History of research into the origin of life

The advantage is that life is not required to have formed on each planet it occurs on, but rather in a single location, and then spread across the galaxy to other star systems via cometary or meteorite impact.

[3] Evidence for this is scant, but it finds some support in studies of Martian meteorites found in Antarctica and of extremophile microbes' survival in outer space tests.

Spontaneous generation, the first naturalistic theory of abiogenesis, goes back to Aristotle and ancient Greek philosophy, and continued to have support in Western scholarship until the 19th century.

Aristotle stated that, for example, aphids arise from dew on plants, flies from putrid matter, mice from dirty hay, and crocodiles from rotting sunken logs.

Van Leeuwenhoek disagreed with spontaneous generation, and by the 1680s convinced himself, using experiments ranging from sealed and open meat incubation and the close study of insect reproduction, that the theory was incorrect.

In On the Origin of Species, he had referred to life having been "created", by which he "really meant 'appeared' by some wholly unknown process", but had soon regretted using the Old Testament term "creation".

While differing in details, these hypotheses are based on the framework laid out by Alexander Oparin (in 1924) and John Haldane (in 1929), that the first molecules constituting the earliest cells .

No new notable research or hypothesis on the subject appeared until 1924, when Oparin reasoned that atmospheric oxygen prevents the synthesis of certain organic compounds that are necessary building blocks for life.

The underlying hypothesis held by Oparin, Haldane, Bernal, Miller and Urey, for instance, was that multiple conditions on the primeval Earth favoured chemical reactions that synthesized the same set of complex organic compounds from such simple precursors.

[34][35][36] In 1952, Stanley Miller and Harold Urey performed an experiment that demonstrated how organic molecules could have spontaneously formed from inorganic precursors under conditions like those posited by the Oparin-Haldane hypothesis.

The Miller–Urey experiment used a highly reducing mixture of gases—methane, ammonia, and hydrogen, as well as water vapor—to form simple organic monomers such as amino acids.

After one week, it was found that about 10% to 15% of the carbon in the system was then in the form of a racemic mixture of organic compounds, including amino acids, which are the building blocks of proteins.