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Heavy Elements

Life, as we've mentioned earlier, uses many different elements, including hydrogen, carbon, nitrogen, oxygen, and phosphorous. How do we collect all those elements in one place?

Hydrogen is the most abundant element in the universe, created in vast amounts by the Big Bang. Helium was also created in the Big Bang - about a quarter of the mass of the early universe was helium - as well as a very small amount of Lithium. All of the other elements were not created in the Big Bang - instead, they are created in the cores of stars as they burn and explode, in a process called nucleosynthesis. Without stars and supernovae, we would never have the elements we need for life.

We can see these heavier elements in interstellar clouds. However, they are very sparsely distributed there. These clouds may only have a thousand molecules per cubic centimeter, whereas Earth's atmosphere is about twenty-quadrillion times as dense. Without enough atoms from heavy elements in the same place at the same time, only the most simple compounds can form.

Gas giants have more than enough gravity to pull in heavy elements, but life faces other difficulties there. The heavy elements (lithium and above) fall down toward the core of the planet, where immense temperatures break apart most compounds as soon as they are formed. The upper layers of gas giants contain mostly hydrogen and helium, which cannot support the complex chemistry needed for life.

Terrestrial worlds, on the other hand, provide an environment where heavy elements can collect on the surface, without extreme temperatures or pressures. The movement of the atmosphere and oceans helps these elements to mix and collect over short timescales. Over longer timescales, geological processes such as plate tectonics help to bring heavy elements to the surface.

Солнечная система и ее тайны