For more than 150 years, scientists have known that the most basic building blocks of life – chains of amino acid molecules and the proteins they form – almost always have the unusual characteristic of being overwhelmingly "left-handed."
The molecules, of course, have no hands, but they are almost all asymmetrical in a way that parallels left-handedness.
This observation, first made in the 1800s by French chemist Louis Pasteur, is taught to introductory organic chemistry students – until recently with the caveat that nobody knew how this came to be.
But research into the question has picked up in recent years, focusing on a 200-pound chunk of rock found 40 years ago in Murchison, Australia. A meteorite that broke off an asteroid long ago, it brought to Earth a rich collection of carbon-based material from far away in the solar system. According to a report in Washington Post, while the Murchison meteorite does not have any once-living material, it is telling researchers new things about how life may have started on Earth, and how that almost universal protein left-handedness came to be.
The answer they believe they have found is that 3 billion to 4 billion years ago, before life on Earth began, similar meteorites crashed regularly into the planet – delivering the amino acids that would later be incorporated into all living things. – phenomica