Oxygen. O2 is highly reactive and without constant replenishment will react out with elements such as iron in the lithosphere. There might have been SOME present prior to 3.5 billion years ago, but it would've been faint traces, with very little at surface level.
After 3.5 billion years ago, photosynthesis would have started to produce O2 in sufficient quantities for it to achieve significant concentrations.
After 3.5 billion years ago, photosynthesis would have started to produce O2 in sufficient quantities for it to achieve significant concentrations.
-
Oxygen, it caused the first mass die off when plants started producing it, the anaerobic life which had dominated the Earth died
-
Oxygen.......Respiration was anaerobic that time.
-
possibly oxygen....