Mystery solved: Why Earth became a frozen planet 700 million years ago

Geologists in Australia have uncovered a chilling discovery about Earth's ancient past, shedding light on a mystery that puzzled scientists for years. Their research, recently published in the journal Geology, delves into the extreme ice-age climate that gripped the planet over 700 million years ago.

Lead author of the study, Dr. Adriana Dutkiewicz, an ARC Future Fellow, paints a vivid picture of this icy epoch, stating, "Imagine the Earth almost completely frozen over. That's 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."

The investigation was sparked by the remarkable glacial remnants found in the Flinders Ranges of South Australia, a testament to Earth's ancient climatic upheavals. Co-author Professor Alan Collins from the University of Adelaide led a geological field trip to the region, inspiring the team to unravel the mysteries of this prolonged ice age.

Known as the Sturtian glaciation, this icy period endured from 717 to 660 million years ago, predating the existence of dinosaurs and complex land plants. Dr. Dutkiewicz remarks, "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."

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To decipher the puzzle, the team turned to sophisticated plate tectonic models and computer simulations. They linked the breakup of the ancient supercontinent Rodina to volcanic CO2 emissions along mid-ocean ridges, where new ocean crust forms.

Their analysis revealed a crucial correlation: the onset of the Sturtian ice age coincided with a historic low in volcanic CO2 emissions. Moreover, this reduced CO2 outflux persisted throughout the entirety of the ice age.

Professor Dietmar Müller from the University of Sydney emphasizes the geological dominance over climate during this era, stating, "Geology ruled climate at this time." The team's findings suggest a dual mechanism driving the ice age: a decline in volcanic CO2 emissions due to tectonic reorganization, coupled with extensive erosion of continental volcanic rocks in Canada, which consumed atmospheric CO2.

This double whammy led to a drastic drop in atmospheric CO2 levels, triggering glaciation when concentrations fell below 200 parts per million—less than half of today's levels.

The implications of this research extend beyond Earth's ancient history. It prompts speculation about the planet's future trajectory, particularly in light of theories proposing the eventual formation of a supercontinent dubbed Pangea Ultima.

According to Dr. Dutkiewicz, "The Earth is currently on a trajectory of lower volcanic CO2 emissions, as continental collisions increase and the plates slow down." This raises the intriguing possibility that Pangea Ultima might veer towards another ice age scenario.

However, Dr. Dutkiewicz is quick to caution against drawing direct parallels to the present. She emphasizes the glacial pace of geological climate change compared to the rapidity of human-induced climate change, as highlighted by NASA.

As we contemplate Earth's future, it underscores the complex interplay between tectonics, volcanic activity, and atmospheric carbon levels—an intricate dance that has shaped our planet's climate over millions of years.

Study information: Adriana Dutkiewicz et al, Duration of Sturtian "Snowball Earth" glaciation linked to exceptionally low mid-ocean ridge outgassing, Geology (2024). DOI: 10.1130/G51669.1

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