EAES 101 Lecture 23: Geologic time:History of the Earth
2 Nov 2016
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During what geologic age does life first appear: archaean. Stromatolites are layered structures that may be produced by the activity of: cyanobacteria. 2. 5 gya 542 ma: protero=first; zoic= life, named before archean life was discovered, ~2 ga (2. 5 to . 542 ga); almost of earth history, the unfamiliar archean world changed to , larger continental landmasses, an oxygenated atmosphere. The proterozoic eon: new continental crust formed, but at slower rates, 90% of earth"s continental crust by the middle proterozoic, continents grew by addition of volcanic arcs, continents cooled and strengthened to become cratons. The proterozoic eon: continental collision created precambrian supercontinents, rodina-formed ~ 1 ga, pannonia- a short-lived supercontinent ~600 ma. North american context: bottom-most layer of the grand canyon was depositied, granites [vishnu unit, 1. 8-1. 6 ga. Iclicker: what important event occurred during the proterozoic eon: a rise in atmospheric oxygen allowed the development of diverse and complex life forms.
