The Sturtian ‘Snowball Earth’ glaciation (717 to 661 million years ago) is regarded as the most extreme interval of icehouse climate in Earth’s history. In a new study, geologists from the University of Sydney and the University of Adelaide have used plate tectonic modeling to determine what most likely caused the Sturtian glaciation.
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An artist’s impression of the ‘Snowball Earth.’ Image credit: Oleg Kuznetsov, http://3depix.com / CC BY-SA 4.0.
“Imagine the Earth almost completely frozen over. That’s just what happened about 700 million years ago,” said lead author Dr. Adriana Dutkiewicz, a researcher at the University of Sydney.
“The planet was blanketed in ice from poles to equator and temperatures plunged. However, just what caused this has been an open question.”
“We 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.”
Named after the 19th century European colonial explorer of central Australia, Charles Sturt, the Sturtian glaciation stretched from 717 to 660 million years ago, a period well before the dinosaurs and complex plant life on land existed.
“Various 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 — a time span hard for us humans to imagine,” Dr. Dutkiewicz said.
Dr. Dutkiewicz and colleagues used 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 carbon dioxide degassing of underwater volcanoes along mid-ocean ridges — the sites where plates diverge and new ocean crust is born.
They soon realized that the start of the Sturtian glaciation precisely correlates with an all-time low in volcanic carbon dioxide emissions.
In addition, the carbon dioxide outflux remained relatively low for the entire duration of the glaciation.
“At this time, there were no multicellular animals or land plants on Earth,” Dr. Dutkiewicz said.
“The greenhouse gas concentration of the atmosphere was almost entirely dictated by carbon dioxide outgassing from volcanoes and by silicate rock weathering processes, which consume carbon dioxide.”
“Geology ruled climate at this time,” said co-author Professor Dietmar Müller, a researcher at the University of Sydney.
“We think the Sturtian ice age kicked in due to a double whammy: a plate tectonic reorganization brought volcanic degassing to a minimum, while simultaneously a continental volcanic province in Canada started eroding away, consuming atmospheric carbon dioxide.”
“The result was that atmospheric carbon dioxide fell to a level where glaciation kicks in — which we estimate to be below 200 parts per million, less than half today’s level.”
The team’s current work raises intriguing questions about Earth’s long-term future.
A recent theory proposed 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 carbon dioxide emissions, as continental collisions increase and the plates slow down.
So, perhaps Pangea Ultima will turn into a snowball again.
“Whatever the future holds, it is important to note that geological climate change, of the type studied here, happens extremely slowly,” Dr. Dutkiewicz said.
“According to NASA, human-induced climate change is happening at a pace 10 times faster than we have seen before.”
The study appears in the journal Geology.
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Adriana Dutkiewicz et al. Duration of Sturtian “Snowball Earth” glaciation linked to exceptionally low mid-ocean ridge outgassing. Geology, published online February 7, 2024; doi: 10.1130/G51669.1
