Earth, four billion years ago, was a lifeless, hot and violent place. Not exactly a world where you’d expect life to form. But this was the scene where the first life-forming amino acids appeared. And how did this happen? According to new research, a lump of rock floating though space may have been irradiated by neutron star emissions, chemically altering amino acids hitching a ride on it. This rock then impacted the Earth and injected these altered chemicals into the desert wastes, possibly seeding the beginning of life on our planet… and this life was left-handed…
We’ve heard about this possibility before: life on Earth being seeded by some extra-terrestrial body, like a comet, meteorite or asteroid impact. In fact the prime reason for analysing comets and objects in the Oort Cloud (hovering around the outer reaches of our solar system) is to look for pre-life chemicals and organic compounds such as amino acids. Indeed, the discovery of organic compounds by the recent Cassini flyby of Saturn’s moon last month is another piece in the puzzle toward understanding the extent of life-giving chemicals on planets other than Earth.
Amino acids are a type of protein found in all life forms on Earth, it seems reasonable to search for the presence of these proteins on bodies other than our planet, possibly giving us more information about how life formed and where life came from.
There are two forms of amino acids, one left-handed and one right-handed, giving an indication of the orientation of the acid. For life to be seeded, these proteins must contain only one “chirality” (i.e. either left or right), it’s no good having mixed chirality.
At the 235th national meeting of the American Chemical Society, new research has been presented describing how our amino acid signature may have come from outer space. Ronald Breslow, a university professor at Columbia University points out that the vast majority of life on Earth has a “left chirality”. And his reason for this? The polarized light emitted from neutron stars many billions of years ago irradiated rocky bodies, with amino acid compounds on their surface, selectively destroying most of the “right-hand” acids. Although this theory may sound outlandish, it does give a possible reason for the prevalence of left-hand proteins in amino acids on Earth.
The irradiated meteorite will have impacted the Earth carrying amino acids with a dominance of left chirality which dropped into the “primordial soup”, evolving into the first forms of life. All life as we know it will have the same chirality as this soup of pre-biotic life.
“These meteorites were bringing in what I call the ‘seeds of chirality’ […] If you have a universe that was just the mirror image of the one we know about, then in fact, presumably it would have right-handed amino acids. That’s why I’m only half kidding when I say there is a guy on the other side of the universe with his heart on the right hand side.” – Ronald Breslow.
Breslow and his team simulated the events after such a meteorite hit the surface. As the left-hand dominated amino acids from space combined with existing amino acids (of mixed chirality) on Earth, the desert-like temperatures and a dash of water amplified the left-hand proteins, giving them dominance, thus sparking the basic building blocks of life. He argues that these acids were most likely brought to Earth via meteorite, and not chemically altered by radiation in-situ, “…the evidence that these materials are being formed out there and brought to us on meteorites is overwhelming,” said Breslow.