[felix]

felix  asked the Naked Scientists:
Dear Chris,

I am a long time listener of your lively podcast. Thank you for making us available the service for free!
   
I've heard that marine algae, especially photo-autotrophic picoplanktons, release a vast majority of oxygen in the air we breath. Given that ocean comprises almost 73% of earth surface and the abundance of these tiny plants in ocean, I was wondering how many percent do they actually contribute to the total oxygen production in earth. Some say roughly 70% and others even put it 91%. I was also wondering if all the terrestrial plants got destroyed, will it lead to a real drastic change in oxygen level (not to mention other eco-geological disasters).  

Thank you,
Felix Bast, Japan.
What do you think?

[another_someone]

One major difference it would make is that the destruction of land plants would lead to the destruction of land animals, which probably (especially if we include man as a land animals) contribute a disproportionate share of consumption of oxygen (also, the destruction of land plants would prevent forest fires, which are another great consumer of oxygen).

[JimBob]

The major episodes of low oxygen in the earth's history are associated with oceans in which there is no Oxygen. Thus, I would tend to believe the earth would be just fine - the oceans would be dead except for a small layer near the surface and the pelagic(surface layer) critters in the oceans, both plant and animal, which includes fish, would still be very full of life.

In the past, these conditions have been existent for a long period of time - the Ordovician, Devonian, Carboniferous, and Cretaceous black shales are the source of most if not all of the petroleum found in the world.

As the creatures in the pelagic layer of the ocean die they fall to the bottom and because of the lack of oxygen, the organic material is not re-introduced into the ocean but sequestered in the shale. Later, when buried, the shales produce oil and gas. It is squeezed into the rocks below or above to form oil and/or gas reservoirs.