c5bad647_Methane_Catastrophe__Gas
[Symbol] O¸3 [Significance] With the rise of atmospheric oxygen beginning about 2 1/2 billion years ago, this gas -- composed of molecules with three oxygen atoms -- was also produced. Ozone is found both in the lowest layer of the atmosphere, the troposphere, and the next highest layer, the stratosphere (about 10 to 50 kilometers, or 6 to 30 miles high). Much of the ozone in the troposphere today is produced by internal combustion engines and electrical devices, and it contributes significantly to smog. In the stratosphere, however, though it is only a very minor constituent, ozone absorbs much solar ultraviolet radiation, thus protecting living things from this highly energetic, extremely harmful radiation. (Water also protects against ultraviolet radiation, which is why life arose in the oceans. But only the rise of atmospheric ozone allowed living things to colonize the land.) [Gas] 
Ozone
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