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

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

1960s. It 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 4.5 billion years ago is the general assumption that

that's when we looked for the accretion of the planet. Perhaps between 4.5 and 4, 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 4 and 3 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 carbon

hydrates. 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 was that's arguably the single most

radical change in the way the Earth acts and looks since its early formation. Because

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

even changes the color 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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