After two years of collecting data, the team behind the Rosetta mission has made an interesting announcement today. The Rosetta probe has indicated that the comet it has been studying contains glycine, which is an amino acid considered to be one of the building blocks of life, as well as phosphorous which would be required to form primordial DNA. And while this is far from being life itself, it adds more weight to the theory that life could not only form in other regions of space, but that life on Earth may itself have an extraterrestrial origin.

For several decades now scientists have speculated on the origin of amino acids on the early Earth. It has been known for over forty years that these precursors to proteins can be formed in violent reactions that occurred five billion years ago in the first oceans. If the right chemicals are present in the water, and there is enough energy from thermal energy or possibly even from electrical storms, the reactions that form amino acids can occur. 

However there is another very interesting possibility. The Earth was bombarded by comets and asteroids throughout its history, and there has long been speculation that some of these objects could have brought complex molecules from elsewhere in the solar system (or beyond). Scientists already knew that comets and asteroids can contain water and simple molecules such as would be found in the primordial oceans, but the latest discovery by Rosetta proves that they can also contain organic molecules that are required to form life. (A similar result was actually published ten years ago by NASA's Stardust mission, but in that experiment there was contamination of the samples and so it remained uncertain whether the amino acids were from the comet or from Earth. With the Rosetta mission there is no hint of contamination.)

According to the team monitoring Rosetta, over the past two years it has made repeated detections of glycine being emitted into the halo of dust and gas that surrounds the comet. And while this comet will exit the solar system again without leaving any large remnants behind on Earth, other comets that passed through the Earth's orbit a few billion years ago could have left clouds of amino acids and other complex molecules that would fall to the Earth's surface, or even collided with the Earth and deposited their full load of organic molecules.

It is an interesting result, and perhaps a clue as to the origins of life itself!