The team, led by scientists from Harvard University, studied rocks collected in Canada’s remote Yukon Territory that were located in tropical latitudes 716.5 million years ago, when the Earth was in the grip of the so-called Sturtian glaciation. Some geologists believe that this ice age encompassed the entire planet, leading to a so-called ‘snowball Earth’ scenario.

The rocks contained glacial deposits, as well as other signs of glaciation, such as striated clasts (fragments of rock with grooves worn into them), ice-rafted debris and deformation of soft sediments. Using the magnetic qualities and composition of the samples, the geologists were able to determine that 716.5 million years ago, they were located at sea level in the tropics, at about 10 latitude. 

‘This is the first time that the Sturtian glaciation has been shown to have occurred at tropical latitudes, providing direct evidence that this particular glaciation was a snowball Earth event, said the study’s lead author, Francis Macdonald. ‘Our data also suggest that the Sturtian glaciation lasted for a minimum of five million years.’

May 2010