If you trace our origins back, not only to the beginning of life on earth but to the formation of our solar system, you come to the conclusion that we are literally made of star dust. Our sun is a second generation star, formed from the debris left over when a first generation star came to the end of it's life and then exploded. Our Sun and all the planets of our solar system were formed when gravity pulled that debris together again.
Synthesis of the Elements
The first generation star was formed early in the life of the Universe and was formed from hydrogen(the first element), collapsing to the point where a temperature hot enough for hydrogen fusion was achieved within the star's center. The energy flowing out of the star from the fusion worked against the gravity that was trying to collapse the star further, and the collapse stopped. As this super large fusion reactor converted matter to energy, it converted the hydrogen into helium(the second element). This continued for billions of years until less hydrogen was available in the star, and the conversion rate slowed down. This slow down meant that there wasn't as much energy flowing outward, and so the collapse of the star began again.
This increased the core temperature further until a temperature hot enough for helium fusion was achieved, once again creating more energy as the helium is converted to lithium(the third element) and stopping the collapse. You can see how this can continue, with helium fusion giving rise to lithium fusion, then beryllium, boron, carbon fusion and so on. This continues until the star is making iron from the fusion of lighter elements, but it doesn't go beyond iron. When the elements making iron from fusion run low, the star's collapse cannot be stopped and it implodes until it either goes nova or, if the mass is large enough, supernova. The tremendous energy of these star explosions is what makes the elements above iron, and so the debris has all the elements.
The Debris Coalesces and forms Second Generation Stars
The powerful explosions of the nova and supernova results in an expanding cloud of debris know as a nebula. It can take millions of years for gravity to slowly slow down the expansion from the original explosion.
But slowly, this does happen, and so the nebula are the nurseries for second generation stars like our sun and their planets, which are made up of all the elements. Should a planet have the right distance from the new star and have the other right conditions, life evolves, as it has on our earth.
We are stardust!
