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A second group of sulphur-processing bacteria can convert this sulphur and sulphide back into sulphate, using oxygen as the electron acceptor. These sulphide-and sulphur-oxidizing bacteria may occur as biofilms above the sulphate-reducing zone. They also bloom copiously around hot, sulphide-rich submarine vents known as 'black smokers', where they play an important role in the food chain of the vent community. Their metabolism results in further 34S depletion of the sulphur isotopes (to - 60 ), which can be measured in the fossil record.
As an ocean basin continues to grow, contemporaneous mineralization takes place at the mid-ocean ridge, and has been observed at certain locations along the Pacific (Corliss et al., 1979), Atlantic (Scott et al., 1973), and Indian Ocean ridges. The mineralization is of hydrothermal origin and its location depends upon the availability of oceanic crust of high permeability overlying the magma chamber which allows fluids to percolate with relative ease. Hydrothermal processes of low intensity lead to the formation of ferromanganese nodules, and encrustations of iron and manganese on pillow basalts at the layer 1-layer 2 interface. Higher intensity hydrothermal activity has been observed at some locations, such as on the East Pacific Rise where discharge is of two types. Black smokers are vents where pyrrhotite particles are discharged, producing ores which may be zinc- or iron-rich and containing lesser amounts of cobalt, lead, silver, and cadmium. At white smokers little sulfide...
In a recent twist to the classic Oparin-Haldane biochemical model, Euan Nisbet (University of London) and Norman Sleep (Stanford University) proposed the hydrothermal model for the origin of life in 2001. In this model, the ancestor of all living things was a hyperthermophile, a simple organism that lived in unusually hot conditions. The transition from isolated amino acids to DNA may then have happened in a hot-water system associated with active volcanoes, rather than in some primeval soup at the ocean e surface. There are two main kinds of hot-water systems on Earth J today, 'black smokers' found in the deep oceans above mid-ocean f ridges where magma meets sea water, and hot pools and fumaroles e fed by rainwater that are found around active volcanoes.
Reasoning forward is much more problematic. Although we can imagine many possible mangers for the birth of life - deep smokers in the abyssal depths, tidal pools, hot springs, and many others - and although each could plausibly produce primitive precursors to many of the reactions that now constitute cellular metabolism, we have (in my opinion) no idea how these simple reactions might have blundered together to make the first protocell. Monkeys sitting at typewriters pecking out Shakespeare seems child's play by comparison. For example, we still do not know If, in time, we cannot trace such a path, what then In science, until it has been proven that something cannot be done, it is always possible that it can be done. Proving that life did not originate by accident in tidal pools or black smokers will be more difficult than proving that it might have done so. Also, patience may be in order. What is impossible for science today may be trivial for science in the future.
As the Earth's surface cooled, the lithosphere, its rocky crust, began to differentiate as a cooler upper layer above the underlying asthenosphere. As the rocky lithosphere formed, magma convection became restricted to the asthenosphere, and the upper crust formed plates that were moved by mantle convection. This marks the beginning of plate tectonics (see p. 42). Heat loss from the Earth now happened mainly round the margins of these early plates, and black smokers, associated with hydrothermal activity, began to form.
The notion that pyrite (and other metal sulphides, especially nickel) could play the key role in the initiation of life has attracted attention for another potentially important reason. This is because such sulphides are abundant in hydrothermal systems, most famously in the form of the 'black smokers' found on oceanic spreading ridges. As potential sites for the origin of life, these systems are attractive for several reasons. These include their dynamic nature with strong temperature gradients, the possibility of active mineral growth, and a strong flux of both heated water and various chemicals. Such settings are now the focus of investigations into various prebiotic syntheses that might be alternative sources for some of the major building blocks of life.46 Hydrothermal systems have another advantage in that, of all the regions of the early Earth, they would have been the most immune to the searingly powerful destructive forces released by a series of violent impacts early in the...
Large, diverse communities of previously unknown organisms crowd the hot, nutrient-rich waters surrounding black smokers, volcanic vents on the bottom of the sea. The denizens of these recently discovered ecosystems include sulfur-eating shrimp and giant tube worms up to ten feet long. As weird and unearthly as these deep-ocean communities seem to us, many scientists are starting to think that our most distant ancestors came from just such a place.
The hydrothermal model is a recently proposed modification to the Oparin-Haldane biochemical model (Nisbet & Sleep 2001). According to this view, the last universal common ancestor of life (sometimes abbreviated as LUCA) was a hyperthermophile, a simple organism that lived in unusually hot conditions. The transition from isolated amino acids to DNA (Fig. 8.1) may then have happened in a hot-water system associated with active volcanoes. There are two main kinds of hot-water systems on Earth today, hot pools and fumaroles fed by rainwater that are found around active volcanoes, and black smokers in the deep ocean. Black smokers arise along mid-ocean ridges, where new crust is being formed from magma welling up as major oceanic plates move apart (see p. 42). Seawa-ter leaks down into the crust carrying sulfur as sulfate, mixes with molten magma and emerges as superheated steam, with the sulfur now concentrated as sulfide. As minerals precipitate in the cooler sea bottom waters, they...
The solar energy captured by chloroplasts in plants lies at the base of complicated food chains, in which the energy passes from plants through herbivores, which may be insects, through carnivores, which may be insects or insectivores as well as wolves and leopards, through scavengers such as vultures and dung beetles, and eventually to agents of decay such as fungi and bacteria. At every stage of these food chains, some of the energy is wasted as heat as it passes through, while some of it is used to drive biological processes such as muscle contraction. No new energy is added after the initial input from the sun. With a few interesting but minor exceptions such as the denizens of deep ocean 'smokers' whose energy comes from volcanic sources, all the energy that drives life comes ultimately from sunlight, trapped by plants.
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