Scientists say the oxygen you just breathed in was once the deadliest poison on the planet, released by tiny microbes that accidentally wiped out most of the life around them in what geologists call t

The strangest fact about the air in this room is that it would have killed almost everything alive on Earth 2.5 billion years ago. Oxygen, the molecule sustaining every cell in the human body, was once a chemical weapon — a corrosive industrial bypro... [9377 chars]