In mythologies and origin stories around the world, various cultures and religions point to clay as the vessel of life, the primordial material that the creator gods imbued with a self-sufficient existence. Nowadays we have the biology to explain how life is born, but could these old tales hit more to the mark than we think?
In an article written to commemorate the work of Ned Seeman, inventor of the field of DNA nanotechnology, UC Santa Barbara emeritus biophysics Helen Hansma outlines his long-held idea that that primitive life, in precellular arrangements that evolved into the our organism based on lipids and protein cells, may have originated in the micaceous clay. Her card appears in Biophysical Journal.
Originally proposed nearly 16 years ago, Hansma’s hypothesis joins many other speculations about how life on Earth came about. Among these are the famous “World of RNA”, in which self-replicating RNA molecules evolved into DNA and proteins, and the “Before metabolism” concept, which says that life evolved from spontaneous chemical reactions. There is also a “pizza” hypothesis which states that life could come from terrestrial organic biomolecules. And there are other clay hypotheses that state that life may have originated on montmorillonite clay or iron-rich clays.
Hansma didn’t decide to understand how life on Earth evolved when he first came up with his idea. Rather, as a research biophysicist and program director at the National Science Foundation around 2007, she was playing with her her favorite toys: a dissecting microscope and bits of mica that she was dividing into sheets.
“As I looked at the bits of green and rough brown algae at the edges of the mica sheets, I thought, ‘this would be a good place to give birth to life,'” he said in an article written for NSF about his work.
His idea incorporates elements of other concepts of abiogenesis (how life emerged from non-living material), stating that the precursors of biomolecules and metabolic processes could all have been enclosed in layers of mica. It is an environment that offered some protection from the outside world, but allowed the free exchange of water and other substances that would become essential for the cells.
“My picture is that the surfaces of the mica sheets were an ideal place for molecule growth and process development, and ultimately everything needed for life was on the mica,” he said. In essence, mica served as scaffolding and “reaction chambers”, where metabolic processes could occur and evolve. The advantage mica clays have over montmorillonite, Hansma added, is that micas, with potassium ions holding the mica sheets together, do not swell and thus provide a more stable environment. Montmorillonite sheets, on the other hand, are held together by smaller sodium ions, resulting in shrinkage and swelling during wet-dry cycles and a less stable environment.
The presence of potassium ions in the mycaceous clay is another factor in favor of the mycaceous clay hypothesis: cells in living creatures have high intracellular concentrations of potassium, making mica “a more likely habitat for the origins of life than the montmorillonite “.
And where would this prebiotic assemblage get the energy to interact and sustain itself in the absence of the biochemical energy that now powers our bodies? At the time, sunlight would have been a candidate, Hansma suggests, as would mechanical energy, through opening and closing mica sheets as water flowed in and out.
“It appears that these opening and closing movements were ways of squeezing molecules together, before chemical energy existed,” he said. This forced proximity may have promoted interactions between molecules, similar to the actions of today’s enzymes. Several interacting molecules would join together to form RNA, DNA and proteins. The lipids in the mixture would eventually envelop the large molecule clusters and become the cell membrane.
These are just some of the arguments of Hansma’s hypothesis that lend themselves to life having started in micaceous clay; other support can be found in the old age of mica and in the mineral’s affinity for biomolecules and other factors that are thought to have promoted the development of life from non-living molecules.
While it’s not likely we’ll ever know for sure what happened nearly 4 billion years ago, it’s clear that – as Hansma puts it – “Life imitates mica in many ways.”
Mica provides clues to how water carries minerals
Helen Greenwood Hansma, DNA and the origins of life in micaceous clay, Biophysical Journal (2022). DOI: 10.116 / j.bpj.2022.08.032
Provided by the University of California – Santa Barbara
Citation: Did life begin in micaceous clay? (2022, September 20) retrieved September 22, 2022 from https://phys.org/news/2022-09-life-micaceous-clay.html
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