MadSci Network: Astronomy |
The Sun and the Earth are about the same age: four and a half billion years old. Astronomers believe that they formed from a cloud of spinning gas and dust. Most of it was pulled into the center and formed the Sun, while some of it was thrown outward into the shape of a huge, lumpy pancake. The Earth and all the other planets formed from the lumpy regions of this spinning disk. When the Sun gathered enough gas to heat up and turn on its central "engine", a huge wind came out from the Sun and blew away all of the gas between the planets, and most of the dust. The remainder of the dust had stuck to each other to form asteroids and comets, and for a long while these rocks bombarded Earth. They still do today, but not nearly so much and so often.
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