AIR-STARVED soil could have been a key player in the largest extinction ever to strike Earth. The claim follows the discovery of a rare mineral in ancient soil collected from Antarctica.
The extinction, at the end of the Permian period 250 million years ago, wiped out virtually all marine life and some 70 per cent of land animals. But the reason for the extinction, which preceded the rise of the dinosaurs, has been a long-standing puzzle.
Now Greg Retallack and his team of geologists at the University of Oregon think they have found what could be a major factor in the extinction. Retallack collected fossilised soil samples that formed in Antarctica just after the Permian period ended. The soil contained nodule-shaped minerals that Retallack鈥檚 student, Nathan Sheldon, identified as berthierine.
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This iron-rich mineral forms only in environments where oxygen is scarce. If the oxygen levels in the soil were low enough to allow berthierine to form, the soil would not have been able to support plant life, says Retallack (Geology, vol 30, p 919). 鈥淵ou鈥檝e got intolerably low levels of oxygen,鈥� he says. 鈥淚t would be enough to kill [the plants] off completely.鈥�
A drop in oxygen in the soil backs up a leading theory that a key factor in the mass extinction was a huge release of methane gas from frozen sheets of methane and water, called methane hydrate, found mainly under seabeds. Once released, clouds of methane would quickly cut oxygen levels in the atmosphere and soil by converting it into carbon dioxide.
The collapse of plant life would soon have caused large numbers of animals to starve. Methane bubbling up from seabeds into the air above could also have depleted the oxygen in the water, killing off marine life.
快猫短视频s still aren鈥檛 sure what could have triggered such a huge methane release, though. An asteroid strike could have released the gas by breaking up sheets of methane hydrate, but there is no evidence of an impact at that time. Other possibilities are massive volcanic eruptions, or climate change that thawed the icy methane.