This is CBS Eye in the World. I'm John Batchett with Oliver Morton, writing for the

Economist magazine about the thinking of James Lovelock, a man who worked with JPL in the

1960s. He was a physician, but also a keen on chemistry for discerning life on planets.

And our own planet started with what you'd have to say, complete radical conditions, different

from where we are now. From about four and a half billion years ago is the general assumption

that that's when we looked for the accretion of the planet. Perhaps between four and a half

and four we had the collision with the Mars-like planet, the creation of the moon, but I want

to get on to the fact, as Oliver Morton says, we had almost no oxygen about between four

and three billion years ago. So where did the oxygen come from, Oliver?

The oxygen came from the highest evolved form of photosynthesis, which is photosynthesis

in which creatures, and today we know them as cyanobacteria, if they're bacteria, and

algae and plants, if they're bigger things, which can split up water molecules to make

hydrogen and oxygen, and they can stick the hydrogen into carbon dioxide to make carbohydrates,

and that's what almost all the Earth's biomass comes from. And they get rid of the oxygen,

and it just percolates away. And when this started, the oxygen didn't get very far because

the environment was very avid for oxygen, so it all got used up quickly. But there came

a point sometime a bit after 2.5 billion years ago, when the oxygen basically broke its

bounds and got up into the atmosphere, and that's arguably the single most radical change

in the way the Earth acts and looks since it's early for formation, because it changes

the sort of minerals you have, it changes the chemistry of the oceans, it even changes

the colour of the sky, probably, because before there was oxygen in the sky, there would

have been permanent hazes of complicated, simple, but complex in some ways, hydrocarbons.

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