“Astronomical Alchemy” – the origin of elements
While hydrogen and helium were produced in the Big Bang, the origin of heavier elements, the silicon in rocks, the iron in our blood, and the oxygen we breathe, lies in the lifecycle of stars.
Nuclear fusion reactions in stars produce energy and cause them to shine. Small stars convert hydrogen into helium. In medium-sized stars like our Sun, when hydrogen becomes depleted, fusion reactions can convert helium into oxygen and carbon. For massive stars, greater than five times the mass of the Sun, when hydrogen becomes depleted helium atoms can be fused into carbon and oxygen, followed by the fusion of carbon and oxygen into neon, sodium, magnesium, sulfur and silicon. Later reactions transform these elements into calcium, iron, nickel, chromium, copper and others. When these old, large stars with depleted cores collapse and become supernova, they create the heavier elements (all the natural elements heavier than iron) and spread them into space, forming the basis for life.