GLGY 209 Lecture Notes - Lecture 26: Banded Iron Formation, Silicon Dioxide, Neoarchean
3 May 2019
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Emergence of life on earth part 3. During neoarchaean, paleozoic, stromatolites were developed all over the earth. Stromatolites, by molecular oxygen from bacteria and cyanobacteria in their composition, expelled vast amounts of oxygen, and the atmosphere shifted its character from reducing to oxidizing. The transition happened over at least several 100 million years. Around the archaean proterozoic boundary, see a new type of rock around the world. Rocks that are silicious in nature, and devoid of these substances. Alternance between red (or brown, orange) layers with iron oxides and hydroxides, with green (or grey, white) rocks with silicious nature that are devoid of oxides or hydroxides. The fact that we have significant amount of oxygen in iron layers indicates presence of molecular oxygen in atmosphere. We like to think of this as a new type of rock that accumulated on all continents. This type of rock also occurred in small amounts, practically isolated, found earlier.
