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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| Panspermia | 2/5 | https://en.wikipedia.org/wiki/Panspermia | reference | science, encyclopedia | 2026-05-05T03:37:50.050920+00:00 | kb-cron |
== History == Panspermia has a history dating back to the 5th century BCE and the natural philosopher Anaxagoras. Classicists came to agree that Anaxagoras maintained the Universe (or Cosmos) was full of life, and that life on Earth started from the fall of these extra-terrestrial seeds. Panspermia as it is known today, however, is not identical to this original theory. The name, as applied to this theory, was only first coined in 1908 by Svante Arrhenius, a Swedish scientist. Prior to this, since around the 1860s, many prominent scientists were becoming interested in the theory. More recent advocates include Sir Fred Hoyle and Chandra Wickramasinghe. In the 1860s, there were three scientific developments that began to bring the focus of the scientific community to the problem of the origin of life. Firstly, the Kant-Laplace Nebular theory of solar system and planetary formation was gaining favor, and implied that when the Earth first formed, the surface conditions would have been inhospitable to life as we know it. This meant that life must have arisen on Earth at a later date, without biological precursors. Secondly, Charles Darwin's famous theory of evolution implied some elusive origin, because in order for something to evolve, it must start somewhere. In his Origin of Species, Darwin was unable or unwilling to touch on this issue. Third and finally, Louis Pasteur and John Tyndall experimentally disproved the (now superseded) theory of spontaneous generation, which suggested that life was constantly arising from non-living matter and did not have a common ancestor, as suggested by Darwin's theory of evolution. Altogether, these three developments in science presented the wider scientific community with a seemingly paradoxical situation regarding the origin of life: life must have arisen from non-biological precursors after the Earth was formed, and yet spontaneous generation as a theory had been experimentally disproved. From here is where the study of the origin of life branched. Those who accepted Pasteur's rejection of spontaneous generation began to develop the theory that under (unknown) conditions on a primitive Earth, life must have arisen from non-living material. This theory became known as abiogenesis, and is the currently accepted one. On the other side of this are those scientists of the time who rejected Pasteur's results and instead supported the idea that life on Earth came from existing life. This necessarily requires that life has always existed somewhere on some planet, and that it has a mechanism of transferring between planets. Thus, the modern treatment of panspermia began in earnest. Lord Kelvin, in a presentation to The British Association for the Advancement of Science in 1871, proposed the idea that similarly to how seeds can be transferred through the air by winds, so can life be brought to Earth by the infall of a life-bearing meteorite. He further proposed the idea that life can only come from life, and that this principle is invariant under philosophical uniformitarianism, similar to how matter can neither be created nor destroyed. There would have always been planets spreading life throughout the universe because, he said, "we all confidently believe that there are at present, and have been from time immemorial, many worlds of life besides our own." This argument was heavily criticized because of its boldness, and additionally due to technical objections from the wider community. In particular, Johann Zollner from Germany argued against Kelvin by saying that organisms carried in meteorites to Earth would not survive the descent through the atmosphere due to friction heating. The arguments went back and forth until Svante Arrhenius gave the theory its modern treatment and designation. Arrhenius argued against abiogenesis on the basis that it had no experimental foundation at the time, and believed that life had always existed somewhere in the Universe, arguing that "we may become accustomed to the idea that life is eternal, and hence that it is useless to inquire into its origin." He focused his efforts of developing the mechanism(s) by which this pervasive life may be transferred through the Universe. At this time, it was recently discovered that solar radiation can exert pressure, and thus force, on matter. Arrhenius thus concluded that it is possible that very small organisms such as bacterial spores could be moved around due to this radiation pressure. At this point, panspermia as a theory now had a potentially viable transport mechanism, as well as a vehicle for carrying life from planet to planet. The theory still faced criticism mostly due to doubts about how long spores would actually survive under the conditions of their transport from one planet, through space, to another. Despite all the emphasis placed on trying to establish the scientific legitimacy of this theory, it still lacked testability; that was and still is a serious problem the theory has yet to overcome. Furthermore, as Dennis Danielson and Christopher M. Graney have pointed out, the theory is essentially based on the idea of an eternal, unchanging universe with no beginning and in which life is eternal, and not an evolving "Big Bang" universe. Support for the theory persisted, however, with Fred Hoyle (famous for his opposition to the Big Bang Theory and for promoting his theory of an unchanging, "steady-state" universe) and Chandra Wickramasinghe using two reasons for why an extra-terrestrial origin of life might be preferred. First is that required conditions for the origin of life may have been more favorable somewhere other than Earth, and second that life on Earth exhibits properties that are not accounted for by assuming an endogenic origin. Hoyle studied spectra of interstellar dust, and came to the conclusion that space contained large amounts of organics, which he suggested were the building blocks of the more complex chemical structures. Critically, Hoyle argued that this chemical evolution was unlikely to have taken place on a prebiotic Earth, and instead the most likely candidate is a comet. Furthermore, Hoyle and Wickramasinghe concluded that the evolution of life requires a large increase in genetic information and diversity, which might have resulted from the influx of viral material from space via comets. Hoyle reported (in a lecture at Oxford on January 16, 1978) a pattern of coincidence between the arrival of major epidemics and the occasions of close encounters with comets, which lead Hoyle to suggest that the epidemics were a direct result of material raining down from these comets. This claim in particular garnered criticism from biologists. Since the 1970s, a new era of planetary exploration meant that data could be used to test panspermia and potentially transform it from conjecture to a testable theory. Though it has yet to be tested, panspermia is still explored today in some mathematical treatments, and as its long history suggests, the appeal of the theory has stood the test of time.