Geomicrobiology

Geomicrobiology ( ancient Greek γῆ, ge " earth ", μικρός, micros "small", βίος, bios, " life" and λόγος, logos, " word" ) is a branch of microbiology. It deals mainly with the effects of microbial metabolic processes on the nature of the near-surface layers of the earth ( earth's crust and lithosphere, hydrosphere and atmosphere) and with the properties of the respective microorganisms. Both the current influences as well as the history of the earth are treated.

Special Significance of Microorganisms for the geochemistry

The influence of microorganisms on the state of the earth's surface, both in quantitative and in qualitative terms, of particular importance. This is due to the following features of the microorganisms against larger creatures:

According to estimates by the mass of microorganisms is about as large or even larger than that of all other living beings.
Since microorganisms because of their small size have a large specific surface area (based on their mass) and the metabolic rate of organisms is greater, the larger the specific surface area is micro-organisms are characterized by a specific, related to their mass metabolic rate that is orders of magnitude higher than those of larger organisms. The large biomass of microorganisms on the earth and the high specific metabolic rate is the reasons why the metabolic processes of micro-organisms are of particular importance for the quantitative geochemical properties of the earth's surface.
Microorganisms are characterized by a greater qualitative diversity of metabolism than larger creatures: they cause many chemical reactions to which other creatures are not capable, for example, formation of methane and hydrogen sulfide, the oxidation of ammonia and hydrogen sulfide.
Some microorganisms, especially bacteria, to extreme environmental conditions adapted (so-called " extremophiles "). They can grow for example in strongly acidic or alkaline conditions (pH 1, 11 ) or at temperatures up to 120 ° C or 4 ° C or at pressures above 1000 bar ( 100 MPa).

Geochemical significant microbial nutrient cycling

Below are some examples of microbial conversion processes are listed that are for the geochemistry of the near-surface layers of the earth are of particular importance:

Consumption of carbon dioxide (CO2 ) for the formation of biomass ( CO2 assimilation ). The result is due to a lowering of CO2 concentration in waters and in the atmosphere alkalinization (increase the pH ) of water bodies and precipitation of calcium carbonate ( CaCO3) and the formation of limestone.
Incorporation of calcium carbonate ( CaCO3) in skeletons (especially in coccolithophores and foraminifera ) and thus formation of calcareous rocks.
Incorporation of silica (SiO2) in skeletons (especially diatoms and radiolarians ) and thus formation of SiO2 rocks after diagenesis as chert.
Formation of methane (CH4 ) ( methanogenic archaea by ), which acts as a " greenhouse gas ".
Oxidation of ferrous iron ( Fe2 ) and thus immobilization of iron compounds in the form of trivalent iron.
Reduction of trivalent iron and hence mobilization of iron from substantially water-insoluble compounds in the form of Fe2 ions.
Oxidation of hydrogen sulfide (H2S) and elemental sulfur to sulfuric acid and thus acidification of the environment
To trivalent dissolution of heavy metal sulfides (eg, pyrite and marcasite, both FeS2 ) by abiotic oxidation of sulfide by ions of trivalent iron and biotic oxidation of the elemental sulfur thus formed and the sulfur compounds formed and biotic re-oxidation of divalent iron ions; Sequence of operations is the dissolution of the sulfide minerals, and mobilization of the heavy metals.
Reduction of sulphate to hydrogen sulphide (H2S) with sulphate-reducing bacteria, with the result that the heavy metals are precipitated as substantially water-insoluble sulphides, and thus immobilized.

Microorganisms and geochemical evolution on Earth

Microorganisms colonize the earth for at least 3.8 billion years, larger, multicellular creatures, however, only since about 0.7 billion years ago. Microorganisms have influenced very early by their metabolism the geochemical evolution of the near-surface layers of the earth ( earth's crust and lithosphere, hydrosphere and atmosphere):

Drastic reduction of the content of carbon dioxide (CO2 ) which at the beginning was the main constituent of the atmosphere, and therefore, was also included in the hydrosphere in high concentration by means of CO2 assimilation ( bond of carbon in biomass). This alkalization of the oceans, precipitation of carbonates and formation of calcareous rocks.
Form at the beginning only in very low concentrations present elemental oxygen (O2, dioxygen ) by oxygenic photosynthesis. This drastic changes in hydro-and lithosphere and implications for the evolution of living beings arose.
Immobilization of the beginning in the seas as Fe2 ions dissolved divalent iron by oxidation to ferric iron, which was precipitated in the form of Fe ( III ) compounds and ultimately into hematite (Fe2O3 ) was transferred ( formation of " banded iron stones " " Bändererz " english "Banded Iron Formations " = " BIF " and Rotsandsteinen, " Red Bed ").
Formation of water- soluble sulfates difficult as calcium sulfates (gypsum, anhydrite ) and barium sulphate (barytes ).