Currently, there are two theories about how life originally formed in the universe: abiogenesis and biogenesis.

The precursor to the theory of abiogenesis was originally posited by Aristotle in the 4th century. His theory, called spontaneous generation, proposed that fully developed life rapidly arose from non-living matter, such as inorganic compounds or other inanimate substances. Although his theory was eventually disproven, the concept was adapted into the modern theory of abiogenesis - that simple life gradually evolved into complex life from non-living matter.

The theory of biogenesis originated in the middle of the 19th century and is still believed nowadays. It hypothesizes that complex life only arises from pre-existing living things through means of reproduction. It is theorized that life on Earth initially developed through abiogenesis before switching to biogenesis.

Spontaneous generation is an old theory that doesn't work, and abiogenesis is the right idea that may describe where life comes from. Unlike biogenesis, abiogenesis has neither proven nor disproven - as it has never been observed. Even though modern biology focuses more on biogenesis, abiogenesis is significantly researched in the field of astrobiology - a science that studies life outside Earth.