or abiogenesis or biopoiesis is the process by which life arose from inorganic matter. The word is usually used to describe the processes by which life on Earth originated. The earliest known life existed between 3.9 and 3.5 billion years ago, in the Eoarchean era, the time after the Hadean era in which the Earth was essentially molten.
Scientific hypotheses about the origins of life may be divided into several categories. Most approaches investigate how self-replicating molecules or their components came into existence. For example, the Miller–Urey experiment and similar experiments demonstrated that most amino acids, often called “the building blocks of life”, can be racemically synthesized in conditions thought to be similar to those of the early Earth. Several mechanisms have been investigated, including lightning and radiation. Other approaches (“metabolism first” hypotheses) focus on understanding how catalysis in chemical systems in the early Earth might have provided the precursor molecules necessary for self-replication.