Most people are at least passingly familiar with the theory of biological evolution. As a tool for understanding the world around us, biological evolution helps explain the bewildering variety of life seeded across the planet. Life, however, does not just happen; even the simplest living cells are home to countless reactions and processes, each of which must proceed in a strictly controlled manner to sustain life.
The theory about how these molecules and reactions eventually organized themselves into living cells is called the theory of chemical evolution, or the theory of abiogenesis. A Cambridge research group recently released findings that provide compelling evidence of the theory’s plausibility.
The biggest chemical player in abiogenesis is ribonucleic acid, or RNA. According to a piece published in New Scientist in 2011, RNA is important to chemical evolution for three reasons: it can store information, it can catalyze reactions and it can replicate itself.
RNA molecules that copy themselves are crucial to abiogenesis because the copying process can be viewed as analogous to reproduction. A single RNA molecule that wishes to copy itself must compete with other RNAs for substrates and then undergo the process of replication. This process is prone to errors which can change the structure of the RNA from one generation to the next. This creates two huge driving evolutionary forces – competition and descent with modification. These are the same forces that propel biological evolution and in the setting of abiogenesis they provide a potential pathway for the development of more and more complex reactions, eventually culminating in living cells.
The New Scientist article goes on to say that two of the biggest current problems with the theory of abiogenesis are that it is unclear where the precursor molecules for RNA would have come from and that RNA is limited in which sorts of reactions it can catalyze. The recent discovery at Cambridge addresses both questions.
The Cambridge team’s experiment was rather straightforward. According to a release, also in New Scientist, the team took a solution composed to mimic earth’s ancient oceans and added “substances known to be starting points for modern metabolic pathways.”
The samples were then heated to “between 50 ˚C and 70 ˚C – the sort of temperatures you might have found near a hydrothermal vent – for five hours.” The samples were then analyzed for their chemical content.
Researchers were blown away by what they found. Their samples contained chemicals indicating that a number of complex reactions had taken place – reactions that closely mimicked the internal metabolism that provides energy for living cells.
“In all,” said the New Scientist article, “29 metabolism-like chemical reactions were spotted, seemingly catalyzed by iron and other metals that would have been found in early ocean sediments.”
The prebiotic ocean water, when exposed to heat, underwent a series of reactions very similar to two chemical pathways called glycolysis and the pentose-phosphate pathway.
“Together these pathways produce some of the most important materials in modern cells,” said New Scientist, “including ATP – the molecule cells use to drive their machinery, the sugars that form DNA and RNA, and the molecules needed to make fats and proteins.”
The theory of Abiogenesis is a young theory. As such, it is quite open to revision and correction as new information is brought to light. The experiment carried out at Cambridge was successful in demonstrating a possible source of building blocks for the all-important RNA. It was also successful in illuminating the complex reactions which could have taken place spontaneously in Earth’s ancient oceans. While these two insights are far from an answer on the origins of life, they represent a step forward in our understanding of what is possible.
