Photosynthesis: the Cornerstone of Life.

Last week I checked our spare water bottles. I was a bit disappointed because one of them was green. Full of green algae indeed. What a nuisance! But on second thought, I reflected that without the ancestors of these green algae, you and I wouldnt be here to whinge about them.

Lets go back 2.7 billion years. The Earth is well and truly uninhabitable. The atmosphere is full of carbon dioxide, methane, ammoniac, a bit of nitrogen thank to volcanic eruptions, water vapour and no oxygen. The sun is 20% weaker than today but with the greenhouse effect, its still a tad less than 40 degrees out there. Cyanobacteria appear somewhere in the shallow ocean and kick start the Great Oxidation Event, doing the fantastic job plants still do today: photosynthesis.

Cyanobacteria are blue-green algae. They use visible light, water and carbon dioxide to make carbohydrates and oxygen. The more efficient green algae appear only 2 billion years later, followed by land plants another half billion years later.

Current plants like trees and cabbages use bits of green stuff called chlorophyll that look very much like the early cyanobacteria and produce exactly the same photosynthetic reactions. The cornerstone of life, indeed. However, about 70% of the Earth oxygen production (and carbon storage) still comes from the oceans. It is a great idea to plant trees for thousands of reasons, but it is an even better idea to stop polluting the oceans. Its a matter of life or death.




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