Do We Really Need the Moon? Page #2

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At this time, the Earth had no Moon,

it was orbiting the Sun alone

and it was being assaulted by rocks and comets.

Today, there are no scars left from this cosmic pinball.

But to get a sense of the damage that was done,

I've come to the Arizona Desert,...

..to a great hole in the ground.

This is a beautiful crater,

a near perfect circle a mile in diameter.

It was formed when a meteorite crashed into the Earth a mere 50,000 years ago.

That's nothing on the timescale we're talking about,

but it's amazing how much damage that one passing rock can cause.

The early Earth was bombarded with rocks. It must have been mayhem.

And then along came something much, much bigger.

Another planet the size of Mars, drifted into the path of Earth.

It was on a collision course.

It hit the young Earth with a glancing blow.

Imagine the power released by such a collision.

The impact sent a mass of liquid rock into orbit.

This debris coalesced into a ball.

And the Moon was formed,

just 14,000 miles away from the early Earth.

This was the closest point it could have been.

Any closer, and gravity would have pulled the debris crashing back to Earth,

and our moon wouldn't exist.

Today the Moon is just a rock reflecting the sun's light,

but back then it was a molten sphere, burning brightly.

It must have looked amazing, an enormous orange disc in the sky.

Imagine the scene.

The first moonrise over the early Earth.

Our world was no longer alone.

It had a huge, powerful neighbour.

And ever since, this has been a very different type of planet.

The collision that created the Moon reset the basic chemistry of Earth.

And Earth Mk II was a place on which life could begin.

The collision released huge quantities of metal from the Earth's core,

one particular metal that would help change the atmosphere of our planet.

I'm talking about iron.

Iron is incredibly reactive.

Leave some out in the garden and it will rust.

It also combines with other chemicals to release gases

such as methane, carbon monoxide and hydrogen.

Today we see these gases as toxic and rather unpleasant.

But in the early Earth this was the very stuff of life.

In the 1950s, American chemist Stanley Miller did a classic experiment.

He took a cocktail of these gases and tried to simulate conditions on the early Earth,

adding electricity to mimic the power of lightning.

And what emerged, to everyone's surprise, was a flask of slime,

which turned out to be full of amino acids.

Like iron, amino acids are essential for life.

They are the raw material from which proteins are made.

And this great chemist was able to produce them using gases that were available on the early Earth.

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