Sturtian glaciation

The Sturtian glaciation was a massive, global cooling event. It occurred during the Cryogenian Period of Earth's history. This event is one of the most significant in our planet's past. It is considered the longest and most severe glacial event in the geologic record, following the much earlier Huronian glaciation. Scientists debate exactly how cold the planet became. Some hypothesize it was a Snowball Earth event. This theory suggests ice may have covered the entire globe. Others suggest it consisted of multiple regional glaciations.

Geologists study this period by looking at specific rock sequences. The Sturtian succession includes two major diamictite-mudstone sequences. Diamictite is a type of rock formed from unsorted sediment. These sequences represent cycles of glacial advance and retreat. An advance occurs when ice sheets grow and move forward. A retreat occurs when the ice melts and moves back. These rocks show how the climate shifted over long periods. In North America, this succession is correlated with the Rapitan Group.

Evidence of this glaciation is found on every single continent. Notable geological sections exist in Australia, Canada, China, and Ethiopia. You can also find evidence in Namibia, Siberia, and Svalbard. In northern Norway, a feature called Reusch's Moraine may have formed during this time. In Australia, the Sturtian glaciogenic succession sits unconformably over the Burra Group. This means there is a gap in the rock record between them. The ice sheet advance at the start of the glaciation lasted less than one million years.

The name for this period comes from the Sturt Formation. This formation is located within the Adelaide Superbasin in Australia. The name honors Sturt Gorge and the Sturt River. Captain Collet Barker named the river in April 1831. He named it after the explorer Charles Sturt. In 1950, Douglas Mawson and Reg Sprigg defined the term. They originally used it as a chronostratigraphic unit. This helped researchers study the Neoproterozoic era. This research eventually led to the Snowball Earth hypothesis.

Scientists are still discovering why this glaciation happened. In 2024, researchers from the University of Adelaide and University of Sydney proposed a new idea. They used plate tectonic modelling and EarthByte computer models. They believe the extreme cold resulted from the break-up of a supercontinent called Rodinia. As Rodinia broke apart, it changed the activity at mid-ocean ridges. This led to low levels of degassing. Degassing is the process where gases are released from the Earth's interior. This reduction in gases likely caused the drop in temperature.

The timing of this event is very specific. The Sturtian glaciation lasted for approximately 57 million years. It is thought to have begun around 717 Ma. It lasted until about 660 Ma. The "Ma" stands for millions of years ago. This was the older of two worldwide glacial events in the Cryogenian. The other event is known as the Marinoan or Elatina glaciation. Understanding these exact dates helps scientists map the history of Earth's climate.

This period of ice had a profound effect on life. Although the ice was severe, life continued to change. In the aftermath of the glaciation, scientists found new clues. They identified biomarkers, which are chemical signatures of life. They also found body fossils. These biological clues indicate an increase in biological complexity. This means that life became more intricate and varied after the ice melted. The transition from the Sturtian glaciation helped shape the future of biological evolution on Earth.