Beginning of Essay
The universe contains huge clouds made up of very large amounts of dustand gas. About 6,000,000,000 (billion) years ago, one of these clouds began to condense. Gravitation--the pull that all objects in the universe have for one another--pulled the gas and dust p ....

Middle of Essay
.... the sun to become very hot and to glow brightly. The newly born sun began to heat up the swirling eddy of gas and dust that was to become the earth. The gas expanded, and some of it flowed away into space. The dust that remained behind then collected together because of gravity. Although the shrinking earth generated a lot of heat, most of this heat was lost into space. Therefore, the original earth was most likely solid, not molten. This hypothesis was developed by a scientest, Harold C. Urey in 1952. It is also known as the Urey's hypothesis. He showed that methane, ammonia, and water are the stable forms of carbon, nitrogen, and oxygen if an ....