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When the first life emerged on Earth, it may have had a helping hand from an unexpected source: urea, a chemical found in urine. The urea may have been a vital building block, used to make the first simple genes.

Life on Earth began at least 3.5 billion years ago. Nobody knows exactly how, but it is likely that simple chemicals gradually became more complex until they could assemble into crude living cells.

One of the most crucial steps must have been the formation of the first genes. Today, most organisms store their genes on DNA. However, many scientists believe that the first organisms used a similar molecule called RNA, which can do things that DNA can鈥檛, and that life began with an 鈥�RNA world鈥�.

The problem with the RNA world idea is that RNA is a complex molecule. It is a chain of smaller molecules called nucleosides and phosphates. As a result, it has been difficult to explain how it could have formed naturally, so some biochemists suspect that a simpler molecule must have come first.

Proto-RNA

鈥淭hen comes the question, what could the precursor to RNA be?鈥� says Thomas Carell at the Ludwig Maximilian University of Munich in Germany. 鈥淲e argue let鈥檚 start with just two molecules, formaldehyde and urea.鈥� Both are simple and are likely to have existed on primordial Earth.

Carell鈥檚 team has now used them to make a simple version of RNA. Previous experiments have shown that formaldehyde can be converted into sugars, including ribose 鈥� a key component of RNA 鈥� so Carell鈥檚 team focused on urea.

The team knew that simply heating urea causes individual urea molecules to link up into pairs and triplets. So it mixed these urea-based molecules with ribose and water and heated them to 95 掳C until the mixture dried out, then added more water. This simulated a volcanic pond drying out in the sun, then filling up again.

The result was molecules similar to nucleosides, which the team calls 鈥渦rea nucleosides鈥�. Follow-up experiments showed that they could be inserted into RNA molecules in place of the normal nucleosides. Crucially, the nucleosides in RNA can pair up with each other and the urea nucleosides could also do this, suggesting they could be used to store genetic information.

鈥淚t鈥檚 certainly a molecule that we could consider as an ancestor of RNA,鈥� says Carell.

There may even be traces of the urea nucleosides in modern organisms. Carell points out that modern organisms use more than 150 in certain kinds of RNA and they often contain chemicals derived from urea. 鈥淲e postulate that these non-canonical nucleosides are chemical fossils,鈥� says Carell, which have .

Later, the proto-RNA would have become more complex and begun working more precisely, eventually giving rise to true RNA. In a , Carell鈥檚 team describes ways to make the building blocks of RNA.