De los niños migrantes hacia su propio proceso de adaptación

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in a single teaspoon. Chemobacteria extremophiles that live deep in the earth only need water to live in and heat of the earth (energy) to reduce (or oxidize) rocks and minerals. Hydrogen (H₂) gas is released as water seeps through rock (produced from iron oxide reacting with water);

molecular hydrogen can be reacted with carbon (C), oxygen (O) or sulfur (S) to sustain deep-rock extremophile respiration. Another rock type, limestone extremophiles, chemically reduce the rock they live in with their very slow rates of metabolism, releasing carbon dioxide (CO₂) and forming caves. Sea-vent extremophiles draw thermal energy from below the ocean floor to make carbohydrates; these chemobacteria can create carbohydrates capturing close-by carbon in a chemosynthetic cousin of the carbon cycle.

For example, hot water gushing from deep-sea vents is laden with hydrogen-sulfur and hydrogen-iron compounds. Extremophiles near the vents combine these molecules with the carbon and oxygen molecules dissolved in sea water. These reactions form larger molecules, carbohydrates (from the H/O/C atoms).

Scientists believe life on earth may have begun in the ocean-bottom environment of a thermal vent (very hot—800°F, mineral rich, reducing environment). Life evolved. Photosynthetic blue-green “algae,” which are primitive bacteria (cyanobacteria), are still abundant today, made earth’s oxygen atmosphere and supercharged respiration 2.2bya (billion years ago). Today these cyanobacteria can be easily observed as thick mats covering the bottom in shallow waters (e.g. Oscillatoria). Cyanobacteria are the most abundant organisms in the ocean. Cyanobacteria have recently found in the most barren area of Antarctica, where no other life has been found; similar observations have been made in the high Arctic. They live just below the surface of rocks (within the rock-like chemosynthetic extremophiles). Cyanobacteria favor carbonate substrates, residing in limestone (CaCO₃) is a widespread pattern. Stromatolites are carbonate rock-dwelling cyanobacteria that make-up the oldest fossil structures, known as stromatoliths. Stromatoliths are large columnar, calcium carbonate rock-layered structures; some have been found to be up to 3.6 billion years old. These were originally formed largely through in-situ precipitation of layers (within the cyanobacterium) during Archean (2.5–3.6bya) and older Proterozoic (2.2–2.5bya) times; however, younger Proterozoic (0.55–1.0bya) stromatoliths grew largely through the accretion of carbonate sediments, enabled by an oxygenating environment.

Stromatoliths still exist today in environments salty enough to deter grazers from feeding upon them, such as those found in Australia’s shallow tidal flats or The Dead Sea. Complex organisms are relatively new on earth.

Sponges are a possible animal ancestor from over a billion years ago.

In Peter Ward and Donald Brownlee’s The Life and Death of Planet Earth, we learn that oxygen began accumulating in earth’s atmosphere

2.2bya (billion years ago). The arrival of free oxygen (O₂) changed the environment. The atmosphere and ocean turned blue in color, respectively changing a Mars-orange sky and vitriol-green sea. There may have been some kind of a bacterial mass extinction caused by this new toxic O₂ waste, but there may have been no extinction at all. A large die-back is not really an extinction; chemosynthetic bacteria still live in extremophile environments. Around rift zone sea vents, it is common to find enough free iron today to form significant quantities of black ferrous sulfide (FeS₂) from hydrogen sulfide (H₂S). Also, sulfate-reducing bacteria (sulfide-producing bacteria) thrive today in the black layer below moist soils, water-covered sediments and in black water columns containing hydrogen sulfide.

Above this sulfate-reducing layer is the omnipresent red-brown soil, or brown sediment layer, or water-column cloud of sulfate-fixing bacteria (where oxygen is available). Above this layer is the green soil, surface, or water column zone of photosynthesis that contains algae and/or photosynthetic bacteria.

Cyanobacteria survived the freezing of earth’s ocean surface when the world became a snowball, like Europa (Jupiter’s moon), 2.3bya. This snowball (worldwide glaciation) occurred as the oceans were losing their last iron salts (iron enhances photosynthesis). Atmospheric oxygen levels were near 1%. Prior to forming an atmosphere containing significant amounts of free oxygen, any available atmospheric oxygen (O₂) would have first oxidized atmospheric methane (CH₄), producing carbon dioxide (CO₂) and water (H₂O). Methane (CH₄) is a greenhouse gas, about 25 times (25×) as effective in this role as carbon dioxide (CO₂). Losing atmospheric methane (CH₄) would have had a chilling effect, even with earth’s originally-high atmospheric carbon dioxide levels. Back then, respiration was primarily anaerobic. There were at least two more snowballs (worldwide glaciations) between 580–750mya (million years ago), as photosynthesis from cyanobacteria once again decreased atmospheric greenhouse gas levels (cooling the surface). The snowball’s ice cover decreased photosynthesis and kept any CO₂ in the atmosphere, and that helped with warming and melting the snowball. Volcanic CO₂ may have helped reverse the more recent snowballs. The main source of volcanic CO₂ today is from extensive deposits of seabed limestone that are continually buried at the edges of continents, in tectonic plate subduction zones. As the limestone (CaCO₃) plunges deep into the earth, CO₂ is released and vented to the surface, often in violent eruptions. Upon eruption, volcanoes at first enhance global cooling; they also spill greenhouse gasses (water vapor + CO₂) into the atmosphere, eventually warming the surface. There wasn’t much seafloor limestone to do significant cooling or warming 2.3bya, and there was still far less than today’s limestone deposits back 580–750mya. (Super-continent Rodinia Beyond Ancient History 17

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formed 1.1bya and subsequently broke-up 750mya.) During the time following the more recent snowballs, oxygen (O₂) levels began to surpass the atmospheric levels of today (collagen needs O₂ and complex animal life needs collagen) , grazers of the seafloor shallow-water green mats arrived, along with predators, to off-gas CO₂ (from aerobic respiration) and help to prevent future snowball formation. Complex life became larger and more abundant. The conditions of life have been anything but constant, or similar to the conditions of our present time. In Peter Ward and Donald Brownlee’s The Life and Death of Planet Earth, we learn that the sun is getting hotter; it is 30% brighter today than it was 4.6bya. At the time of the first snowball (2.3bya), when the glaciers froze the oceans all the way to the equator, the sun’s intensity was 6% weaker than it is today.

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