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Did a modern-day scourge save ancient Earth?

Nov. 30, 2008
Courtesy Imperial College London
and World Science staff

Our planet’s pre­s­ent-day “green­house” scourge, car­bon di­ox­ide, may have helped an­cient Earth es­cape a deep freeze, some U.K. sci­en­tists pro­pose.

The re­search­ers claim Earth nev­er froze over com­pletely dur­ing the so-called Cryo­ge­nian per­i­od, about 840 to 635 mil­lion years ago. This view con­tra­dicts the “Snow­ball Earth” hy­poth­e­sis, which claims Earth was locked in ice for many mil­lions of years ow­ing to a run­away, plan­et-cooling chain re­ac­tion.

The Snowball Earth hy­po­the­sis pro­poses a severe plan­etary gla­ci­a­tion dur­ing part of the Earth's Pre­cam­b­rian era, when some of the most prim­i­tive life forms arose.
What might have let the plan­et es­cape this fate is un­clear, but the sci­en­tists point to re­cent re­search from the Uni­ver­s­ity of To­ron­to. This spec­u­lates that ad­vanc­ing ice was stalled by the in­ter­ac­tion of the cli­mate sys­tem and the car­bon cy­cle of the ocean, with car­bon di­ox­ide play­ing a key role in in­su­lat­ing the plan­et. 

Car­bon di­ox­ide is by the same to­ken to­day blamed for glob­al warm­ing.

The To­ron­to sci­en­tists say that as Earth’s tem­per­a­tures cooled, ox­y­gen was drawn in­to the ocean, where it re­acted chem­ic­ally with or­gan­ic mat­ter, re­leas­ing car­bon di­ox­ide in­to the at­mos­phere.

Some­thing must have kept the plan­et’s equa­to­ri­al oceans from freez­ing over, said geo­sci­en­tist Phil­lip Al­len of Im­pe­ri­al Col­lege Lon­don, who with col­leagues pre­sented the new pro­pos­al in a pa­per pub­lished on­line Nov. 30 in the re­search jour­nal Na­ture Ge­o­sci­ence.

“In the cli­mate change game, car­bon di­ox­ide can be both saint and sin­ner. These days we are so con­cerned about glob­al warm­ing and the harm that car­bon di­ox­ide is do­ing to our plan­et. How­ev­er, ap­prox­i­mately 600 mil­lion years ago, this green­house gas probably saved an­cient Earth and its bas­ic life forms from an icy ex­tinc­tion.”

Al­len, whose pre­vi­ous re­search has found ev­i­dence of hot and cold cy­cles in the Cryo­ge­nian per­i­od, said many pa­pers have been pub­lished and much de­bate de­vot­ed to the Snow­ball Earth the­o­ry.

“Sed­i­men­tary rocks de­posited dur­ing these cold in­ter­vals in­di­cate that dy­nam­ic glaciers and ice streams con­tin­ued to de­liv­er large amounts of sed­i­ment to open oceans. This ev­i­dence con­tra­dicts the Snow­ball Earth the­o­ry, which sug­gests the oceans were fro­zen over. Yet, many sci­en­tists still be­lieve Snow­ball Earth to be cor­rect.”

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Earth’s present-day “greenhouse” scourge, carbon dioxide, may have helped ancient Earth escape a deep freeze, some U.K. scientists propose. The researchers claim Earth never froze over completely during the Cryogenian Period, about 840 to 635 million years ago. This view contradicts the Snowball Earth hypothesis, which claims Earth was locked in ice for many millions of years owing to a runaway, planet-cooling chain reaction. What might have let the planet escape this fate is unclear, but the scientists point to recent research from the University of Toronto. This speculates that the advancing ice was stalled by the interaction of the climate system and the carbon cycle of the ocean, with carbon dioxide playing a key role in insulating the planet. Carbon dioxide is by the same token today blamed for global warming. The Toronto scientists say that as Earth’s temperatures cooled, oxygen was drawn into the ocean, where it reacted chemically with organic matter, releasing carbon dioxide into the atmosphere. Something must have kept the planet’s equatorial oceans from freezing over, said geoscientist Phillip Allen of Imperial College London, who with colleagues presented the new proposal in a paper published online Nov. 30 in the research journal Nature Geoscience. “In the climate change game, carbon dioxide can be both saint and sinner. These days we are so concerned about global warming and the harm that carbon dioxide is doing to our planet. However, approximately 600 million years ago, this greenhouse gas probably saved ancient Earth and its basic life forms from an icy extinction.” Allen, whose previous research has found evidence of hot and cold cycles in the Cryogenian period, said many papers have been published and much debate devoted to the Snowball Earth theory. “Sedimentary rocks deposited during these cold intervals indicate that dynamic glaciers and ice streams continued to deliver large amounts of sediment to open oceans. This evidence contradicts the Snowball Earth theory, which suggests the oceans were frozen over. Yet, many scientists still believe Snowball Earth to be correct.”