As noted previously there are many descriptions of what is life, but they all require recognition of the need for reproduction. Reproduction however requires adding order to the universe. This reduces something called entropy which can’t happen spontaneously. It doesn’t mean it can’t happen at all, only it can’t happen spontaneously. The way to make it happen is to add energy (synonymous with work.)
A rock will spontaneously roll down a hill, but to get it back up the hill requires work. It’s the same way with chemistry, there are two kinds of reactions: those that go “downhill” and give off energy in the process (exothermic) and those that have to be driven “uphill” by putting energy into the system (endothermic.)
I mentioned entropy as it is an organizing principle in the universe. Entropy is often referred to as “time’s arrow.” You can tell time by watching sand fall through an hourglass. This is a spontaneous process so time is moving in the proper direction.
Back to creating life. We have to have a molecule (or molecular system) that can reproduce itself, but that process is energetically uphill so we need a source of energy to drive the process. The earliest hypotheses about the beginning of life focused on the oceans as a warm chicken soup of ingredients but didn’t address the necessity of an energy source.
Life began during the Archean period, three and a half to four billion years ago. Times were different then. The earth’s surface and atmosphere chemically much different then but there could have been energy-rich molecules and reactions available to drive the self-assembly of life’s molecules.
This is not dissimilar to how life sustains itself today. To build the complex molecules that we need every day requires a process of combining two kinds of reactions. The chemical reactions we need to build protein for example are very endothermic, that is, energetically uphill. If we combine this reaction with one that is energetically downhill, exothermic, we can make it happen. Foods such as fats and carbohydrates can be used to produce the chemical energy (exothermic reactions) we need to drive the endothermic process of protein synthesis.
We need to combine the replication of an RNA-like molecule with certain reactions that give off energy to drive the process. Those ingredients are present around what are called “white smokers.” These are vents in the ocean floor that continuously emit gases that can combine exothermically. Couple these reactions with our RNA-like molecule and everything needed to sustain life is present.
These two approaches to the beginning of life are little more than the reiteration of what sustains life – reproducing molecules, and energy providing molecules. From my perspective, the process is simple and straightforward and therefore is likely to have occurred more than once. Life could have started several times over but ultimately only one survived, as is indicated by the fact that every living thing is related through our DNA. From the smallest bacteria to every plant and animal. We all share the same genetic code and operate on the same principles of reproduction driven by chemical reactions producing energy. In other words, we are one.
Dr. Bob Allen is Emeritus Professor of Chemistry, Arkansas Tech University.