|What can deep time teach us ?|
Whilst doing a little background research into biological routes to hydrogen production, I came across a scientific journal paper, I can’t recall which, that suggested that the geological evidence indicates that Earth’s second atmosphere not only had a high concentration of methane, but also high levels of hydrogen gas.
Previously, my understanding was that the development of microbiological life included a good number of methanogens (micro-life that produces methane as a waste product) and methanotrophs (those that “trough” on methane), but that hydrogenogen (“respiring” hydrogen gas) and hydrogenotroph (metabolising hydrogen) species were a minority, and that this was reflected in modern-day decomposition, such as the cultures used in biogas plants for anaerobic digestion.
If there were high densities of hydrogen cycle lifeforms in the early Earth, maybe there are remnants, descendants of this branch of the tree of life, optimal at producing hydrogen gas as a by-product, which could be employed for biohydrogen production, but which haven’t yet been scoped.
After all, it has only been very recently that psychrophiles have been added to the range of microorganisms that have been found useful in biogas production – cold-loving, permafrost-living bugs to complement the thermophile and mesophile species.
Since hydrogen and methane are both ideal gas fuels, for a variety of reasons, including gas storage, combustion profiles and simple chemistry, I decided I needed to learn a little more.
I have now read a plethora of new theories and several books about the formation of the Earth (and the Moon) in the Hadean Eon, the development of Earth’s atmosphere, the development of life in the Archaean Eon, and the evolution of life caused by climate change, and these developments in living beings causing climate change in their turn.
Most of this knowledge is mediated to us by geology, and geobiology. But right at its heart is catalytic chemistry, once again. Here’s Robert Hazen (Robert M. Hazen) from page 138 of “The Story of Earth” :-
“Amino acids, sugars, and the components of DNA and RNA adsorb onto all of Earth’s most common rock-forming minerals […] We concluded that wherever the prebiotic ocean contacted minerals, highly concentrated arrangements of life’s molecules are likely to have emerged from the formless broth […] Many other researchers have also settled on such a conclusion – indeed, more than a few prominent biologists have also gravitated to minerals, because origins-of-life scenarios that involve only oceans and atmosphere face insurmountable problems in accounting for efficient mechanisms of molecular selection and concentration. Solid minerals have an unmatched potential to select, concentrate, and organize molecules. So minerals much have played a central role in life’s origins. Biochemistry is complex, with interwoven cycles and networks of molecular reactions. For those intricately layered processes to work, molecules have to have just the right sizes and shapes. Molecular selection is the task of finding the best molecule for each biochemical job, and template-directed selection on mineral surfaces is now the leading candidate for how nature did it […] left- and right-handed molecules […] It turns out that life is incredibly picky : cells almost exclusively employ left-handed amino acids and right-handed sugars. Chirality matters […] Our recent experiments have explored the possibility that chiral mineral surfaces played the starring role in selecting handed molecules, and perhaps the origins of life as well. […] Our experiments showed that certain left-handed molecules can aggregate on one set of crystal surfaces, while the mirror image […] on other sets […] As handed molecules are separated and concentrated, each surface becomes a tiny experiment in molecular selection and organization. On its own, no such natural experiment with minerals and molecules is likely to have generated life. But take countless trillions of trillions of trillions of mineral surfaces, each bathed in molecule-rich organic broth […] The tiny fraction of all those molecular combinations that wound up displaying easier self-assembly, or developed a stronger binding to mineral surfaces […] survived […] possibly to learn new tricks.”