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SPLATS about the origins and history of life
The principles of the origins and history of life
- One theory of the origins of life with no evidence is panspermia. It is an interesting idea, but unsupported by any fossil or other evidence so far.
- Panspermia is based on the belief that our planet was somehow seeded with primitive life forms that were floating around in space, and managed to reach here.
- The main argument in favour of panspermia is that life seems to have appeared on Earth very soon after the earliest date at which it was possible for it.
- Around 1630, Jan Baptista van Helmont offered a recipe for making mice by spontaneous generation by leaving wheat and an old shirt, soaked in sweat for 21 days.
- In 1651 William Harvey published his Exercitationes de Generatione Animalium with the aphorism "ex ovo omnia", (all come from eggs), on the title page.
- The 1748 experiments of Buffon with John Needham seemed to show that micro-organisms could spring up spontaneously in jars of sterilized meat broth and gravy.
- In 1862, Louis Pasteur conclusively disproved that spontaneous generation of living organisms ever happens with a series of carefully controlled experiments.
- The history of life can be deduced from the evidence, which includes many other observations other than the fossil evidence, though that gives us a clear story.
- Before they could move onto the land, animals needed to have a way of breathing air, because gills do not work out of water, thanks to surface tension effects.
- Surface tension makes external gills almost useless in land animals, because the individual 'fibres' will become matted together. Lungs are needed instead.
- Serial endosymbiosis theory says the various parts of eucaryotic cells were once separate organisms which came together to form a more effective combination.
- In 1971, Lynn Margulis proposed an endosymbiont theory, otherwise known as serial endosymbiosis theory, to explain the origins of eucaryotic organelles.
- In 1977, researchers discovered chemosynthetically based communities located submarine thermal springs on the Galápagos Rift. Many others have since been found.
- Temperature affects many animals, although some living things are extremophiles and flourish in extremely high temperatures in volcanic and thermal springs.
- Life began early in the Precambrian era, probably at least 3800 million years ago: most of the rocks of that time have been lost or altered since then.
- Urey and Miller sparked a mixture of gases: ammonia, methane and steam, similar to what they thought might have been the atmosphere on the early Earth.
- Urey and Miller wanted to see if complex organic molecules can form, free of any living influence. The electrical sparks produced a complicated organic 'soup'.
- We suspect now that methane was absent from the original atmosphere, and that carbon was present as CO2. This means that the experiment probably proves nothing.
- Life forms changed very fast after the Cambrian explosion, for reasons which are still not completely clear, but probably relating to increased competition.
- One plausible explanation for the Cambrian explosion is that the evolution of vision forced animals to develop better ways of avoiding or resisting predators.
- Life evolved in the water, then came on to land: first plants, then the amphibians, or maybe the insects: the fossil evidence will probably never tell us which.
- Before they could grow to any height on the land, plants needed to have conductive tissues to carry water up to their tops, and special structural tissues.
This file is http://members.ozemail.com.au/~macinnis/scifun/splatslifeorig.htm, first created on February 19, 2008. Last recorded revision (well I get lazy and forget sometimes!) was on February 19, 2008.
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