A section of experts are important linkages between geological processes and biological processes and in this intersection Geobiology develops. An example is found in one of my favorite books: " Life as a geological force " (Life as a geological force), the Dutch geologist Peter Westbroek. Another example
summarized here is an interesting article Minik Rosing and co " The rise of continents: an essay on the geologic Consequences of photosynthesis " (The formation of the continents: an essay on the geological consequences of photosynthesis) published in 2006 in the prestigious journal Palaeogeography, Palaeoclimatology , Palaeoecology . Rosing and co
believe granite formation and subsequent stabilization of the continents due to the action of photosynthetic organisms . This idea comes from geological data: the geological record of rocks and fossils chemical begins 3,800 million years ago, coinciding with the first appearance signs of living organisms (detected through isotope 13 C in sedimentary remains of graphite).
From the beginning 4,600 million years ago, Earth had not built any stable solid structure at 800 m, only oceans and lithosphere viscous fluids. After this long period, the continents began to form from granite, a rock that is not recorded in any other planet (as opposed to the ubiquitous basalt on other planetary bodies). The granite is lighter and thermodynamically incompatible with basalt. To form granite, not enough to melt mantle rocks and add water: requires altering the composition of the magma enriched in silica, potassium, aluminum and other elements, which requires pre-altered basalt melt in the ocean. And the oceanic alteration could be favored by photosynthetic organisms.
To support his hypothesis, these authors calculated the thermal and chemical energy needed to maintain the carbon cycle on Earth, which is the basis of the metabolism of the biosphere, climate and the rock cycle through spoilage and weathering. Surprisingly, the chemical energy produced by photosynthesis is 3 times that of Earth's internal energy from the decomposition of radioactive elements and the residual heat caused by planetary accretion. The internal energy of the Earth is ridiculously low (much less than the 87 mW/m2 current average heat flux on the surface) compared with that obtained from the solar energy reaching the earth's surface (340 W/m2) caught through photosynthesis, with a primary production equivalent to 268 mW/m2.
Therefore, the contribution to the energy cycle chemoautotrophic organisms (those living on mineral oxides), is minimal in contrast to that of photosynthetic organisms. The first advantage of the existing chemical gradients in minerals, while photoautotrophs build new and much higher chemical gradients from light energy. Therefore they are able to build an atmosphere and hydrosphere in strong chemical imbalance, can alter the rocks very quickly and efficiently.
These data have important implications for astrobiology and space exploration. Rosing and co-authors say " In a world of purely chemoautotrophic primary production, burial of organic matter would leave no isotopic signal in sediments, and there would be no significant biological effect on the global carbon cycle in the absence of photosynthesis " . "The granitic continents are biomarkers of photosynthetic life probably in silicate planets in general. " "The terrestrial planets ... share similar characteristics of distribution of elements. The abundance of heat producing elements in relation to carbon thus provides insufficient energy to sustain a biosphere that can significantly influence the carbon cycle of any terrestrial planet that is not photosynthetic organisms. This should be borne in mind when shopping for buried traces of a biosphere on Mars. Such biosphere would probably global geochemical fingerprints, and would only be successful if to find members of a widely dispersed biosphere in a particular sample. "
0 comments:
Post a Comment