1. Religion & Spirituality
Send to a Friend via Email

Discuss in my forum

Austin Cline

Thermodynamics and the Origin of Life

By October 23, 2012

Follow me on:

One popular creationist argument is that the Second Law of Thermodynamics makes it impossible for life to develop naturally, without some sort of supernatural intervention. It's true that the mechanism for the origin of life is not yet know, but the solution may actually be in thermodynamics itself.

Progress of Evolution
Progress of Evolution
James Cotier / Getty Images

It's important to keep in mind that the real problem for how life could arise is energy: living things consume a lot more energy than your average batch of non-living chemicals. What's more, the first forms of life were probably less efficient that living things today.

So solving the problem of how life arose means solving the problem of how enough energy can be generated to power life.

The earliest cells seem to have gained their energy and carbon from the gases hydrogen and carbon dioxide. The reaction of H2 with CO2 produces organic molecules directly, and releases energy. That is important, because it is not enough to form simple molecules: it takes buckets of energy to join them up into the long chains that are the building blocks of life.

A second clue to how the first life got its energy comes from the energy-harvesting mechanism found in all known life forms. This mechanism was so unexpected that there were two decades of heated altercations after it was proposed by British biochemist Peter Mitchell in 1961.

Mitchell suggested that cells are powered not by chemical reactions, but by a kind of electricity, specifically by a difference in the concentration of protons (the charged nuclei of hydrogen atoms) across a membrane. Because protons have a positive charge, the concentration difference produces an electrical potential difference between the two sides of the membrane of about 150 millivolts.

It might not sound like much, but because it operates over only 5 millionths of a millimetre, the field strength over that tiny distance is enormous, around 30 million volts per metre. That's equivalent to a bolt of lightning. Mitchell called this electrical driving force the proton-motive force. It sounds like a term from Star Wars, and that's not inappropriate. Essentially, all cells are powered by a force field as universal to life on Earth as the genetic code. This tremendous electrical potential can be tapped directly, to drive the motion of flagella, for instance, or harnessed to make the energy-rich fuel ATP.

Source: New Scientist, 23 June 2012

Of course, the first cells weren't doing all of this entirely on their own because they couldn't have had the internal mechanisms for it right from the start. So is there an external source of this energy that they could have tapped into before evolving the means for doing it on their own?

The answer I favour was proposed 20 years ago by the geologist Michael Russell, now at NASA's Jet Propulsion Laboratory in Pasadena, California, who had been studying deep-sea hydrothermal vents. Say "deep-sea vent" and many people think of dramatic black smokers surrounded by giant tube worms. Russell had something much more modest in mind: alkaline hydrothermal vents. These are not volcanic at all, and don't smoke. They are formed as seawater percolates down into the electron-dense rocks found in the Earth's mantle, such as the iron-magnesium mineral olivine.

Olivine and water react to form serpentinite in a process that expands and cracks the rock, allowing in more water and perpetuating the reaction. Serpentinisation produces alkaline proton poor - fluids rich in hydrogen gas, and the heat it releases drives these fluids back up to the ocean floor. When they come into contact with cooler ocean waters, the minerals precipitate out, forming towering vents up to 60 metres tall.

Such vents, Russell realised, provide everything needed to incubate life. Or rather they did, four billion years ago. Back then, there was very little, if any, oxygen, so the oceans were rich in dissolved iron. There was probably a lot more CO2 than there is today, which meant that the oceans were mildly acidic - that is, they had an excess of protons.

Just think what happens in a situation like this. Inside the porous vents, there are tiny, interconnected cell-like spaces enclosed by flimsy mineral walls. These walls contain the same catalysts - notably various iron, nickel and molybdenum sulphides - used by cells today (albeit embedded in proteins) to catalyse the conversion of CO2 into organic molecules. Fluids rich in hydrogen percolate through this labyrinth of catalytic micro pores.

Normally, it is hard to get CO2 and H2 to react: efforts to capture CO2 to reduce global warming face exactly this problem. Catalysts alone may not be enough. But living cells don't capture carbon using catalysts alone - they use proton gradients to drive the reaction. And between a vent's alkaline fluids and acidic water there is a natural proton gradient. Could this natural proton-motive force have driven the formation of organic molecules? It is too early to say for sure. I'm working on exactly that question, and there are exciting times ahead. But let's speculate for a moment that the answer is yes. What does that solve?

A great deal. Once the barrier to the reaction between CO2 and H2 is down, the reaction can proceed apace. Remarkably, under conditions typical of alkaline hydrothermal vents, the combining of H2 and CO2 to produce the molecules found in living cells - amino acids, lipids, sugars and nucleobases - actually releases energy.

That means that far from being some mysterious exception to the second law of thermodynamics, from this point of view, life is in fact driven by it. It is an inevitable consequence of a planetary imbalance, in which electron-rich rocks are separated from electron-poor, acidic oceans by a thin crust, perforated by vent systems that focus this electrochemical driving force into cell-like systems. The planet can be seen as a giant battery; the cell is a tiny battery built on basically the same principles.

Source: New Scientist, 23 June 2012

This certainly isn't a complete and final solution to the origin of life, but it does bring together all the elements necessary to solve a primary problem for the origin of life (energy generation) as well as the elements necessary for life itself. Having all the pieces in one place doesn't mean that the puzzle has been solved, but it does mean that a solution for the puzzle is possible.

No comments yet. Leave a Comment
Leave a Comment

Line and paragraph breaks are automatic. Some HTML allowed: <a href="" title="">, <b>, <i>, <strike>

©2014 About.com. All rights reserved.