I re-read eerie silence every couple of years. Paul Davies is a phenomenal writer. I never even knew about chirality playing a role in looking for life on Mars (basically all Earth DNA from anything has always shown the helix to twist in one direction, but there is no reason why it can't go the other way, so if we find DNA on another planet that twists the other way, it is extremely unlikely to be a contaminant brought on the probe from earth).
