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Extreme Cli­mate Change Linked To Early Ani­mal Evolution

pub­lished 28 Sep­tem­ber 2012 | mod­i­fied 04 Decem­ber 2012

Uni­ver­sity of Cal­i­for­nia (UC) River­side geo­sci­en­tists help tie spike in ancient oceanic oxy­gen lev­els to ‘Snow­ball Earth’ event

Doushantuo FormationAn inter­na­tional team of sci­en­tists, includ­ing geo­chemists from the UC River­side, has uncov­ered new evi­dence link­ing extreme cli­mate change, oxy­gen rise, and early ani­mal evo­lu­tion. A dra­matic rise in atmos­pheric oxy­gen lev­els has long been spec­u­lated as the trig­ger for early ani­mal evo­lu­tion. While the direct cause-​and-​effect rela­tion­ships between ani­mal and envi­ron­men­tal evo­lu­tion remain top­ics of intense debate, all this research has been ham­pered by the lack of direct evi­dence for an oxy­gen increase coin­ci­dent with the appear­ance of the ear­li­est ani­mals — until now.

In the Sep­tem­ber 27 issue of the jour­nal Nature, the research team, led by sci­en­tists at the Uni­ver­sity of Nevada, Las Vegas, offers the first evi­dence of a direct link between trends in early ani­mal diver­sity and shifts in Earth sys­tem processes. The fos­sil record shows a marked increase in ani­mal and algae fos­sils roughly 635 mil­lion years ago. An analy­sis of organic-​rich rocks from South China points to a sud­den spike in oceanic oxy­gen lev­els at this time — in the wake of severe glacia­tion. The new evi­dence pre-​dates pre­vi­ous esti­mates of a life-​sustaining oxy­gena­tion event by more than 50 mil­lion years.

This work pro­vides the first real evi­dence for a long spec­u­lated change in oxy­gen lev­els in the after­math of the most severe cli­matic event in Earth’s his­tory — one of the so-​called ‘Snow­ball Earth’ glaciations
Tim­o­thy Lyons, a pro­fes­sor of bio­geo­chem­istry at UC River­side »

The research team analysed con­cen­tra­tions of trace met­als and sul­fur iso­topes, which are trac­ers of early oxy­gen lev­els, in mud­stone col­lected from the Doushan­tuo For­ma­tion in South China. The team found spikes in con­cen­tra­tions of the trace met­als, denot­ing higher oxy­gen lev­els in sea­wa­ter on a global scale. “We found lev­els of molyb­de­num and vana­dium in the Doushan­tuo For­ma­tion mud­stones that neces­si­tate that the global ocean was well ven­ti­lated. This well-​oxygenated ocean was the envi­ron­men­tal back­drop for early ani­mal diver­si­fi­ca­tion,” said Noah Planavsky, a for­mer UC River­side grad­u­ate stu­dent in Lyons’s lab now at Cal­Tech.

The high ele­ment con­cen­tra­tions found in the South China rocks are com­pa­ra­ble to mod­ern ocean sed­i­ments and point to a sub­stan­tial oxy­gen increase in the ocean-​atmosphere sys­tem around 635 mil­lion years ago. Accord­ing to the researchers, the oxy­gen rise is likely due to increased organic car­bon bur­ial, a result of more nutri­ent avail­abil­ity fol­low­ing the extreme cold cli­mate of the ‘Snow­ball Earth’ glacia­tion when ice shrouded much of Earth’s sur­face.

Lyons and Planavsky argued in research pub­lished ear­lier in the jour­nal Nature that a nutri­ent sur­plus asso­ci­ated with the exten­sive glacia­tions may have ini­ti­ated intense car­bon bur­ial and oxy­gena­tion. Bur­ial of organic car­bon — from pho­to­syn­thetic organ­isms — in ocean sed­i­ments would result in the release of vast amounts of oxy­gen into the ocean-​atmosphere sys­tem.

We are delighted that the new metal data from the South China shale seem to be con­firm­ing these hypoth­e­sized events
(Tim­o­thy Lyons)

The above news item is reprinted from mate­ri­als avail­able at Uni­ver­sity of Cal­i­for­nia, River­side. Orig­i­nal text may be edited for con­tent and length.

(Source: UC River­side Today, 26.09.2012)

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