Page 35 - 新思维科学学生用书9 样章

1 Photosynthesis and the carbon cycle

Asteroids colliding with each other

Around 470 million years ago, scientists think that two asteroids collided with one another when they
were in space, somewhere in-between Earth and Mars.

The collision produced huge quantities of dust. The dust reduced the amount of light and heat from
the Sun reaching the Earth’s surface. This triggered an ice age. The Earth became much colder – the ice

caps spread much further from the poles and sea level fell.

Asteroids colliding with Earth

Around 67 million years ago, an asteroid collided with Earth. Researchers have identified an area on

the coast of Mexico where the asteroid impact took place. There was huge devastation close to where
the asteroid fell. It would have been like a massive bomb exploding, with shock waves and very high
temperatures spreading out from the crater.

But the collision affected the whole planet, not just the surrounding area, because it threw huge
quantities of rock and dust into the air. It would also have created a massive tsunami (a huge sea wave),
which could have spread across all of the Earth’s oceans.

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