Darwin guessed life began in a warm little pond
In a letter to Joseph Hooker on 1 February 1871, Charles Darwin speculated that life's first spark might have struck in a warm little pond rich in ammonia and phosphoric salts, with light, heat and electricity on hand. He also saw why it couldn't happen again: any such chemistry today would be eaten at once.
Abiogenesis is the study of how living things arose from non-living chemistry. Nobody has watched it happen in a laboratory, and scientists doubt it was a single event. The leading view is a gradual climb in complexity: a habitable planet, the formation of organic molecules, molecules that copy themselves, self-assembling membranes and self-sustaining chemical cycles. Any full account must explain the four chemical families life depends on: fats for membranes, sugars for energy and structure, amino acids for proteins, and the nucleic acids DNA and RNA for heredity.
The central puzzle is a chicken-and-egg loop. Cells copy DNA using an enzyme, DNA polymerase, whose recipe is itself written in DNA, so neither can be made without the other. One popular escape route is an RNA world, in which RNA both stored information and catalysed reactions. Rival metabolism-first ideas argue that chemistry on early Earth produced the building blocks before any replicator appeared.
Experiments have chipped away at the problem. In 1924 Alexander Oparin, and in 1929 J. B. S. Haldane, proposed that the first cells organised themselves in a primordial soup. In 1952 Stanley Miller and Harold Urey showed that amino acids can form from simple inorganic compounds under conditions like those of early Earth, and amino acids have since turned up in meteorites, comets and star-forming clouds. Earlier, spontaneous generation, the belief traced to Aristotle that insects sprang from rotting matter, had fallen after Francesco Redi showed in 1668 that meat kept from flies grew no maggots.
Timing suggests life was quick off the mark. Earth formed about 4.54 billion years ago, and the earliest evidence of life, from Western Australia, dates to about 3.8 billion. Studying genes shared by bacteria and archaea points to a last universal common ancestor with hundreds of genes, living without oxygen, possibly near deep-sea hydrothermal vents.
Source: Abiogenesis
