From Allano, our geologist friend in Australia.
Sir Isaac Newton (1642-1726) was a famous scientist who was inspired by gravity. When sitting in his garden he saw an apple fall from a tree. He used logical thinking to explain gravity, and used logic in his extensive researches in mathematics, optics, astronomy and alchemy. You too can do the same to determine the origin of petroleum. You need a pleasant setting. Then ask yourself the right questions and give the best answers.
I suggest a nice place and a bottle of red, perhaps a Merlot from De Bortoli’s vineyard, which I often do when trying to make sense of the Murray Darling Basin Plan. Now the first question:
What is petroleum? Simplified, ideally it is a liquid mixture of hydrocarbons. Perhaps best represented by a range of alkanes, from methane CH4, thru hexane C6H8 (gasoline) to and beyond C16H34 (fuel oil). Petroleum is the most common liquid after water to be found on the Earth, so it must be made from, or originate from common materials.
Question two: What are they, these materials, that react to form a hydrocarbon? The hydrogen source is easy…it’s water, or to be more precise, sea water, which also contains salt, NaCl, which acts as a catalyst to make reactions go better.
The carbon source is more variable… it is likely to be a carbonate rock, such as limestone, marble, chalk CaCO3, or dolomite CaMg(CO3)2, or even magnesite MgCO3. Let’s first consider marble, composed of CaCO3, which may originally have been limestone derived from shells, or else be like dolomite and be a chemical precipitate in Nature. It doesn’t really matter.
So we have CaCO3 + 2H2O = CH4 methane + CaO + 5O so we need a reducing agent, which is most likely iron or ferrous iron from olivine FeSiO4, next we add some silica or quartz to give:
CaMg(CO3)2 marble or dolomite + 5Fe + xSiO2 + 4H2O = 2CH4 methane + x(CaMgFe)SiO3 pyroxene
So we have represented marble or dolomite plus quartz and water mixture being converted to petroleum and a pyroxene mineral of sorts.
Next question: Where could this happen? Considering plate tectonics, my prediction is that in the subduction zone where crustal material is dragged down under the adjacent continental plate by convection currents in the mantle……everything in the crust, sea water, sediments, including coal measures and the kitchen sink, goes down to a melting zone in the upper mantle of the Earth, and here petroleum is formed…. I surmise. Once formed it migrates upwards along fault zones to be trapped, and accumulate in sedimentary rocks layered above where it is recovered by drilling.
That, more or less, is the abiotic theory of origin for petroleum. It means that petroleum is continuously being formed at high temperatures and pressures in the upper mantle of the Earth. Today there are hotspots where this seems to be occurring, such as at active plate boundaries, like in Indonesia, Venezuela, and along the Andes, and cool or cold spots where it has occurred in the past and oil fields are present. The Russians pioneered the Abiotic Theory and have applied it successfully to show where to prospect for oil.
When I was a geology student (ca 1955) the “Theory of Plate Tectonics” was not known. I remember writing an assignment about Continental Drift, but no one knew how or why it occurred, or knew that the Atlantic Ocean was splitting down the middle and the continents either side were moving apart. So the Theory of Plate Tectonics and its moving continents is now fully accepted by geologists, but little known by the general public, and least of all by politicians, who seem overwhelmed and confused by even climate change, which is one of the long term consequences of moving continents. Hydrocarbons do occur in other parts of our galaxy. NASA reports on seas of liquid methane and ethane on Saturn’s moon, Titan, so the climate is very cold there. Time for another vino.
Allan Taylor, habitat21
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