One theory that is widely accepted about the origin of life on Earth is known as abiogenesis, or life arising naturally from non-living matter, such as simple organic compounds. The process is thought to have occurred approximately 4 billion years ago, possibly near hydrothermal vents deep in the ocean. The basic building blocks of life, including amino acids and nucleotides, would have formed from the reactions of simple compounds. Over time, these molecules would have become increasingly complex.