"Long before it's in the papers"
January 27, 2015


Deadly heat baked pre-dinosaur world: study

Oct. 19, 2012
Courtesy of the University of Leeds
and World Science staff

Vi­cious heat made huge swaths of Earth vir­tu­ally un­liv­a­ble for fully five mil­lion years fol­low­ing its worst mass ex­tinc­tion, a new study in­di­cates.

Ac­cord­ing to the re­search, deadly high tem­per­a­tures simply cleared out the fish from huge ar­eas of ocean and are some­thing worth think­ing about as glob­al warm­ing stalks us even to­day.

Artist's con­cept of the end-Permian ex­tinc­tion, in which 90 per­cent of all ma­rine spe­cies are thought to have per­ished. (Cred­it: NA­SA Lu­nar & Plan­e­tary In­st.)

Around 250 mil­lion years ago the world wit­nessed the “end-Perm­ian mass ex­tinc­tion,” a dis­as­ter that wiped out nearly all spe­cies of life. The event al­so marked the be­gin­ning a new ge­o­log­ic pe­ri­od—the Tri­as­sic—which wit­nessed the first di­no­saurs, but that was some 20 mil­lion years lat­er.

In stark con­trast, the first five mil­lion years of the Tri­as­sic were a “dead zone,” sci­en­tists say. Typ­ic­ally, a mass ex­tinc­tion is fol­lowed by a dead zone dur­ing which new spe­cies aren’t seen for tens of thou­sands of years, they ex­plain, but in this case the dev­asta­t­ion lin­gered for mil­lions.

The new stu­dy in­di­cates a tem­per­a­ture rise to le­thal lev­els in the trop­ics caused the slow-mo­tion ca­tas­tro­phe. Tem­per­a­tures were an es­ti­mat­ed 50-60 de­grees C (up to about 122 de­grees F) on land, and 40 de­grees C (a­bout 104 de­grees F) at the sea sur­face.

The study is the first to show ocean sur­face tem­per­a­tures can go that high at all—some­thing experts did­n’t be­lieve, said Ya­dong Sun, the stu­dy’s lead au­thor, who is based at the Uni­vers­ity of Leeds in the U.K.  while com­plet­ing a joint doc­tor­ate in ge­ol­o­gy. Such a tem­per­a­ture nearly stops sea life in its tracks in part be­cause it shuts down pho­to­syn­the­sis, the pro­cess by which plants draw en­er­gy from sun­light, he added.

The study is pub­lished Oct. 19 in the re­search jour­nal Sci­ence

“No­body has ev­er dared say that past cli­mates at­tained these lev­els of heat. Hope­fully fu­ture glob­al warm­ing won’t get an­y­where near [that], but if it does... it may take mil­lions of years to re­cov­er,” said earth sci­ent­ist and study co-au­thor Paul Wig­nall of the Uni­vers­ity of Leeds.

“Global warm­ing has long been linked to the end-Permian mass ex­tinc­tion, but this study is the first to show ex­treme tem­per­a­tures kept life from re-starting in Equa­to­ri­al lat­i­tudes for mil­lions of years,” Sun said.

The dead zone would have been a strange world, ac­cord­ing to re­search­ers: very wet in the trop­ics but with al­most noth­ing grow­ing. No trees to offer a dol­lop of shade, only shrubs and ferns. No fish or ma­rine rep­tiles, only shell­fish, and vir­tu­ally no land an­i­mals be­cause their high met­a­bol­ic rate made it im­pos­si­ble to deal with the ex­treme tem­per­a­tures. Only the po­lar re­gions, the in­vest­i­ga­tors say, pro­vid­ed a ref­uge. 

The finding, Sun and col­leagues added, might help explain a signi­fi­cant dearth of coal deposits known from the Early Tri­assic. Coal comes from dead plants.

Be­fore the end-Permian mass ex­tinc­tion the Earth had teemed with plants and an­i­mals in­clud­ing prim­i­tive rep­tiles and am­phib­ians, and a wide va­ri­e­ty of sea crea­tures in­clud­ing cor­al and sea lil­ies.

Studies have reached differing con­clu­sions re­gard­ing whe­ther heat caused the ini­tial mass ex­tinction of the end-Perm­ian itself. Be that as it may, Sun and colleagues said the ravaging heat that followed was likely due to a break­down in glob­al car­bon cy­cling. Normal­ly, plants help reg­u­late tem­per­a­ture by ab­sorb­ing car­bon di­ox­ide and bur­y­ing it as dead plant mat­ter. With­out plants, lev­els of car­bon di­ox­ide can rise un­checked, which causes tem­per­a­tures to in­crease.

Sun and col­leagues col­lect­ed da­ta from 15,000 an­cient con­odonts, ti­ny teeth of ex­tinct eel-like fish­es, ex­tracted from two tons of rocks from South Chi­na. Con­odonts form a ske­l­e­ton us­ing ox­y­gen. The iso­topes, or vari­ants, of ox­y­gen in the skel­e­tons depend on tem­per­a­ture, so the lev­els of these iso­topes in the con­o­donts are be­lieved to give an es­ti­mate of ancient tem­per­a­tures.

* * *

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Vicious heat made huge swaths of Earth virtually unlivable for fully five million years following its worst mass extinction, a new study indicates. According to the research, deadly high temperatures simply cleared out the fish from huge areas of ocean and are something worth thinking about as global warming stalks us even today. Around 250 million years ago the world witnessed the “end-Permian mass extinction,” a disaster that wiped out nearly all species of life. The event also marked the beginning a new geologic period—the Triassic—which witnessed the first dinosaurs, but that was about 20 million years later. In stark contrast, the first five million years of the Triassic were a “dead zone,” scientists say. Typically, a mass extinction is followed by a dead zone during which new species aren’t seen for tens of thousands of years, they explain, but in this case the devastation lingered for millions. The new study, led by the University of Leeds in the U.K. and China University of Geosciences, indicates a temperature rise to lethal levels in the tropics caused the slow-motion catastrophe. Temperatures were an estimated 50-60 degrees C (up to about 122 degrees F) on land, and 40 degrees C (about 104 degrees F) at the sea surface. The study is the first to show ocean surface temperatures can go that high at all—something climate modellers didn’t believe, said Yadong Sun, the study’s lead author, who is based in Leeds while completing a joint doctorate in geology. Such a temperature nearly stops sea life in its tracks in part because it shuts down photosynthesis, the process by which plants draw energy from sunlight, he added. The study is published Oct. 19 in the research journal Science. “Nobody has ever dared say that past climates attained these levels of heat. Hopefully future global warming won’t get anywhere near [that], but if it does we have shown that it may take millions of years to recover,” said earth scientist and study co-author Paul Wignall of the University of Leeds. “Global warming has long been linked to the end-Permian mass extinction, but this study is the first to show extreme temperatures kept life from re-starting in Equatorial latitudes for millions of years,” Sun said. The dead zone would have been a strange world, according to researchers: very wet in the tropics but with almost nothing growing, researchers said. No forests grew, only shrubs and ferns. No fish or marine reptiles were to be found in the tropics, only shellfish, and virtually no land animals existed because their high metabolic rate made it impossible to deal with the extreme temperatures. Only the polar regions provided a refuge. Before the end-Permian mass extinction the Earth had teemed with plants and animals including primitive reptiles and amphibians, and a wide variety of sea creatures including coral and sea lillies. The broken world scenario is believed to have been caused by a breakdown in global carbon cycling. Normally, plants help regulate temperature by absorbing carbon dioxide and burying it as dead plant matter. Without plants, levels of carbon dioxide can rise unchecked, which causes temperatures to increase. Sun and colleagues collected data from 15,000 ancient conodonts (tiny teeth of extinct eel-like fishes) extracted from two tons of rocks from South China. Conodonts form a skeleton using oxygen. The isotopes, or variants, of oxygen in skeletons are temperature controlled, so by studying the levels in the conodonts he was able to estimate temperature levels hundreds of millions of years ago.