The original synthesis of the chemical elements resulting from a huge explosion of undifferentiated energy that astrophysicists believe initiated the universe approximately 20 billion years ago, at least 7 billion years before the formation of the Milky Way galaxy (the so-called big bang theory). Information obtained with radiotelescopes indicates that temperatures were so inconceivably high in this continuum of radiation that the elementary particles that were undoubtedly present were unable to combine. As the continuum expanded rapidly after the original eruption, it cooled within a few minutes to the point where protons and electrons could unite to form hydrogen. After further cooling to 107C, thermonuclear fusion of hydrogen to helium occurred in a matter of seconds. But no more complex combinations took place in the young universe for several million years, until the shrinking cores of giant stars, many times the mass of the sun, raised their internal temperatures to 108C, high enough to fuse helium nuclei to form carbon. The heavier elements were eventually synthesized during explosions of supernovae, which produced temperatures in the range of 600 × 106C. Thus, the sequence of creation of the elements is believed to be hydrogen and helium, then after a few million years came carbon, oxygen, magnesium, silicon, sulfur, and iron; after yet another interval, the heavy metals were formed in another round of stellar explosions. All this occurred over a period of 5–7 billion years.See Fusion; Astrochemistry; Life, Origin; Origin.
