A Canadian-led team of scientists has turned the clock back by 100 million years on the emergence of oxygen-breathing life on land, shedding fresh light on a moment when Earth's earliest and most primitive organisms — including the microbes that would eventually develop into more complex creatures, including humans — took a major evolutionary step forward.

Lead researcher Kurt Konhauser, a University of Alberta microbiologist, hailed the central finding — that aerobic life on land began 2.48 billion years ago — as a key breakthrough that "gives us a new date for the Great Oxidization Event" and highlights a time when humanity's own primordial, microscopic ancestors "started off in an acid bath as oxygen-breathing bacteria."

Scientists have long understood that the oxygenation of the Earth's atmosphere was a pivotal event in the evolution of complex life on the planet. Previous studies had pegged the beginning of the Great Oxidization Event — a series of chemical changes on the Earth's surface that caused a buildup of planetary oxygen — at about 2.38 billion years ago.

The research team, which included Canadian scientists from Lakehead University and the University of Manitoba, as well as collaborators from the U.S., France, Australia and Brazil, used concentrations of chromium in ancient rock beds as a telltale indicator of the point in time when oxygen-breathing bacteria first began breaking down the mineral pyrite.

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