Nucleosynthesis is the process of building nuclei of atoms heavier than hydrogen. The Big Bang produced hydrogen, helium, and some lithium, but all later creation of higher weight atoms has occurred in the hearts of stars via nucleosynthesis. All elements heavier than hydrogen of which Earth and humans are made were forged in stellar interiors by nucleosynthesis.
Until the second half of the nineteenth century, astronomy was principally concerned with accurately describing the movements of planets and stars. Developments in the electromagnetic theory of light in the late nineteenth century along with the articulation of quantum and relativity theories in the early twentieth century, however, gave astronomers the tools they needed to probe the inner workings of the sun and other stars. In the first two-thirds of the century, astronomers and physicists unraveled the life cycles of most types of stars and reconciled the predictions of physical theory with astronomical observation. Insights into the birth and death of stars led to the stunning conclusion that Earth and all life upon it, including human beings, are in a direct and physical sense a product of stellar evolution. In astronomy, the term "evolution" is used to name the orderly process by which individual stars change as they age: stellar evolution is unrelated to biological evolution. more