Labels:bulletin board | reckoner | sky OCR: that only about two billion vears ago after most of the reduced minerals in the sea were oxidized did atmospheric oxygen accumulate Between one and two billion years ago oxygen reached current levels creating niche for evolving life By examining the stability of certain minerals such as iron oxide or uranium oxide Holland has shown that the oxygen content of the Archean atmosphere was low, before two billion years ago it is largely agreed that the present day oxygen content of 20 percent is the result of photosynthetic activity Still, the question IS whether the oxygen content in the atmosphere increased gradually over time or suddenly Recent studies indicate that the increase of oxygen started abruptly between 2.1 and 2.03 billion years ago and the present situation was reached 1.5 billio ...
(.png)
