20 Jan
2016
20 Jan
'16
8:54 p.m.
="Warren D Smith" <warren.wds@gmail.com> [...] oxygen levels were indeed higher and lower in the past. https://en.wikipedia.org/wiki/Geological_history_of_oxygen and I do not know how solid their reconstruction of the past is, but they have one.
A graph with more detail that also marks big and less-big extinctions is linked from Wikipedia: http://www.nap.edu/openbook/0309100615/ I think the original source of this information might be Peter Ward, https://en.wikipedia.org/wiki/Peter_Ward_(paleontologist) author of the provocatively titled "Out of Thin Air" http://www.amazon.com/dp/0309100615