By Hamish Johnston

Scientists have long wondered whether life originated on Earth or was seeded by biological-like molecules that arrived here from space. Meteorites could offer clues to this mystery because they are prime examples of extraterrestrial material that has made its way to our planet.

While such molecules have been discovered in meteorites since the 1960s, researchers could not be sure whether this is simply the result of contamination that occurred once the rocks reached Earth.

In this video, NASA scientist Michael Callahan explains why he and his colleagues are convinced that “DNA building blocks” discovered in 12 meteorites were formed in space – rather than being contamination picked up on the ground.