The Dust-Cloud Hypothesis

The

universe contains huge clouds made up of very

large amounts of dust and 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 particles

together. As the dust cloud condensed, it began to

spin. It spun faster and faster and flattened as it

spun. It became shaped like a pancake that is

thick at the centre and thin at the edges. The

slowly spinning centre condensed to make the sun.

But the outer parts of the pancake, or disk, were

spinning too fast to condense in one piece. They

broke up into smaller swirls, or eddies, which

condensed separately to make the planets. The

forming sun and planets were made up mostly of

gas. They contained much more gas than dust. The

earth was far bigger than it is now and probably

weighed 500 times as much. The large body of

dust and gas forming the sun collapsed rapidly to a

much smaller size. The pressure that resulted from

the collapse caused 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.