Scientists have discovered exciting new evidence that life on Earth may have been delivered by comets from deep space. Repeated detections of a biologically important amino acid have been made by Europe’s Rosetta mission to Comet 67P/Churyumov-Gerasimenko. 

Organic compounds that are ingredients for life had previously been found in dust on the surface of the comet, which the Rosetta probe has been orbiting for nearly two years.

But the finding of the amino acid glycine in the fuzzy atmosphere around the comet is a major discovery because it is commonly found in proteins. Phosphorous has also now been detected – a vital element of all living organisms because it is a key component of DNA and cell membranes, where it transports chemical energy for metabolism.

The planets, including Earth, were bombarded with comets and asteroids in the early days of the Solar System, 3.8 billion years ago. Scars can still be seen as craters on the Moon, but Earth’s have been eroded away.

Scientists say the latest findings suggest the ingredients of life may have formed within interstellar, icy dust grains before becoming bound up in comets. The Solar System is thought to be surrounded by a vast reservoir of billions of comets.

Rosetta’s project scientist Matt Taylor said: “The multitude of organic molecules already identified by Rosetta, now joined by the exciting confirmation of fundamental ingredients like glycine and phosphorous, confirms our idea that comets have the potential to deliver key molecules for prebiotic chemistry.

“Demonstrating that comets are reservoirs of primitive material in the Solar System and vessels that could have transported these vital ingredients to Earth, is one of the key goals of the Rosetta mission, and we are delighted with this result.”

However, a note of caution about the findings has been sounded by astrobiologists. Leading authority Dr Lewis Dartnell, a research fellow at the Space Research Centre, University of Leicester, told Skymania: “My main feeling is that it’s risky to conflate finding organic molecules in comets with ‘life on Earth was delivered from space’.

“Firstly, the fact that astrochemistry produces organic molecules which then become incorporated into comets doesn’t necessarily mean that such extraterrestrial compounds were involved in the origin of life on Earth. If the ISM (interstellar medium) can produce organics, there is likely to have been a far greater repertoire created in the warm watery, chemistry-friendly, oceans of the primordial Earth.

“Organics in comets/meteorites tells you more about the ease of carbon chemistry than the source of organics for the origin of life on our planet. But more importantly, I think, there is a huge difference between prebiotic compounds like amino acids and delivery of life itself. Cells are unimaginably more complex than a pool of monomers like amino acids and nucleobases.”