Oxygen-depleted toxic oceans blamed for mass extinction 200mn years ago

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Researchers have established through a new study that oxygen-depleted toxic oceans have had a key role to play in mass extinction over 200 million years ago when half of the plants, animals and marine lives on the Earth perished.

The team from University of Southampton found that a condition called “marine photic zone euxinia” took place in the Panathalassic Ocean – the larger of the two oceans surrounding the supercontinent of Pangaea. The Pangaea supercontinent existed during the late Paleozoic and early Mesozoic eras. It formed approximately 300 million years ago and then began to break apart after about 100 million years.

Photic zone euxinia occurs when the sun-lit surface waters of the ocean become devoid of oxygen and are poisoned by hydrogen sulphide – a by product of micro-organisms that live without oxygen that is extremely toxic to most other life forms, said the paper that appeared in the journal Geology.

As tectonic plates shifted to break up Pangaea, huge volcanic rifts would have spewed carbon dioxide into the atmosphere, leading to rising temperatures from the greenhouse effect.

“The rapid rise in CO2 would have triggered changes in ocean circulation, acidification and deoxygenation,” said professor and co-author Jessica Whiteside.

These changes have the potential to disrupt nutrient cycles and alter food chains essential for the survival of marine ecosystems.

“Our data now provides direct evidence that anoxic, and ultimately euxinic, conditions severely affected food chains,” Whiteside commented.

The same CO2 rise that led to oxygen depleted oceans also led to a mass extinction on land, and ultimately to the ecological take-over by dinosaurs, the authors noted.

Although the Earth was very different during the Triassic period compared to today, the rate of carbon dioxide release from volcanic rifts are similar to those that we are experiencing now through the burning of fossil fuels.

“The consequences of rapidly rising CO2 in ancient times inform us of the possible consequences of our own carbon dioxide crisis,” Whiteside concluded.