As we explored in Formation of our Solar System, the raw materials for life all ultimately came from space. The early Universe was composed mostly of hydrogen, with a little helium and lithium, as well as trace amounts of heavier elements. Successive generations of stars have processed hydrogen into heavier elements. Through nuclear fusion in the cores of stars, through dust and “soot” produced in the atmospheres of massive stars, and through the violent deaths of stars in supernova explosions, the Universe has been enriched over cosmic time with elements like oxygen, calcium, and iron that were later incorporated into subsequent generations of stars.
Chemical reactions in space have also combined some of these elements into larger molecules. Carbon dioxide, ammonia, benzene, and even amino acids have been detected in stars and gas in space, and organic molecules have also been found in meteorite and comet samples. The material that makes up our own bodies was present in the nebula from which the Solar System formed, including the calcium in our bones and the iron in our blood, which came from stars that died billions of years ago. We are literally made of stardust!