Environment Counts | New evidence supports “snowball Earth” hypothesis :

Published by on Tuesday, January 24th, 2017

Published
by geoff
on 2015-04-24

The controversial snowball Earth hypothesis posits that more than 600 million years ago before the appearance of multi-cellular life forms on Earth, the Earth’s surface became entirely frozen at least once. Classic paleo-thermometers such as oxygen-18/oxygen-16 ratios in marine carbonates are not available for snowball Earth episodes. The authors present the results of a novel approach to reconstruct the oxygen-18/oxygen-16 composition of ancient water from precipitation (rain and snow) using the triple oxygen isotopic composition, oxygen-17/oxygen-16 and oxygen-18/oxygen-16 ratios, of rocks chemically altered by high temperature and pressure in the presence of water. The oxygen-18/oxygen-16 composition calculated from waters found at latitudes near the equator during a suspected snowball Earth episode 2.4 billion years ago are extremely low and correspond to oxygen-18/oxygen-16 compositions observed in the present era only in central Antarctica where current temperatures average -30 Â°C in summer and -60 Â°C in winter. Daniel Herwartz, doi: 10.1073/pnas.1422887112

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