"stromatolitic carbonates and iron-rich argillites and shallow water sandstone" - so this would record our atmosphere being transformed into an oxygen rich one I guess... In NW Scotland we have the billion year old Torridonian sandstone making some spectacular mountains in Wester Ross.
I'd say by the time these rocks were deposited, even one billion years ago, this would be evidence for the largely completed oxygenation. Most of the oxygenation of the atmosphere was accomplished by 1.8 billion years ago, and I think the great majority of it was done by 2.2 billion years ago, recorded in the banded iron formations that contain so very much iron (as iron oxide, which took the free oxygen out of the water, and after the iron reactions were mostly done, the oxygen could go into the atmosphere). There are few banded iron formations younger than 1.8 billion. "Iron-rich" in these sedimentary rocks probably means less than 1% iron, and maybe even rather less than one-half percent. It doesn't take much iron oxide to make rocks look very red. Such iron-bearing sediments continue to form today, albeit in relatively small environments. Here are two postings I did about the oxygen event.
Really excellent blend of history and geology! Enigmatic Ediacaran life forms is an apt phrase. An evolutionary road not travelled but extraordinary. India's geology is fascinating! You could devote periodic essays on different countries' geologies and I wouldn't complain!
Thanks! I try (not too aggressively) to scatter other locations into these posts. There's one in the queue about South America, along with Arizona, Colorado, and Montana (which inevitably gets more coverage just because I know more about it and continue to explore and learn things about today).
"stromatolitic carbonates and iron-rich argillites and shallow water sandstone" - so this would record our atmosphere being transformed into an oxygen rich one I guess... In NW Scotland we have the billion year old Torridonian sandstone making some spectacular mountains in Wester Ross.
I'd say by the time these rocks were deposited, even one billion years ago, this would be evidence for the largely completed oxygenation. Most of the oxygenation of the atmosphere was accomplished by 1.8 billion years ago, and I think the great majority of it was done by 2.2 billion years ago, recorded in the banded iron formations that contain so very much iron (as iron oxide, which took the free oxygen out of the water, and after the iron reactions were mostly done, the oxygen could go into the atmosphere). There are few banded iron formations younger than 1.8 billion. "Iron-rich" in these sedimentary rocks probably means less than 1% iron, and maybe even rather less than one-half percent. It doesn't take much iron oxide to make rocks look very red. Such iron-bearing sediments continue to form today, albeit in relatively small environments. Here are two postings I did about the oxygen event.
https://historyoftheearthcalendar.blogspot.com/2014/01/january-20-banded-iron-formation-18.html
https://historyoftheearthcalendar.blogspot.com/2014/01/january-19-oxygen-crisis-2-billion.html
Really excellent blend of history and geology! Enigmatic Ediacaran life forms is an apt phrase. An evolutionary road not travelled but extraordinary. India's geology is fascinating! You could devote periodic essays on different countries' geologies and I wouldn't complain!
Thanks! I try (not too aggressively) to scatter other locations into these posts. There's one in the queue about South America, along with Arizona, Colorado, and Montana (which inevitably gets more coverage just because I know more about it and continue to explore and learn things about today).