Modern scientists have determined that life originated from single celled organisms. They also believe that over millions of years these cells grew in complexity, eventually giving rise to the biological diversity that colours our world today. Through genome sequencing we can be fairly certain about the dates at which organisms originated and how far back species are related.
What isn’t as easy to determine is how those single-celled organisms sprang into existence. The current — and much contested — theory, called the abiogenesis or “spontaneous generation” theory, posits that life arose when molecules began to self-replicate. According to the theory, simple organic molecules arose in the early primordial sea and formed polymers — chains of molecules. Some of these polymers and polynucleotides, like primitive RNA for instance, began to self-replicate.
Many researchers claim that organic molecules simply cannot self-replicate and that this idea is the “Achilles heel” of the argument. However, scientists at the Ludwig Maximilians University of Munich believe they have found the answer behind the emergence of self-replicating polymers.
First of all, it’s important to know something about the basic characteristics of RNA, or ribonucleic acid. RNA is unique in that it plays two roles in cell mechanics: it contains genetic information, and it catalyzes reactions. Most of us are familiar with RNA as a “go-between”: transporting genetic information in the form of base-pairs between DNA and protein. However, it was only relatively recently discovered that in some cases RNA can also act as a catalyst for a chemical reaction, much like an enzyme — or in this case a “ribozyme.”
Abiogenesis gives us an explanation of evolution and genetic transmission starting with an already assembled strand of RNA. The current theory, as explained by Theory-of-Evolution.net, states that “conceptually RNA should be able to self-replicate without the help of proteins. [ . . . ] The original strand serves as a template. New base pairs arrive and form weak bonds with their complement. [ . . . ] After one replication, two complementary strands exist.” But there’s no explanation given as to how the original strand of RNA came to be.
Now, the group of scientists from Munich believe they have found the answer. It lies in an ancient naturally occurring system the team calls an “RNA Reactor.” Physorg.com writes: “The scene begins inside porous rocks on the sea floor, where strong temperature gradients produce thermal convection, and the convective flow transports molecules inside the narrow pores.” The team explains that long chains of molecules begin to form as a result of many random bond formations. The chains grow in length and complexity due to selective pressures inside the reactor, eventually creating complicated molecular chains, like RNA.
This is where the theory gets interesting. You may be thinking, “So, molecules get connected inside a rock. Big deal. It still doesn’t explain how self-replicating life came to be.” Or maybe you’re thinking of something entirely different — I can’t be sure. However, the team believes that through repetition, a primitive form of selection may have occurred inside the reactor.
The reactor provides an environment where the “fittest” molecule chains pass on their information — in the form of base-pairings — to another chain of molecules. This passing of information essentially prolongs the life of a particular sequence of base-pairs, conserving a particular piece of information for more than the lifespan of a single polynucleotide. Sound familiar yet?
The team proposes that eventually, over the course of many reactions, a simple self-replicating strand of RNA may have emerged. “Overall, the computer simulations showed that the prebiotic RNA reactor could serve as a stepping stone toward the emergence of a true RNA replicator. Acting as a filter to keep potentially useful sequences of nucleotides, the RNA reactor could lead to complex sequences, such as ribozymes. Once ribozymes emerge from an RNA reactor, they could establish an efficient self-replicating system in the form of an RNA replicator.”
If these results are verified, it could mean that we are getting ever closer to figuring out exactly how and when life arose. Unfortunately, even with the most precise instruments and most rigorously tested findings, we still won’t be able to know why.