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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Earliest known life forms | 3/3 | https://en.wikipedia.org/wiki/Earliest_known_life_forms | reference | science, encyclopedia | 2026-05-05T07:15:42.867278+00:00 | kb-cron |
While current geochemical evidence dates the origin of life to possibly as early as 4.1 Ga, and fossil evidence shows life at 3.5 Ga, some researchers speculate that life may have started nearly 4.5 billion years ago. According to biologist Stephen Blair Hedges, "If life arose relatively quickly on Earth ... then it could be common in the universe." The possibility that terrestrial life forms may have been seeded from outer space has been considered. In January 2018, a study found that 4.5 billion-year-old meteorites found on Earth contained liquid water along with prebiotic complex organic substances that may be ingredients for life.
=== Hydrothermal vents === Hydrothermal vents have long been hypothesized to be the grounds from which life originated. The properties of ancient hydrothermal vents, such as the geochemistry, pressure, and temperatures, have the potential to create organic molecules from inorganic molecules. In experiments performed by NASA, it was shown that the organic compounds formate and methane could be created from inorganics in the conditions of ancient hydrothermal vents. The production of organic molecules could have led to the formation of more complex organic molecules, such as amino acids that can eventually form RNA or DNA.
=== Darwin's hypothesis === Charles Darwin is well-known for his theory of evolution via natural selection. His theory for the origin of life was a "warm little pond" that harbored necessary elements for the creation of life such as "ammonia and phosphoric salts, lights, heat, electricity ... so that a protein compound was chemically formed ready to undergo still more complex changes." However, he mentioned that such an environment today would likely have been destroyed faster than it would take to form life. With this, Darwin's ideas are generally regarded as the spontaneous generation hypothesis.
=== Oparin–Haldane hypothesis === In 1924, Alexander Oparin suggested that the early atmosphere on Earth was full of reducing components such as ammonia, methane, water vapor, and hydrogen gas. This was proposed after atmospheric methane was discovered on other planets. Later, in 1929, J. B. S. Haldane published an article that proposed the same conditions for early life on Earth as Oparin suggested. Their hypothesis was later supported by the Miller–Urey experiment.
=== Miller–Urey experiment ===
At the University of Chicago in 1953, a graduate student named Stanley Miller carried out an experiment under his professor, Harold Urey. The method would allow for reducing gases to simulate the atmosphere early on Earth and a spark to simulate lightning. There was a reflux apparatus that would heat water and mix into the atmosphere where it would then cool and run into the "primordial ocean". The gases that were used to mimic the reducing atmosphere were methane, ammonia, water vapor, and hydrogen gas. Within a day of allowing the apparatus to run, the experiment yielded a "brown sludge" which was later tested and found to include the following amino acids: glycine, alanine, aspartic acid, and aminobutyric acid. In the following years, many scientists attempted to replicate the results of the experiment, which is now known as a fundamental approach to the study of abiogenesis. The Miller–Urey experiment was able to simulate the early conditions of Earth's atmosphere and produced essential amino acids that likely contributed to the production of life.
=== Clay hypothesis === Cairns-Smith first introduced this hypothesis in 1966, where they proposed that any crystallization process is likely to involve a basic biological evolution. Hartman then added on to this hypothesis by proposing in 1975 that metabolism could have developed from a simple environment such as clays. Clays have the ability to synthesize monomers such as amino acids, nucleotides, and other building blocks and polymerize them to create macromolecules. This makes it possible for nucleic acids like RNA or DNA to be created from clay, and cells could further evolve from there.
== Gallery ==
== See also ==
== References ==
== External links == Vitae (BioLib) Biota (Taxonomicon) Life (Systema Naturae 2000) Wikispecies — a free directory of life Life in the Universe — Stephen Hawking (1996) Video (24:32): "Migration of Life in the Universe" on YouTube — Gary Ruvkun, 2019.