Origins of Life

Today I learned the abiotic origin of organic compounds was established in the early 1800s, but the experiment wasn't actually intended to put forth a hypothesis for "abiogenesis"—or how life began on Earth.

The question of abiogenesis is the following one: how does so-called inanimate, non-living matter become animate, living matter? 

Friedrich Wöhler's so-called seminal contributions to organic chemistry would eventually lead to further hypothesis exploration about abiogenesis. Wöhler took two inorganic compounds—silver cyanate and ammonium chloride—and synthesized them to create urea, an organic compound that was previously believed to only be produced by living things carrying a "life force."

After Wohler's experiment, a large number of similar organic chemistry experiments would follow throughout the 19th century—and later those experiments would be followed by the Miller-Urey experiment.

The Miller experiment explored an origin of life scenario—simulating possible early conditions on Earth. By combining the gases methane (CH₄), ammonia (NH3), and hydrogen (H₂) with water—and exposing this amalgamation to electricity—various amino acids were produced, which are the building blocks of proteins. The related hypothesis is known as the prebiotic or primordial soup hypothesis.

But is the “prebiotic soup” theory a reasonable explanation for the emergence of life? Contemporary geoscientists tend to doubt that the primitive atmosphere had the highly reducing composition used by Miller in 1953. Many have suggested that the organic compounds needed for the origin of life may have originated from extraterrestrial sources such as meteorites. However, there is evidence that amino acids and other biochemical monomers found in meteorites were synthesized in parent bodies by reactions similar to those in the Miller experiment. Localized reducing environments may have existed on primitive Earth, especially near volcanic plumes, where electric discharges may have driven prebiotic synthesis. In the early 1950s, several groups were attempting organic synthesis under primitive conditions. But it was the Miller experiment, placed in the Darwinian perspective provided by Oparin’s ideas and deeply rooted in the 19th-century tradition of synthetic organic chemistry, that almost overnight transformed the study of the origin of life into a respectable field of inquiry. (via Prebiotic Soup—Revisiting the Miller Experiment)

The question of whether Earth's early atmospheric conditions were different from those in the Miller experiment is up for debate. The synthesis, however, continues to be a pioneering experiment in the study of abiogenesis—since it has further demonstrated that inorganic compounds can result in the formation of simple-to-complex organic compounds under circumstances potentially like those following asteroid impacts on Earth during the prebiotic atmosphere.

The hypotheses involving volcanic plumes and hydrothermal vents aren't the only abiogenesis hypotheses, of course. But they are particularly compelling ones, since one of the earliest forms of life on Earth was discovered in a ~3.42-billion-year-old subseafloor hydrothermal environment.

However, our last universal common ancestor is thought to have lived 4.2 billion years ago.