Most scientists belive that the solar system developed from a huge nebula (cloud of gas and dust) that once swirled aroind the sun. The sun itself may have been formed from the central part of this nebula. As the nebula whirled around the sun, it slowly flattened out. Sections of the cloud begsn to spin like eddies in a stream. Gas and dust collected near the centres of these eddies. The collections of gas and dust grew by attracting nearby particles of matter. They slowly developed into the spinning planets that now travel around the sun.

Immanuel Kant, Geraman philosopher proposed a nebular theory for the origin of the solar system in 1775. A french astronomer, Pierre Simon Laplace refined Kant's theory in 1776. Laplace suggested that the original nebula was much larger than the present solar system and left behind eddies of matter as it became smaller. This theory assumes that the earth was first gas and then liquid and finally cooled enough to have a solid crust.