How do we know the Earth is four billion years old?

The Earth is the only planet in our solar system where humans live.

It's the fifth largest planet in the solar system, over 70 per cent of it is covered by water and it's about 93,000,000 miles away from the Sun!

The Earth is an incredible source of life that has been around for 4.5 billion years, but have you ever wondered how exactly we know this?

This was the burning question on 14-year-old Ayshah's mind and physicist Professor Brian Cox is on hand to give us all the details.

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