Australian geologists used plate tectonic models to determine the most likely cause of Earth's extreme ice age climate more than 700 million years ago. Volcanic carbon emissions reached an all-time low, triggering a global ice age that lasted 57 million years. The research, published in Geology, helps us understand the function of Earth's built-in thermostat, which prevents it from slipping into overheating mode. It also shows how sensitive global climate is to atmospheric carbon concentrations.

Australian geologists have discovered that low volcanic carbon dioxide emissions and rock weathering in Canada were key factors behind an extreme ice age 700 million years ago. Their research draws on plate tectonic models and geological evidence from South Australia to reveal the Earth's climate sensitivity and its natural thermostatic mechanism, contrasting the slow pace of geological climate change with the rapid changes driven by human activity. Source: NASA

Dr Adriana Dutkiewicz, lead author of the study and ARC Future Fellow, said: "Imagine the Earth was almost completely covered in ice and snow. This is what happened about 700 million years ago; the Earth was covered in ice and snow from the poles to the equator, and temperatures plummeted. However, exactly what caused this has been an open question."

The Sturt Formation glacial deposits in the northern part of Australia's Flinders Ranges near the Arkaroola Wilderness Sanctuary are approximately 717-66.4 billion years old. Study lead author Dr Adriana Dutkiewicz from the University of Sydney's School of Earth Sciences points to the thick layer of glacial deposits. Image credit: Professor Dietmar Müller/University of Sydney

"We now think we have cracked the mystery: Historically low volcanic CO2 emissions are due to the weathering of a large mass of volcanic rocks now in Canada; a process that absorbs atmospheric CO2."

The project was inspired by the spectacular glacial debris left behind by ancient glaciers from this period, which can be seen in the Flinders Ranges of South Australia.

A recent geological field trip to the mountains, led by co-author Professor Alan Collins of the University of Adelaide, prompted the team to use the University of Sydney's EarthByte computer model to study the origins and duration of this glacial period.

From 717 million years ago to 660 million years ago, the earth was covered with ice and snow - an ice age that lasted 57 million years. University of Sydney geoscientists led by Dr Adriana Dutkiewicz and Professor Dietmar Müller have identified a possible cause: volcanic carbon dioxide levels in the atmosphere have reached record lows. This video shows the movement of continents (gray) and plate boundaries (orange) from 850 million years ago to 540 million years ago (snowflakes appeared during the "Snowball Earth" period). Image source: Ben Mather and Dietmar Müller/University of Sydney

The extended ice age, also known as the Stewart Glaciation, named after Charles Stewart, the 19th-century European explorer of central Australia, lasted from 717 to 660 million years ago, long before the emergence of dinosaurs and complex plant life on land.

Dr Dutkiewicz said: "Various reasons have been proposed for the triggering and ending of this extreme ice age, but the most mysterious is why it lasted 57 million years - a time span that we humans can hardly imagine."

The team returned to plate tectonic models, which show the evolution of continents and ocean basins following the breakup of the ancient supercontinent Rodina. They connected this to a computer model that calculated carbon dioxide degassing from underwater volcanoes along mid-ocean ridges, where plates diverge and new ocean crust is born.

Dr Adriana Dutkiewicz from the School of Earth Sciences, University of Sydney, Flinders Ranges, South Australia. Source: University of Sydney

They soon realized that the start of the Stewart Ice Age coincided with an all-time low in volcanic carbon dioxide emissions. Furthermore, the outflow of carbon dioxide remained relatively low throughout the ice age.

Dr Dutkiewicz said: "At this time, there were no multicellular animals or land plants on Earth. The concentration of greenhouse gases in the atmosphere was almost entirely determined by carbon dioxide emitted by volcanoes and the weathering process of silicate rocks, which consumes carbon dioxide."

Co-author Professor Dietmar Müller from the University of Sydney said: "Geology dominated climate during this period. We believe that the onset of the Stewart Ice Age was the result of a double whammy: plate tectonic reorganization that minimized volcanic degassing, while Canada's continental volcanic areas began to erode, depleting carbon dioxide from the atmosphere."

A view from the Flinders Ranges towards the Akalura Wilderness Reserve. Glacial deposits in the Stewart Formation formed by the Stewart Glaciation approximately 717-664 million years ago form a prominent ridge in the center left of the photo. Image credit: Professor Dietmar Müller/University of Sydney

"As a result, atmospheric carbon dioxide dropped to levels seen at the beginning of the Ice Age - which we estimate to be below 200 parts per million, less than half of today's levels."

The research team's work raises interesting questions about Earth's long-term future. A recent theory proposes that over the next 250 million years, Earth will evolve toward Pangea Ultima, a supercontinent with temperatures so high that mammals may become extinct.

However, Earth is also now on a trajectory for lower volcanic carbon dioxide emissions as continental collisions intensify and plate velocities slow. So maybe "Pangia Ultimate" will snowball again.

Dr Dutkiewicz said: "Whatever happens in the future, it is important to note that the geological climate changes studied here occur extremely slowly. According to NASA, the rate of human-induced climate change is 10 times faster than what we have seen before."

Compiled source: ScitechDaily