Hot ocean water blamed for an­cient mass ex­tinc­tion

The Korea Times - - SCIENCE -

WASH­ING­TON ( AP) — Sci­en­tists think they’ve fig­ured out the fall­ing dominoes that led to Earth’s largest mass ex­tinc­tion and worry that hu­man-caused cli­mate change puts the planet on a vaguely sim­i­lar path.

Some 250 mil­lion years ago, about 90 per­cent of sea life and 70 per­cent of land life went ex­tinct in what is now called the Great Dy­ing. Sci­en­tists have long spec­u­lated that mas­sive vol­canic out­bursts trig­gered the cat­a­clysmic event, but how that worked was still a bit fuzzy. It wasn’t the lava it­self.

A new study in Thurs­day’s jour­nal Science used com­plex com­puter sim­u­la­tions to plot out what hap­pened af­ter the vol­ca­noes blew: It led to ocean tem­per­a­tures ris­ing by about 20 de­grees (11 de­grees Cel­sius), which then starved the sea­wa­ter of oxy­gen. That hot oxy­gen-starved water caused the mass marine die-off, es­pe­cially farther from the equa­tor.

Af­ter the vol­ca­noes blew, the level of heat-trap­ping car­bon diox­ide soared to a level more than 12 times what it is to­day , said study lead au­thor Justin Penn, an Earth sciences re­searcher at the Uni­ver­sity of Wash­ing­ton.

Water loses oxy­gen when it warms, much like a warm can of cola goes flat, Penn said. Sci­en­tists looked at dozens of modern species to see what hap­pens to them in warmer, oxy­gen-starved water and that helped them un­der­stand the past ex­tinc­tion.

One of the keys in the re­search is that more species died off away from the equa­tor. That’s be­cause trop­i­cal species were more ac­cli­mated to low oxy­gen lev­els, Penn said.

While hu­mans aren’t warm­ing the Earth any­where close to as much as what hap­pened nat­u­rally 250 mil­lion years ago, “this puts our fu­ture into the cat­e­gory of con­tenders for true catas­tro­phe,” said study co-au­thor Cur­tis Deutsch, an Earth sci­en­tist at the Uni­ver­sity of Wash­ing­ton.

The an­cient die-off “shows al­most ex­actly what lies at the end of the road we’re on,” Deutsch said. “We’re re­ally do­ing the same thing to Earth’s cli­mate and oceans.”

The study cal­cu­lates that if heat-trap­ping car­bon diox­ide emis­sions con­tinue on cur­rent lev­els, by the year 2300, the globe will ex­pe­ri­ence 35 to 50 per­cent of the ex­tinc­tion level seen in the Great Dy­ing.

Uni­ver­sity of Leeds pa­le­on­tol­o­gist Paul Wig­nall said no cur­rent global warm­ing sce­nario en­vi­sions 20 de­grees of warm­ing in the next few cen­turies, so it could be mil­len­nia away.

How­ever, even an event 10 per­cent as bad as the Great Dy­ing “would be dread­ful,” said Wig­nall, who wasn’t part of the study.

Other out­side sci­en­tists said the study pro­vides a scary glimpse into Earth’s pos­si­ble fu­ture.

“Be­cause we are warm­ing up the Earth at a rapid rate, re­sults from this study could prove to very use­ful in un­der­stand­ing” what hap­pens to life in fu­ture oceans, Uni­ver­sity of South­ern Cal­i­for­nia Earth sci­en­tist David Bot­tjer said in an email.

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