How was the earth born ?

Why is the earth shaped like a ball ? Why isn't it shaped like a block ? Or why isn't it round and flat, like a pie ? Why does it spin ? And why does it whirl around and around the sun ?

Most scientists think that the answers to these questions are part of the story of how the earth was born. They think it is a story that began billions of years ago, with a giant, spinning cloud in space.

There are many such clouds in space right now. They are made up of chemicals in the form of gas and dust. Scientists have found that some of these clouds seem to be turning into new stars. And scientists think that, about five billion years ago, our sun and its planets were formed from just such a cloud.

The cloud was hundreds of millions of miles (kilometers) wide ! The force of gravitation pulled it into the shape of a huge, flat wheel. And it spun around and around, just like a wheel.

Gravitation slowly pulled the cloud together. Most of the gas collected in the middle of the cloud. It formed a lump that got bigger and bigger. As the lump grew, its gravity became stronger. Then it pulled more and more gas into itself. Because gravity pulls equally from all directions, the lump was squeezed into the shape of a round ball. This was the only shape it could take.

After a long while, there was a gigantic ball of gas in the middle of the wheel-shaped cloud. This was the beginning of the sun.

Farther out, in the rest of the cloud, other balls were forming as gravity pulled bits of dust and gas together. After a while, most of the cloud was used up. There were only balls of gas and dust, whirling around the sun. They were spinning and moving around the sun because the cloud they were made from had been spinning. These balls were the beginning of the earth and the other planets and moons. So that is why the earth is a spinning ball that whirls around the sun.

But if the earth was once a spinning ball of dust and gas, how did it become a ball of rock and metal ?

As earth's gravity pulled more dust and gas in, everything was squeezed together - tighter and tighter and tighter ! This made the ball grow hotter and hotter ! It became so hot that the bits of dust in it, which were mostly rock and metal dust, melted together. The earth became a glowing ball.

But the outside of the earth could'n't stay hot. It began to cool. And when melted rock and metal cools, it gets hard. So the earth became a ball of hard rock and metal, as it is today.

But the earth still hasn't cooled off. The middle is still fiercely hot, and part of the inside is still melted.

There are many other beliefs about how the earth was born. The book of Genesis in the Bible says that God created the earth and all living things. But no one actually knows how it happened