2200 – 2100 million years ago

Year twenty-five
Oxygen escapes into the atmosphere and turns iron on land rusty

Oxygen escapes into the atmosphere

Even when the Earth had reached 24 years old (about 2200 million years ago), there was still no life on land except bacteria that lived in ponds and within the protection of the soil. There wasn't enough oxygen or ozone in the atmosphere to stop the harmful ultraviolet radiation from the sun reaching the Earth's surface. Anything that tried to live on the surface of the land, outside the protection of the water or soil, would have been quickly killed.

But very slowly, bacteria in the oceans were making more and more oxygen, which gradually found its way into the air (the Earth's atmosphere).

By the time Earth was 25 years old (about 2100 million years ago), there was enough oxygen to make the iron in some of the rocks on land go rusty. The rusty rocks are called 'red beds'.


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