Origin of Life

A new hypothesis for how life got started has been proposed, by Helen Hansma, of UC Santa Barbara.


Mica.

Here’s the essential problem. Cells work because they have membranes surrounding them. These membranes protect the cells from nasty outside things, keep the stuff that is supposed to be working together in the cell in one place, and also, provide a communication and transport boundary for what goes in and out of the cell (various molecules as well as information).

However, a lot of the mechanisms involved in cells involve making, maintaining, and using this membrane. It is all very integrated, and indeed, dare I use the word, complex. The membrane is not an afterthought. It is fundamental to the cell’s functioning and reproduction, but also, it derives and is maintained from the cell itself via many complicated processes.

The cell says: “I have a membrane, therefore I am a cell.”

Which came first, the cell or the cell membrane.

No man is an island. But a cell is.

Which came first, the cell or the membrane.

And so on. You get the point. For cells to get started, you’ve got to have a membrane. For membranes to exist you’ve got to have a cell. For this reason, origins of life research often involves ideas about what could serve the role membranes serve today. The latest idea is kinda cool.

Mica.

Helen Hansma’s idea is that early life-stuff was protected in spaces among the layers of mica, the flakey-glassy-laminated mineral we all loved to play with as kids.

The mica hypothesis suggests that these spaces would have been perfect protective areas, and the separation between the layers would have provided both identity as well as the potential for isolated variation, thus allowing for Darwinian evolution.

According to Hansma:

Some think that the first biomolecules were simple proteins, some think they were RNA, or ribonucleic acid, … Both proteins and RNA could have formed in between the mica sheets.

In this model, the mica is sitting around in the ocean, where there are tides, salts, and other good stuff.

(These findings were presented at a press briefing of the American Society for Cell Biology in Washington, D.C.)

Some of the evidence supporting this hypothesis:

  • RNA and many proteins and lipids in our cells have negative charges like mica.
  • RNA’s phosphate groups are spaced one half nanometer apart, just like the negative charges on mica…
  • Mica layers are held together by potassium. The concentration of potassium inside the mica is very similar to the concentration of potassium in our cells.
  • The seawater that bathed the mica is rich in sodium, just like our blood.
  • The heating and cooling of the day to night cycle as well as tidal forces would have caused the mica sheets to move up and down, and waves would have provided a mechanical energy source for molecular transport or movement inside the proto-cell.

Besides providing a more plausible hypothesis than the prebiotic oceanic “soup” model, Hansma said her new hypothesis also explains more than the so-called “pizza” hypothesis. That model proposes that biomolecules originated on the surfaces of minerals from the Earth’s crust. The “pizza” hypothesis cannot explain how the earliest biomolecules obtained the right amount of water to form stable biopolymers.

A biophysicist, Hansma has worked with mica for decades beginning with her work in biological Atomic Force Microscopy (AFM) in the late 1980s. “We put our samples on mica, because it is so atomically flat, so flat that we can see even bare DNA molecules as little ridges on the mica surface,” said Hansma. “The layered mineral is made of sheets so thin (one nanometer) that there are a million of them in a millimeter-thick sheet of mica.”

Hansma came upon her idea one day last spring when she was splitting some mica under her dissecting microscope. She had collected the specimens in a mica mine in Connecticut. The mica was covered with organic material. “As I was looking at the organic crud on the mica, it occurred to me that this would be a good place for life to originate — between these sheets that can move up and down in response to water currents which would have provided the mechanical energy for making and breaking bonds,” said Hansma.

She summed up her hypothesis of the origin of life by saying, “I picture all the molecules of early life evolving and rearranging among mica sheets in a communal fashion for eons before budding off with cell membranes and spreading out to populate the world.”

Comments

  1. #1 qetzal
    December 12, 2007

    I didn’t think mica itself was a new idea for abiogenesis. Wasn’t it first suggested as a possible organizing surface quite a few years ago?

    Maybe the novelty here is the idea of organizing between layers of mica, rather than on exposed mica surfaces. I’m guessing the latter is the “pizza” hypothesis.

  2. #2 Greg Laden
    December 13, 2007

    I think so, pizza vs. dagwood sandwich. also, the bit about the tides.

    There is not paper that I know of, just a press release. I’ll keep looking out for it.

  3. #3 qetzal
    December 13, 2007

    Well, I tried to find a reference to mica and abiogenesis that predates Hansma, but I couldn’t. So maybe I’m just misremembering some of the work on other minerals like clays.