What evidence from rocks show that life has changed the atmosphere?
I аm responsibility a science scheme аnd i hаνе tο find out hοw аnd whаt rocks hаνе provided prove thаt аѕ life hаѕ formed, thе atmosphere hаѕ altered. Example: banded iron formations аѕ found іn Minnesota’s Iron Range.
Prove from the Rock Record:
(1) Iron (Fe) i s exceptionally reactive with oxygen. If we look at the oxidation state of Fe in the rock record, we can infer a fantastic deal about atmospheric evolution.
(2) Archean eon – Find occurrence of minerals that only form in non-oxidizing environments in Archean sediments: Pyrite (Fools gold; FeS2), Uraninite (UO2). These minerals are easily dissolved out of rocks under present atmospheric conditions.
(3) Banded Iron Formation (BIF) – Deep water deposits in which layers of iron-rich minerals alternate with iron-poor layers, primarily chert. Iron minerals contain iron oxide, iron carbonate, iron silicate, iron sulfide. BIF’s are a major source of iron ore, because they contain magnetite (Fe3O4) which has a higher iron-to-oxygen ratio than hematite. These are common in rocks 2.0 – 2.8 Ga, but do not form today.
(4) Red beds (continental siliciclastic deposits) are never found in rocks older than 2.3 B. y., but are common during Phanerozoic time. Red beds are red because of the highly rusty mineral hematite (Fe2O3), that probably forms secondarily by oxidation of other Fe minerals that have accumulated in the sediment.
Prove linking rock to life comes in the form of fossils that had to have been formed under conditions that would have required significant oxygen, and containing organisms that may possibly only have lived on an abundance oxygen source (or so biologists and paleontologists believe, at least). Finally, contemporary oxygen-needing life versus the very ancient anaerobic organisms that are still alive, “living fossils” (not really, but for ease of conversation).
Small graph down there should help.