Earth Science

Earth Science - Anwsers to common questions

1. How did Earth and other planets form?

* It all started with a tremendous bang. Somewhere in our galaxy a star exploded, throwing out masses of gas and dust. This supernova, as these explosions are called, happened about 5bn years ago. The wreckage from the explosion then crashed into a nearby cloud of gas, bringing together the ingredients for our solar system to form.

Because the explosion was so energetic it made the dust mixture very hot and things began to cook. Little bits of dust began to cluster, making bigger and bigger lumps, and the mixture began to pull together under its own gravity.

Eventually the central lump became so hot and dense that it started to generate its own energy, igniting nuclear fires. This was the birth of our sun. The remaining dusty mixture swirled around the star, fanning out into a disc.

Gradually the sun grew in size and the dusty disc cooled. Over millions of years the dust clustered into grains, then lumps, boulders and eventually planetesimals - chunks of rock big enough to have their own gravitational field. Some of these planetesimals became the embryonic forms of the planets in our solar system today.

Slowly these rocky planets began to organise themselves, settling at a comfortable distance from the sun and finding their own orbit. Earth found its path as third planet from the sun. In the early days rocky pile-ups were still common, leaving craters on the surface of all of the planets.

One of these collisions, about 4.5bn years ago, is thought to have very nearly destroyed the Earth, and was probably responsible for our moon. A large planetesimal, about the size of Mars, gave Earth a glancing blow, chucking a chunk of Earth's crust out into space. Some of the planetesimal merged with Earth, while the ejected lump started its own orbit around Earth and became the moon.

Evidence for this theory comes from samples of moon dust, showing that the moon is made of...