NUCLEOSYNTHESIS IN THE GALAXY

The colorful drama of Earth’s evolution begins with the formation of the Solar System. The Earth is, after all, merely one of several planets orbiting around the Sun, and the story of how the Earth formed cannot be told without describing how the entire Solar System was formed. Studying the formation of the Solar System in turn enables us to better understand the processes leading to the birth and death of stars, and the mechanisms by which all of the chemical elements in the universe were formed.

Thanks to nuclear physics, we now know how the chemical elements in the universe were made. Except for hydrogen, helium, and some lithium, which were created shortly after the Big Bang, all of the chemical elements were made by stars. Stars explode to end their life and eject the old and newly created elements into interstellar space. When a cloud of interstellar materials has high enough density, it will collapse under its own gravity to form a new star as well as a dusty disk around it, from which planets will emerge. A whole new cycle of chemical element synthesis (called nucleosynthesis) starts again within the central star, until the star consumes all the nuclear fuel and ends its life cycle explosively. In doing so, the universe becomes chemically more and more enriched with heavy elements.