Scientist have models in order to explain how
the universe and the planets formed, including
Earth. According to the best model we have, the
planets in our solar system formed from gas and
dust surrounding the sun. Every object exerts
force on other objects through gravity
(gravity is the force which keeps all of the
planets in orbit around the sun). It's easy
to recognize that the earth exerts a gravitational
force on you, but you also exert the same
gravitational force on the earth.
Dust particles, even though they are very
small, were attracted to each other by gravity.
There may have been other processes that helped as
well, such as static electricity. Static
electricity is often created when two objects are
rubbed together, and electrons from one of the
objects rub off onto the other.
Electrical attraction is a much stronger
force than gravity, so this might have sped things
along. Once the process got rolling, dust
particles collected into rocks (or at least
"snowballs" of dust), then into boulders, then BIG
boulders, and eventually the boulders collided
with each other and formed planets, like
Earth. Big planets have a lot of gravity, so
they pulled in the rest of the nearby dust.
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