Origins of Life on Earth: How Molecular Fossils are the Key

Before life began on Earth, there were molecules. These molecules, while important building blocks, didn't possess the structure that characterizes life as we know today. Eventually, though, a few specialized molecules began replicating; this started a biochemical process that eventually led to the first organisms. Exactly how this happened, though, has long remained a mystery. Now, scientists have a new theory as to how life was jumpstarted on Earth.

In the early 1980s, researchers found that ribozymes, which are RNA enzymes, act as catalysts. This seemed to indicate that RNA could be both the blueprints and chemical catalysts that put those blueprints into action. Essentially, RNA could have triggered the rise of life.

Yet in order for RNA to spawn life, ancient RNA catalysts would have had to copy multiple sets of RNA blueprints nearly as accurately as modern-day enzymes. This seemed somewhat unlikely. Scientists calculated that it would take much longer than the age of the universe for randomly generated RNA molecules to evolve enough to achieve the modern level of sophistication.

In order to examine what might have caused life to start on our planet, the researchers conducted lab experiments which recreated ancient protein enzymes. These enzymes likely played a vital role in helping create life on Earth. In order to find out what these "fossil" enzymes were, though, the researchers created and superimposed digital three-dimension versions of two super-families of modern-day enzymes. They found that the enzymes have virtually identical cores. After extracting these cores, which they dubbed Urzymes, the scientists were able to view what probably started off as the first enzymes.

"Our results suggest that there were very active protein enzymes very early in the generation of life, before there were organisms," said Charles Carter, one of the researchers, in a news release. "And those enzymes were very much like the Urzymes we've made."

In fact, it's likely that Urzymes evolved from even simpler ancestors, tiny proteins called peptides. Over time, peptides co-evolved with RNA to give rise to more complex life forms. The RNA would have contained the instructions for life while the peptides would have accelerated key chemical reactions to carry out those instructions.

The findings are important for understanding the origins of life on Earth. Yet there are still a few questions; the research leaves open the question of exactly how these primitive systems managed to replicate themselves. Currently, the scientists hope further research will answer this question.

The findings are published in the Journal of Biological Chemistry.