c5bad647_Methane_Catastrophe__Gas
[Symbol] O¸2 [Significance] A waste product of oxygenic photosynthesis. Chemically active; it combines readily with other elements. Not present in Earth's early atmosphere because oxygenic photosynthesizers (specifically, phytoplankton) had not yet evolved. Today's atmospheric level (about 21%) is maintained by the continuing activity of phytoplankton and terrestrial green plants. Required by all aerobic organisms. Highest level, during the Permian, was 30-35%. This level fell rapidly at the end of the Permian and during the Early Triassic, to perhaps 12%. [Gas] 
Oxygen
O x y g e n
W a t e r v a p o r
C a r b o n d i o x i d e
M e t h a n e
H y d r o g e n s u l f i d e
H y d r o x y l
O z o n e
Methane Catastrophe
Gas