What made Earth a giant snowball 700m years ago? Scientists have an answer
Deposits from the Sturtian Glaciation 717颅鈥�664 million years ago in the northern Flinders Ranges, Australia. Research lead author Dr Adriana Dutkiewicz pointing to a thick bed of glacial deposits. 聽Photo: Professor Dietmar M眉ller/University of Sydney
Australian geologists have used plate tectonic modelling to determine what most likely caused an extreme ice-age climate in Earth鈥檚 history, more than 700 million years ago.
The study, published in , helps our understanding of the functioning of the Earth's built-in thermostat that prevents the Earth from getting stuck in overheating mode. It also shows how sensitive global climate is to atmospheric carbon concentration.
鈥淚magine the Earth almost completely frozen over,鈥� said the study鈥檚 lead author, ARC Future Fellow . 鈥淭hat鈥檚 just what happened about 700 million years ago; the planet was blanketed in ice from poles to equator and temperatures plunged. However, just what caused this has been an open question.
鈥淲e now think we have cracked the mystery: historically low volcanic carbon dioxide emissions, aided by weathering of a large pile of volcanic rocks in what is now Canada; a process that absorbs atmospheric carbon dioxide.鈥�
The project was inspired by the glacial debris left by the ancient glaciation from this period that can be spectacularly observed in the Flinders Ranges in South Australia.
A recent geological field trip to the Ranges, led by co-author from the University of Adelaide, prompted the team to use the University of Sydney computer models to investigate the cause and the exceptionally long duration of this ice age.
The extended ice age, also called the Sturtian glaciation after the 19th century European colonial explorer of central Australia, Charles Sturt, stretched from 717 to 660 million years ago, a period well before the dinosaurs and complex plant life on land existed.
Plate tectonics during Sturtian ice age
Credit: Ben Mather and Dietmar M眉ller
Dr Dutkiewicz said: 鈥淰arious causes have been proposed for the trigger and the end of this extreme ice age, but the most mysterious aspect is why it lasted for 57 million years 鈥� a time span hard for us humans to imagine.鈥�
The team went back to a plate tectonic model that shows the evolution of continents and ocean basins at a time after the breakup of the ancient supercontinent Rodina. They connected it to a computer model that calculates CO2聽degassing of underwater volcanoes along mid-ocean ridges 鈥� the sites where plates diverge and new ocean crust is born.
They soon realised that the start of the Sturtian ice age precisely correlates with an all-time low in volcanic CO2聽emissions. In addition, the CO2聽outflux remained relatively low for the entire duration of the ice age.
Dr Dutkiewicz said: 鈥淎t this time, there were no multicellular animals or land聽plants on Earth. The greenhouse gas concentration of the atmosphere was almost entirely dictated by CO2聽outgassing from volcanoes and by silicate rock weathering processes, which consume CO2.鈥�
Professor Dietmar M眉ller points to carbonates overlying glacial deposits in the Flinders Ranges. Photo: Dr Adriana Dutkiewicz
颁辞-补耻迟丑辞谤听Professor Dietmar M眉ller聽from the University of Sydney said: "Geology ruled climate at this time. We think the Sturtian ice age kicked in due to a double whammy: a plate tectonic reorganisation brought volcanic degassing to a minimum, while simultaneously a continental volcanic province in Canada started eroding away, consuming atmospheric CO2.
鈥淭he result was that atmospheric CO2聽fell to a level where glaciation kicks in 鈥� which we estimate to be below 200 parts per million, less than half today鈥檚 level.鈥�
The team's work raises intriguing questions about Earth's long-term future.聽 A聽聽that over the next 250 million years, Earth would evolve towards Pangea Ultima, a supercontinent so hot that mammals might become extinct.
However, the Earth is also currently on a trajectory of lower volcanic CO2聽emissions, as continental collisions increase and the plates slow down. So, perhaps Pangea Ultima will turn into a snowball again.
Dr Dutkiewicz said: 鈥淲hatever the future holds, it is important to note that geological climate change, of the type studied here, happens extremely slowly.聽, human-induced climate change is happening at a pace 10 times faster than we have seen before.鈥�
Research
鈥楧uration of Sturtian 鈥淪nowball Earth鈥� glaciation linked to exceptionally low mid-ocean ridge outgassing鈥�, Dutkiewicz, A. et al (Geology, 2024). DOI: 10.1130/G51669.1
EarthByte Group
This work was enabled by the聽聽plate tectonic software, developed by the聽聽at the University of Sydney, which has been the basis of a slew of discoveries over the past decade, contributing significant knowledge to how geology is a central long-term driver of climate and biodiversity. GPlates development is supported by the AuScope National Collaborative Research Infrastructure System (NCRIS) program.
Declaration
The authors declare no competing interests. Research was in part funded by the Australian Research Council.