New Insight Into The Origins Of The Snowball Earth Event

Dropstones, lumps of rock embedded within a different type of stone
(usually igneous or metamorphic within sedimentary), are some of the
most reliable pieces of evidence for the global glaciation known as the
 Snowball Earth Event

800 million years ago, the Earth began to cool. Vast glaciers advanced from the poles, encircling our planet in sheets of ice many miles thick. Temperatures plummeted. Life nearly died out. Yet it was after this single destructive event that complex, multicellular life forms evolved, eventually to become a dominant force, building mountains and draining rivers. The real mystery lies in the fact that geologists have still not synthesised any solid reasons for the sudden global ice age.

Rock formations across the Earth have been studied, samples analysed and the data plotted, but after decades of research, no definitive solutions have presented themselves. However there is a different approach to solving the mysteries of the past. It is the inverse of such methods presented above. Instead of trying to find the way something may have happened, the focus is on what did not happen.

For some time, geochemists and palaeoclimatologists the world over believed that a fluctuation in the carbon cycle around 800 billion years ago was responsible for the extreme change in the Earth's climate. A group of scientists from the University of Miami Rosenstiel School of Marine and Atmospheric Science, led by Professor Peter Swart, decided that they would test this theory. The problem with studying events so far back is that most of the geological evidence has been destroyed over time by the movement of continents.

In order to study the way the carbon cycle changes just before a glaciation event, the researchers chose an ice age that is just within living memory: a time when mammoths roamed the Earth and humans were not just one of a kind. They took cores of carbonates from Pliocene and Pleistocene rock formations from the Bahamas and Enewatak Atoll in the Pacific Ocean and analysed the ratios of the rare carbon-13 to the more common carbon-12.

The pattern of change was identical to the scantily recorded version in rocks dating to just before the Snowball Earth Event. The only surprising piece of data was that the change in the Pliocene-Pleistocene rocks was due to particles brought in by freshwater. Swart believes that the same anomaly was responsible for chemical composition of the 800 million year old rocks. As the water froze, the changes in the water would have led to the isotopic variations.

This led him to the conclusion that fluctuations in the carbon cycle were not responsible for the glaciation.'It is widely accepted that changes in the carbon isotopic ratio during the Pliocene-Pleistocene time are the result of alteration of rocks by freshwater' said Swart. 'We believe this is also what occurred during the Neoproterozoic. Instead of being related to massive and complicated changes in the carbon cycle, the variations seen in the Neoproterozoic can be explained by a simple process which we understand very well.'