Uranium´s cosmic life-cycle

The Earth contains about one hundred natural elements, the lightest being hydrogen and the heaviest uranium.

The lightest elements, hydrogen and helium, were created in the Big Bang. Uranium and other elements heavier than iron were created in supernova explosions and mixed with interstellar gas and dust matter. New stars were created from the clouds of interstellar matter that contracted into clusters.

Our Sun was created in this way about five billion years ago. The centre of a revolving cloud coalesced into the Sun, while the outmost parts formed the planets and other components of the solar system. Terrestrial planets composed of heavy elements, such as the Earth, were formed near the Sun, and gas giants, such as Jupiter and Saturn, were formed further away.

The constituents were arranged in the evolving Earth according to their weight: the heaviest in the middle and the lightest on the outer shell. Heavy elements - uranium, iron and nickel - sank into the Earth´s interior. To this day, radioactive fission heats the Earth´s core and keeps it molten. There was more uranium in the Earth´s early years, but being radioactive matter, some of it has decayed into other substances.