EESB15H3 Lecture 13: Proterozoic Eon Lecture Notes, Oct. 30
4 Nov 2017
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Figure 1: geologic eons as a proportion of geologic time. A number of cratons, made from the accretion of geologic terranes (granite-greenstone belts). Mainly anoxic atmosphere, low levels of oxygen in the oceans. There"s evidence for decreasing ocean anoxia and an increasingly oxic atmosphere. Banded iron formations imply the presence of free oxygen in the water. Possibly as old as 2. 7 billion years ago. Grypania (2. 1 ga, impressions of multicellular eukaryotes). Acritarch (1. 8 or 3. 2 ga, single-celled protists). Figure 3: endosymbiosis and the origin of eukaryotic cells. An aerobic bacterium and a larger host bacterium united to form a mitochondria- containing amoeboid. An amoeboflagellate was formed by a union with a bacterium. Amoeboflagellate gave rise to the animal fungi and protist kingdoms. The plant kingdom originated when blue-green algae became plastics within an amoeboflagellate. Figure 4: evidence for pre-orogeny rifting, spreading, and a passive continental margin (before 2. 0 ga). The southern province is the passive margin of arctica.
