Asteroid strikes
The orbits of some asteroids cross the Earth's orbit.
Small lumps of rock entering the Earthâs atmosphere burn up.
They form a shooting star and donât reach the Earthâs surface.
However, at various times during the Earth's history, asteroids have been large enough to hit the Earth.
When this happened, a tremendous amount of energy was released, throwing up billions of tonnes of dust.
This huge dust cloud blocked heat and light from the Sun, making the Earth very cold.
About 66 million years ago a giant asteroid travelling about 15 miles a second hit the coast of what is now Mexico.
The impact caused wildfires, tsunamis and put so much sulphur into the atmosphere that it blocked the sun.
This caused the Earth to cool rapidly bringing the extinction of the dinosaurs.
Scientists investigating the crater left by the asteroid strike found no sulphur remained at its core.
This supports the idea that when the asteroid hit, sulphur from the crater was released into the atmosphere.
There are other craters on the Earthâs surface which are a direct result of asteroid hits millions or billions of years ago.
These include:
- Vredefort Crater, Free State, South Africa - formed by asteroid strike 2 billion years ago.
- Sudbury Basin, Ontario, Canada - formed by asteroid strike 1.8 billion years ago.
- Ullapool, Scotland - formed by asteroid strike 1.2 billion years ago.
On Friday, April 13, 2029, the asteroid 99942 Apophis will pass just 19,000 miles above the Earth.
The lump of rock is about 350 m wide.
It will miss the Earth, but it is the closest known approach to Earth of any large asteroid this decade.