Unfortunately, he was unaware of radioactive decay and neglected its contribution to the total heat being lost by the Earth. Salt in the Oceans - Estimates of about 90 MY based on this method. It neglects all the salt in trapped in sedimentary rocks. Very inaccurate due to problems determining the total thickness of all sediments accumulated through geologic time. Radioactive Decay Matter - Anything that occupies space and can be seen by the human eye.
Scientists realize there are particles smaller than the eye can see.
Atom - The smallest particle of which matter is composed. Scientists could not see atoms, but over centuries they devised a model of the atom based on simple logic. The latter revolved in orbitals around the former, analogous to the revolution of the planets around the Sun. From this was born the concept of the element. Element - A unique combination of protons, electrons and neutrons.