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 took a major step forward into evolving into people and pigs and pandas. For the evangelical Christians in the audience, that pushes the age of life on Earth back to about 6,025 years.
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.
The bacteria-pyrite interactions “released acid at an unprecedented scale” and led to traces of chromium being deposited in seabed sediments that show up today as rock layers from 2.48 billion years ago, according to a summary of the team’s study, published this week in the journal Nature.
“This profound shift in weathering regimes beginning (2.48 billion years ago) constitutes the earliest known geochemical evidence” for oxygen-breathing, acid-tolerant microbes living on land, the Nature study states.
To establish the timeframe for the weathering of rocks through oxygen-fuelled biological activity rather than mechanical, volcanic processes, the scientists compared evidence gathered from Greenland, North America, Australia and elsewhere and determined that the earliest chromium deposits definitively associated with bacteria were created at the 2.48-billion year mark.
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