a little better: the hadean eon finally ends with the first life. Dating: fossils, strata of sedimentary rocks- layers, radioisotope dating- chemicals (decay, optical/luminescence- how long ago minerals were last exposed to day light, molecular data- time of divergence between different organisms. We divide earth into four unequal time periods: precambrian- super eon 4. 6 bya-543 mya, paleozoic era- 543mya-250 mya, mesozoic- 250 mya-65mya, cenozoic- 65mya- now. Simple unicellular organisms: for 3 billion years, that was all that was present, cyanobacteria mats/stromatolites: first, bacteria and archaea were already present on these early days on earth, even today, unicellular life dominates on earth.
