Testing the snowball Earth hypothesis for the Ediacaran
Alexei V. Ivanov et al., Institute of the Earth's Crust, Siberian Branch, Russian Academy of Sciences, Lermontov Street 128, Irkutsk 664033, Russia. Posted online ahead of print 16 May 2013; http://dx.doi.org/10.1130/G34345.1.
Earth experienced ultimately cold climates several times in its history, such as glaciers reaching the tropical latitudes, and the ocean probably stayed completely frozen. This type of climate stage is known as snowball Earth. Siberia was once tropical during the Ediacaran period about 580-570 million years ago, yet it was glaciated. If Earth was at the snowball stage and thus completely covered by ice, the ice prevented accumulation of cosmic dust and micrometeorites at oceanic floor. The dust and micrometeorite particles would have accumulated rapidly on the ocean floor at the ice-melting event, providing a geochemical signal. However, unlike a previous Cryogenian glaciation at about 635 million years ago, which is a classic example of the snowball Earth conditions, Alexei Ivanov and colleagues find this signal to be at a background level, suggesting that Ediacaran glaciation recorded in Siberia did not reach the snowball Earth stage. The severe cold climate and open oceans probably were prerequisites for evolution of metazoan and a later burst of life on Earth.
Evidence for extensive methane venting on the southeastern U.S. Atlantic margin
L.L. Brothers et al., U.S. Geological Survey, 384 Woods Hole Road, Woods Hole, Massachusetts 02543, USA. Posted onl
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