Apr 25 2014

Prebiotic Earth

One of the great scientific mysteries is the specific processes and pathways that led to the first living organisms on earth. This is not mysterious in that we don’t know how it could have happened, it’s just that it is extremely difficult to reconstruct how is actually did happen. Chemical reactions don’t fossilize, and so understanding a complex process that likely took millions of years to unfold billions of year ago is a bit challenging.

Researchers have mostly had to rely on plausibility studies – experiments that show how prebiotic evolution could have happened and extrapolating from data on early earth conditions. More progress has been made with this type of research. The title of the paper says it all – Non-enzymatic glycolysis and pentose phosphate pathway-like reactions in a plausible Archean ocean. (Markus A. Keller, Alexandra V. Turchyn, Markus Ralser)

The researchers showed that, in conditions based upon published literature about the early prebiotic ocean, certain metabolic pathways central to life could happen spontaneously and without the presence of enzymes. That last bit is critical – enzymes are proteins that act as catalysts, which are substances that make a chemical reaction happen faster. Enzymes are critical to life, as the biochemical reactions of life would occur at too slow a rate without them.

Creationists are fond of making the “irreducible complexity” argument that life could not occur without enzymes, and enzymes are created by life, so how could such a system ever start? The basic answer is that without enzymes biochemical reactions are slow, but not nonexistent. They still occur. So prebiotic chemistry and even early life could have still used these reactions, but they would have been very slow and inefficient. Life could then simmer along and evolve the more sophisticated metabolic machinery we see today.

The current research demonstrates this principle. In fact, it demonstrates that metals, such as iron, under conditions likely to be present in the prebiotic ocean, would act as catalysts for certain metabolic pathways central to life, “glycolysis and pentose phosphate pathway-like reactions.” These critical reactions would occur at a functional rate without enzymes.

Further, the authors make a plausible argument based upon their findings that much of the basic metabolic pathways that make up living organisms could have been going on in the prebiotic oceans without life. In other words, metabolism itself predates the first life. The early oceans could have been “primordial soups” of chemical reactions, creating many of the building blocks of life.

Their research is also compatible with other research showing that primitive RNA was plausibly the earliest replicating molecule.

While we currently do not have the ability to peer back into time and see what was actually happening on earth 4 billion years ago, scientists have painted a fairly compelling picture of at least the broad brushstrokes of how life could have arisen. The early oceans had all the ingredients of life. These ingredients spontaneously form into the building blocks of life. RNA can arise spontaneously, and make copies of itself, setting into motion the potential for chemical evolution. And now we also can see that the metabolic reactions of life could have been humming along in the oceans of early earth before life arose.

Now all we need is for bubbles of bilipid membranes to spontaneously occur, which they do, encasing RNA, the metabolic soup, and amino acids and other building blocks of living cells. We don’t quite have a living cell yet, but we have a plausible precursor to a cell. Another point that creationists often miss is that scientists do not claim that a modern cell came together spontaneously, just the raw ingredients. From this point we still need hundreds of millions of years to evolve the complex machinery of a modern living cell.

It still seems amazing that the machinery of life could bootstrap itself into existence in this way. How did RNA learn to direct the synthesis of proteins, for example? That was a huge step in developing life’s machinery. I predict future research will shed further light on this process, like showing how such direction could occur spontaneously, although very slowly and crudely.

That is all you need, however. Once RNA has the tiniest toehold on the direction of protein synthesis, we are off to the evolutionary races. That creates an evolutionary feedback loop – RNA essentially catalyze and direct the creation of proteins from amino acids, and these proteins help the RNA do just that, as well as replicate itself, and then take over catalysis of the biochemical reactions that are already happening, create surface proteins to affect the internal environment of the evolving cell, proteins to help direct and control activity within the cell, and then more and more sophisticated protein structures.

Every tiny incremental step would have been a huge evolutionary advantage. There is no irreducible complexity here – we have pieces of the puzzle all the way back to spontaneous prebiotic reactions. We don’t have all the pieces to the puzzle, not even close, but we have enough to say that there is no irreducible complexity to the metabolism of life.

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