MOToday's leading theories concerning Earth's birth have more in common with the early ideas of Kant and Laplace than those of the later collision theorists.

According to the most-accepted scenarios, the solar system began when a huge, old star exploded as a SUPERNOVA, sending heavier elements like carbon, lithium, and beryllium - as well as other debris - flying out into interstellar space, where they mixed with the abundant hydrogen there. This cocktail of gases became the NEBULA from which Earth and other planets formed.

About 5 billions years ago, this rapidly expanding nebula began to cool, contract, and spin more quickly. It became a somewhat flattened disk called a solar nebula.

Most of the mass of this nebula scrunched into its center. The resulting pressure created enough heat to set the center ablaze, creating a "protosun." Away from the center, where temperatures were cooler, whirlpools formed, and grains. Some of the grains, caught within the whirlpools, collided and stuck together. Through this process of accretion, the gathering bits and pieces built up into larger and larger objects, eventually forming planets.

The scientist long believed that sometime during the end  of this process of accretion, a random collision blasted off a chunk of Earth large enough to become MOON. But in 1995, a chemical study of the Moon's surface revealed that it contains much less iron than does Earth. This strong evidence that it is not a former piece of Earth. Astronomers says that the Moon was originally a large, independent planetisimal that smashed into Earth. Following the collision, a large chunk of this planetesimal bounced back into space and settled into its present orbit. around the same time, the other planets in the solar system took shape, complete with their personal satellites, or moons. 


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