The inside of the Earth is hot because it contains radioactive atoms, mainly uranium, produced during the supernova which preceded the formation of the Solar System. Because of the energy released, radioactive decay releases . It is the source of heat in the , keeping the hot, and causing . It may also have caused the Earth to release the gases which made the .
Everybody on Earth receives radioactive radiation (correctly called ionizing radiation) from various sources. Almost all of it comes from the Earth and other natural sources, as shown in this chart.
Global Radiation Exposure data from HICARE
Notice that most man-made radiation comes from medical X-rays and other treatments. Only a tiny amount (about 1%) comes from pollution such as discharges from nuclear power plants.
Large atoms such as are too large to hold themselves together. They contain too many , which all repel each other, so the breaks apart into an and a nucleus. This type of keeps the and other planets warm. Because the rate of decay is predictable, it also allows us to rocks and other materials.
We have already seen that it is impossible to tell when any single will decay but, given a large number of nuclei, it is possible to predict how many will decay in a given time.
Because radioactive nuclei decay in a predictable way, we can use their decay to calculate the age of rocks, of remains of living tissue and other materials. In this way many of the dates given in this website have been worked out.
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