Many different ideas have been suggested, ranging from the hand of God to the ‘Big Bang Theory’. ‘Big Bang’ suggests that the Universe was formed 20,000 million year’s ago by the sudden explosion of a small mass of material which was incredibly heavy. These materials where called atoms. Where did they come from in the first place? It seems unlikely that anyone will ever have the final answer.
On the other hand, once we can assume that the Universe does indeed exist, it becomes a little easier to think about the formation of our very own planet because we already have the building material available.
For many years, the most accepted idea concerning the formation of the Earth was the result of a scientist called Kelvin in 1862. He suggested that the Earth has cooled from a melted, that is, a molten, mass. He put forward this idea partly because it had been proved definitely by that time that the Earth is losing heat, and also because this seemed to provide an explanation for the origin of volcanoes spewing their red hot lava from the Earth’s interior.
More recently, however, a great deal of evidence has been gathered, indicating that the planet was probably never completely melted. In fact, the most popular theory nowadays is that the Earth, and also the rest of the solar system, where formed from the coming together of a cloud of dust and gas. This was probably a result of the gravitational attraction which all objects have for each other. Scientist think this occurred about 6000 million years ago. This means that the Earth probably formed cold rather than a molten ball.
Science knows from the evidence of deep mines, however, that the Earth becomes very much hotter towards the centre. Where does the heat come from? Certainly, it must have become hot enough to melt many of the original materials. Scientists think this heat has a twofold origin. When the Sun contracted at the very beginning, its centre become hot. This set off a decay of certain radioactive waves which released a great deal of heat. It seems likely that the first of the Earth’s rocks were formed from their melted parent materials about 4500 million years ago.