When the Earth was born, it was a mess. Lightning storms and meteors likely bombarded the planet’s surface, a barren wasteland with little but chemicals present. How life formed amid such chaos is a mystery billions of years old. Now, a new study offers evidence that the first building blocks may have matched their environment, evolving in a less orderly way than previously thought.
“Years ago, the naive idea that pools of pure concentrated ribonucleotides might be present on the primitive Earth was mocked by [famed British chemist] Leslie Orgel as ‘the molecular biologist’s dream,’” said Jack Szostak, a Nobel Prize laureate, professor of chemistry and chemical biology and genetics at Harvard University, and investigator at the Howard Hughes Medical Institute. “But how relatively modern homogeneous RNA could emerge from a heterogeneous mixture of different starting materials was unknown.”
In a paper recently published in the Journal of the American Chemical Society, Szostak and colleagues present a new model for how RNA could have emerged. Instead of a straightforward path, he and his team propose a beginning that recalls the mishmash creation of Frankenstein’s monster, with RNA growing out of a mixture of nucleotides with similar chemical structures: arabino-, deoxy-, and ribonucleotides (ANA, DNA, and RNA).
The odds are exceedingly low that a perfect version of RNA formed automatically in the Earth’s chemical melting pot, Szostak said. It’s far more likely that many versions of nucleotides merged to form patchwork molecules with bits of both modern RNA and DNA, as well as largely defunct genetic molecules, such as ANA. These chimeras may have been the first steps toward today’s RNA and DNA, along with proteins.