In myths and origin stories around the world, various cultures and religions refer to clay as the vessel of life, the primary substance that the creator gods saturate with a self-sufficient existence. Nowadays we have biology to explain what life is like, but can these ancient tales hit the mark more often than we think?
In a paper written to commemorate the work of Ned Seaman, inventor of the field of DNA nanotechnology, UC Santa Barbara biophysicist Helen Hansma outlines her long-standing idea that: Primitive lifein the pre-cellular arrangements that evolved into fat and protein cells, may have started in the myxomas Clay. Her paper appears in Biophysical Journal.
Hansma’s hypothesis was originally proposed nearly 16 years ago, and joins many other speculations about how life on Earth first appeared. Among them are the well-known “RNA world,” where self-replicating RNA molecules evolved into DNA and proteins, and the concept of “metabolism first,” which says life evolved from spontaneous chemical reactions. There is also a “pizza” hypothesis that claims that life came from terrestrial organic biomolecules. Other hypotheses about clay say that life may have arisen on montmorillonite, or iron-rich clay.
Hansma didn’t set out to discover how life on Earth evolved when she first came up with her idea. Instead, as a biophysicist and program director at the National Science Foundation around 2007, she’s been playing with her favorite toys – a dissecting microscope and mica Pieces she was dividing into sheets.
“When I looked at the bits of green algae and raw brown on the edges of the mica sheets, I thought this would be a good place for life to originate,” she said in an article she wrote for NSF about her work.
Her idea includes elements from other notions of phylogeny (how life arose from nonliving matter), asserting that precursors to biomolecules and metabolic processes All of them would have been contained between layers of mica. It is an environment that provided some protection from the outside world, but allowed the free exchange of water and other substances that would otherwise become essential to cells.
“My picture is that the surfaces of the mica sheets were a great place for molecules to grow and processes to develop, and in the end all that life needed was on the mica,” she said. Essentially, mica served as scaffolding and “reaction chambers”, where metabolic processes could occur and develop. Hansma added that the advantage of mica clay over montmorillonite is that it contains mica potassium ions When the mica sheets are held together, they are not bulging and thus provide a more stable environment. In contrast, the montmorillonite sheets are held together by smaller sodium ions, which leads to shrinkage and swelling during wet dry cycles and a less stable environment.
The presence of potassium ions in microscopic clay is another factor in favor of the mica clay hypothesis: cells in living organisms have high intracellular potassium concentrations, making mica “a more likely home to the origins of life than montmorillonite.”
And where would this prebiotic assembly obtain the energy to react and maintain itself in the absence of the biochemical energy that now powers our bodies? At the time, sunlight was one filter, Hansma suggests, as would mechanical energy, through the opening and closing of the mica sheets as water flowed in and out.
“It appears that these open and closed motions were ways to smash molecules together, before there was chemical energy,” she said. This forced convergence could have enhanced intermolecular interactions, similar to the actions of enzymes today. Different interacting molecules combine to form RNA, DNA, and proteins. The lipids in the mixture will eventually wrap around the clusters of large molecules and become the cell membrane.
These are just a few of the arguments in Hansma’s hypothesis that give way to life after I started in the exact mud. Further support can be found in the aging of mica, in the affinity of the mineral with biomolecules and other factors believed to have promoted the evolution of life from inanimate molecules.
Although we’re not likely to know for sure what happened nearly 4 billion years ago, it’s clear – says Hansma – that “life imitates mica in many ways.”
Helen Greenwood Hansma, DNA and the Origins of Life in Mud Clay, Biophysical Journal (2022). DOI: 10.1016 / j.bpj.2022.08.032
University of California – Santa Barbara
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