What is Theory of Abiogenesis?
Abiogenesis, the idea that life arose from nonlife more than 3.5 billion years ago on Earth. Abiogenesis proposes that the first life-forms generated were very simple and through a gradual process became increasingly complex.
Biogenesis, in which life is derived from the reproduction of other life, was presumably preceded by abiogenesis, which became impossible once Earth’s atmosphere assumed its present composition.
Although many equate abiogenesis with the archaic theory of spontaneous generation, the two ideas are quite different. According to the latter, complex life (e.g., a maggot or mouse) was thought to arise spontaneously and continually from nonliving matter.
While the hypothetical process of spontaneous generation was disproved as early as the 17th century and decisively rejected in the 19th century, abiogenesis has been neither proved nor disproved.
Who proposed the Theory of Abiogenesis?
By the late 19th century, English biologist Thomas Henry Huxley (1825–1895) coined the term abiogenesis to describe life forms emerging from non-living chemical systems. On first hearing the term, it may sound as if abiogenesis is merely a more modern take on spontaneous generation, but there is a major difference.
With spontaneous generation, the idea was that certain materials, be it meat, grain, or mud, were capable of constantly producing some kind of creature. What Huxley had in mind was the chemical reactions of life slowly emerging on the early Earth over a long period of time.
Huxley knew that the mixture would have to be more complex than Darwin’s ammonia and phosphoric salts, but he did not attempt to work out the details. Somehow, though, he thought an optimal mixture of simple chemicals generated the complex chemicals needed for life, such as enzymes, and the earliest living cells.
Evidences of Abigenesis Theory
The earliest physical evidence so far found consists of microfossils in the Nuvvuagittuq Greenstone Belt of Northern Quebec, in banded iron formation rocks at least 3.77 and possibly 4.28 Gya. This finding suggested life developed very soon after oceans formed.
Spontaneous generation was an early model for abiogenesis developed by Aristotle (384-322 BCE) which said that flies formed directly from decaying material and logs gave rise to crocodiles. Experiments by Louis Pasteur in the mid-1800s disproved spontaneous generation.
Since that time, scientists have been working to describe more probable models of abiogenesis which could explain the formation of life on Earth over 3.5 billion years ago.
Alexander Oparin and J.B.S. Haldane were the first scientists to independently propose a chemical-based theory for the evolution of life in the 1920s. They both hypothesized that Earth’s early atmosphere had mostly ammonia, water, hydrogen sulfide, carbon dioxide or carbon monoxide and phosphate, and very little oxygen and ozone.
Chemically, this means the atmosphere was reducing, capable of accepting electrons and forming new molecules. Under these primitive conditions, they thought, the effect of energy sources such as lightning, ultraviolet radiation, or even the shock from an impact could form organic molecules like amino acids. Oparin and Haldane’s theory is also known as the Primordial Soup theory.
The Primordial Soup theory goes on to propose that these organic molecules may have concentrated in certain locations like thermal vents in the ocean or shorelines and underwent a further transformation to more complex organic molecules, eventually resulting in life. The work of Oparin and Haldane laid the foundation for other scientists to create laboratory experiments to test these hypotheses.
The Miller-Urey Experiment
In 1953, chemists Harold Urey and Stanley Miller designed an experimental apparatus that duplicated the atmospheric conditions on Earth proposed by Oparin and Haldane. Urey and Miller filled a chamber with warm water, water vapor, methane, ammonia, and molecular hydrogen and then introduced pulses of electrical sparks into the chamber.
After one week, they analyzed the material in the chamber and found a variety of organic molecules including amino acids, verifying this aspect of the Primordial Soup theory.
The current research and debate about abiogenesis now center around how and why organic molecules may have accumulated in certain areas on the early Earth and how these molecules increased in complexity and eventually became self-replicating life.
Astrobiology, the scientific field that looks for extraterrestrial life, has provided additional information that supports abiogenesis. For example, studies on Saturn’s moon Titan have shown that its’ atmosphere has no oxygen and that there are organic molecules present.