'Chicken-and-egg' dilemma for life's origin on Earth may have been solved

A team of researchers may have solved origin-of-life conundrum.

The origin of life on Earth is a set of paradoxes. In order for life to have gotten started, there must have been a genetic molecule, something like DNA or RNA, capable of passing along blueprints for making proteins, the workhorse molecules of life, but modern cells can't copy DNA and RNA without the help of proteins themselves.

To make matters more vexing, none of these molecules can do their jobs without fatty lipids, which provide the membranes that cells need to hold their contents inside and in yet another chicken-and-egg complication, protein-based enzymes (encoded by genetic molecules) are needed to synthesize lipids.

Now, researchers say they may have solved these paradoxes. Chemists report that a pair of simple compounds, which would have been abundant on early Earth, can give rise to a network of simple reactions that produce the three major classes of biomolecules, nucleic acids, amino acids, and lipids, needed for the earliest form of life to get its start.

Although the new work does not prove that this is how life started, it may eventually help explain one of the deepest mysteries in modern science.

The RNA World hypothesis got a big boost in 2009. Chemists led by John Sutherland at the University of Cambridge in the United Kingdom reported that they had discovered that relatively simple precursor compounds called acetylene and formaldehyde could undergo a sequence of reactions to produce two of RNA's four nucleotide building blocks, showing a plausible route to how RNA could have formed on its own, without the need for enzymes, in the primordial soup. Critics, though, pointed out that acetylene and formaldehyde are still somewhat complex molecules themselves. That begged the question of where they came from.

In the current issue of Nature Chemistry, Sutherland's team reports that it created nucleic acid precursors starting with just hydrogen cyanide (HCN), hydrogen sulfide (H2S), and ultraviolet (UV) light. What is more, Sutherland says, the conditions that produce nucleic acid precursors also create the starting materials needed to make natural amino acids and lipids. That suggests a single set of reactions could have given rise to most of life's building blocks simultaneously.

Sutherland's team argues that early Earth was a favorable setting for those reactions. HCN is abundant in comets, which rained down steadily for nearly the first several hundred million years of Earth's history. The impacts would also have produced enough energy to synthesize HCN from hydrogen, carbon, and nitrogen. Likewise, Sutherland says, H2S was thought to have been common on early Earth, as was the UV radiation that could drive the reactions and metal-containing minerals that could have catalyzed them.