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Fossil Energy: Nuclear energy
In the mid-20 physicist harnessedd the energy released from the decaying nuclei of radioactive isotopes (nuclear fission). Now they are attempting to tap the energy produced when atomic nuclei are fused together (nuclear fusion). These energy sources may provide a twenty-first-century solution to the inevitable exhaustion of fossil fuels, however we know that they are not without significant danger.
The key element in the development of nuclear energy is uranium. The average uranium content in the rocks of Earth's crust is about 2 ppm. It is concentrated in deposits by late magmatic segregation and occur in veins associated with intrusive igneous rocks. Decaying uranium235 nuclei release neutrons. When this process occurs in an material enriched in Uranium235 release neutrons bombard other uranium235 nuclei which in turn undergo fission producing heat and more neutrons which then bombard neighboring uranium235 nuclei in a chain reaction. Uranium235 account form only 0.7% of natural uranium, whereas non-fissionable Uranium238 makes up 99.3%. The reserve in Uranium 235 may be sufficient to power the world's 575 nuclear power plants for only 30 year or so.

Physicist try to produce fissionable plutonium 239 from non-fissionable Uranium238, the problem is that Plutonium239 is a weapons-grade nuclear material. The other drawback of nuclear fission is the production of radioactive waste that must be stored in a save place for hundred to thousand of years.

Nuclear fussion occurs when extremely high pressure and temperature cause the atomic nuclei of ultra-light elements to fuse together to from hearvier atoms. This is the same process that that powers the Sun's thermal furnance. This process releases an enormous amount of heat energy that can be used to convert water to steam driving turbines to produce electricity. The principal fuel of fusion is hydrogen one of the most abondant elements and rather than toxic radioactive waste the product of fission is helium a harmless inert gas. Fusion;s potential is enormous: the energy that can be produced from 1 cubic kilometer of seawater exceeds the total energy stored in the world's oil reserves. The main problem is that a tremendous amount of energy is required to produce fussion, and at that stage this process is not commercially viable.