Has life started in Glimmerton?

In mythologies and origin stories around the world, various cultures and religions refer to clay as the vessel of life, the primordial material imbued by the creator gods with self-sustaining existence. We now have the biology to explain how life originates, but could these ancient tales get any closer than we think?

In a paper written to commemorate the work of Ned Seeman, inventor in the field of DNA nanotechnology, UC Santa Barbara biophysicist emeritus Helen Hansma outlines her longstanding idea that this primitive life evolved in precellular assemblies our development on lipids and proteins cells might have gotten its start in mica. Your paper appears in the Biophysical Journal.

Originally proposed nearly 16 years ago, Hansma’s hypothesis joins many other speculations about how life originated on Earth. Among them are the well-known “RNA world,” in which self-replicating RNA molecules evolved into DNA and proteins, and the “metabolism first” concept, which holds that life evolved from spontaneous chemical reactions. There is also a “pizza” hypothesis that claims that life could originate from terrestrial organic biomolecules. And there are other clay hypotheses that say life may have originated on montmorillonite clay or iron-rich clays.

Hansma didn’t want to find out how life evolved on Earth when she first came up with her idea. Rather, as a research biophysicist and program director at the National Science Foundation around 2007, she played with her favorite toys—a dissecting microscope and bits of mica that she split into sheets.

“As I looked at the pieces of green algae and the brown dirt on the edges of the mica sheets, I thought, ‘That would be a good place for life to arise,'” she said of her work in an article written for NSF.

Their idea incorporates elements of other concepts of abiogenesis (how life arose from inanimate matter) and suggests that progenitors of biomolecules and metabolic processes could all have been cooped up between layers of mica. It is an environment that provided some protection from the outside world, but still allowed the free exchange of water and other substances that would become essential to cells.

“My picture is that the surfaces of mica sheets were a great place for molecules to grow and processes to evolve, and eventually everything needed for life was on the mica,” she said. Essentially, the mica acted as a scaffold and “reaction chamber” in which metabolic processes could take place and develop. The advantage of mica clays over montmorillonite, Hansma added, is that with potassium ions holding mica sheets together, micas don’t swell and therefore provide a more stable environment. In contrast, montmorillonite sheets 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 mica clay is another factor supporting the mica clay hypothesis: the cells in living things have high intracellular concentrations of potassium, making mica “a more likely habitat for the origin of life than montmorillonite.”

And where would this prebiotic assemblage get the energy to interact and sustain itself if it lacked the biochemical energy that now powers our bodies? At the time, sunlight would have been a candidate, Hansma suggests, as would mechanical energy from the mica sheets opening and closing as water flows in and out.

“It seems that these opening and closing movements were ways of squeezing molecules together before there was chemical energy,” she said. This forced proximity may have encouraged interactions between the molecules, similar to the actions of enzymes today. Different interacting molecules would combine to form RNA, DNA and proteins. Eventually, lipids in the mixture would wrap around the groups of large molecules and become the cell membrane.

These are just some of the arguments in Hansma’s hypothesis that life began in Glimmerton; Further support is found in mica’s old age and in the mineral’s affinity for biomolecules and other factors thought to have encouraged the evolution of life from non-living molecules.

While it’s unlikely we’ll ever know for sure what happened almost 4 billion years ago, it’s clear that – as Hansma says – “life mimics mica in many ways”.