All life on Earth shares a common chemistry. The bodies of dogs, dragonflies, dinosaurs, and diatoms are made up of carbon, calcium, oxygen, and a few other common elements. This material has been recycled over and over since life on Earth began. Some of the atoms that make up your body now were once a part of rocks, air, oceans, and other organisms that died long ago. But where did these raw materials come from in the first place? To answer that, we have to look at where the stuff of which our planet is made came from.
Our Earth formed, along with the Sun and the rest of the Solar System, approximately 4.6 billion years ago, from a cloud of gas and space dust known as a nebula. Astronomical observations have revealed huge numbers of nebulae, as well as stars of many different types at different stages in their lives, in our own Galaxy and beyond. Just like biologists, astronomers seek to understand the diversity of the subjects of their study first by classifying them. And as for biologists, studying birth, life, death, and environment are critical for astronomers.