The Miller–Urey experiment (or Miller experiment) was an experiment in chemical synthesis carried out in 1952 that simulated the conditions thought at the time to be present in the atmosphere of the early, prebiotic Earth. It is seen as one of the first successful experiments demonstrating the synthesis of organic compounds from inorganic constituents in an origin of life scenario. The experiment used methane (CH4), ammonia
(NH3), hydrogen (H2), in ratio 2:2:1, and water (H2O). Applying an electric arc (the latter simulating lightning) resulted in the production of amino acids.
Portrait photograph of Alexander Oparin
Stanley Miller in 1999, posed with an apparatus like that used in the original experiment
The surface of Titan as viewed from the Huygens lander. Tholins, complex particles formed by UV irradiation on the N2 and CH4 atmosphere, are likely the source of the reddish haze.
Conceptual figure from Wogan et al. (2023) depicting three stages phases of atmospheric chemistry after a large asteroid impact on the Hadean Earth. In phase 1, the impactor vaporizes the ocean, and H2 is generated after iron delivered by the impactor reacts with hot steam. In phase 2, H2 reacts with CO2 to produce CH4 while the atmosphere cools for thousands of years and steam condenses to an ocean. Phase 3 represents the Miller-Urey atmosphere that persists for millions of years, where N
In biology, abiogenesis or the origin of life is the natural process by which life has arisen from non-living matter, such as simple organic compounds. The prevailing scientific hypothesis is that the transition from non-living to living entities on Earth was not a single event, but a process of increasing complexity involving the formation of a habitable planet, the prebiotic synthesis of organic molecules, molecular self-replication, self-assembly, autocatalysis, and the emergence of cell membranes. The transition from non-life to life has never been observed experimentally, but many proposals have been made for different stages of the process.
Stromatolites in the Siyeh Formation, Glacier National Park, dated 3.5 Gya, placing them among the earliest life-forms
Modern stromatolites in Shark Bay, created by photosynthetic cyanobacteria
The Cat's Paw Nebula is inside the Milky Way Galaxy, in the constellation Scorpius. Green areas show regions where radiation from hot stars collided with large molecules and small dust grains called "polycyclic aromatic hydrocarbons" (PAHs), causing them to fluoresce. Spitzer Space Telescope, 2018.
The earliest known life forms are putative fossilized microorganisms, found in white smoker hydrothermal vent precipitates. They may have lived as early as 4.28 Gya (billion years ago), relatively soon after the formation of the oceans 4.41 Gya, not long after the formation of the Earth 4.54 Gya.