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.
1. A gigantic cloud of dust and gas drifted in space. Gravity pulled
much of the gas into a huge ball in the cloud’s center. This was the
beginning of our 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 couldn’t stay hot. It began to cool. And
when melted rock and metal cools,
2. In other parts of the cloud, gravity pulled dust and gas together
forming blobs.
3. The blobs of dust and gas slowly shrank into tight-packed balls.
This was the beginning of the earth and other planets.
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.
