Life On Earth Could Have Gotten Its Start In Primordial Mud
Although they have not proved Genesis (2:7), that "God formed man of dust from the ground, and breathed into his nostrils the breath of life, and man became a living creature," researchers at Cornell say they've shown clay to be a strong candidate for having swaddled the first ingredients of life well enough to make more advanced life possible.
"Many different environments have been considered for this pre-cellular evolutionary stage," wrote Dan Luo, professor of biological and environmental engineering and a member of the Kavli Institute at Cornell for Nanoscale Science at Cornell University in the Nov. 7 online issue of the journal Scientific Reports. And clay is one of them.
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Clay first formed from silicates leached from rocks - just around the same time biomolecules began to form into proto-cells - the precursors of cells, - and eventually membrane-enclosed cells. Over time, chemicals confined in those spaces could have carried out the complex reactions that formed proteins, and even DNA. Luo's team thought clay hydrogels -- sponge-like masses of microscopic spaces -- could have confined and protected those chemical processes until the membrane that surrounds living cells developed.
Luo and his team tested this hypothesis by placing clay in simulated ancient seawater. Earlier experiments have shown that amino acids and other biomolecules could have been formed in primordial oceans, drawing energy from lightning or volcanic vents. "In defining the pre-cellular environment," Luo wrote, "it is important to address how did biomolecules encounter each other and maintain sufficient proximity to perform complicated biochemical reactions?" And, without the protective layer of a cell membrane, what protected them from the harshness of that ocean?
By suspending clay minerals in vats of imitation ocean water, Luo showed that a sponge-like muddy material forms, replete with hydrogels, or microscopic holes, that are perfect for swaddling the chemicals that could have formed the precursors of life.
"We discovered that clay forms a hydrogel in ocean water," Luo said. "This is important because clay and ocean water coexisted on and dominated the early Earth surface." After mixing clay with ocean water in a 1:1 ratio, clay spontaneously and instantaneously formed a bulk hydrogel. Clay hydrogel also formed even in a larger reservoir of ocean water, in a 106:1 ratio of ocean water to clay, "more realistic to the scenario on early Earth." The bulk-scale clay hydrogel was easily broken down by shear forces into micro-particles, which acted as the confinement for biomolecules and biochemical reactions.
The researchers demonstrated that a clay hydrogel could adequately protect its contents of bio-chemicals and even DNA from damaging enzymes, or "nucleases." Bio-molecules attach easily to the surface of clay. They also noted that cytoplasm - the interior environment of a cell - behaves much like a hydrogel.
How these bio-molecules evolved remains to be explained, Luo said. For now, his research group is working to understand why a clay hydrogel works so well, with an eye to practical applications in cell-free protein production.
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