Earth was a giant snowball 700 million years ago, now scientists know why – Earth.com

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Australian geologists have shared new findings on an extreme ice-age event that enveloped Earth in a snowball over 700 million years ago, a period marked by a planet-wide glacial cover extending from the poles to the equator.

This fascinating research from a group of scientists at the University of Sydney deepens our comprehension of Earth’s natural temperature regulation mechanisms, while highlighting the delicate balance of our planet’s climate in response to shifts in atmospheric carbon dioxide levels.

Under the ice of “Snowball Earth”

Dr. Adriana Dutkiewicz, the study’s lead author and ARC Future Fellow, paints a vivid picture of this ancient freeze, which has come to be known as “Snowball Earth.”

“Imagine the Earth almost completely frozen over,” explained Dr Dutkiewicz. “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.”

A recent geological field trip to the Ranges, under the leadership of co-author Professor Alan Collins from the University of Adelaide, inspired the team to employ the University of Sydney EarthByte computer models for probing the cause and the remarkably prolonged duration of this ice age.

Named after Charles Sturt, the 19th-century European colonial explorer of central Australia, the Sturtian glaciation spanned from 717 to 660 million years ago.

This period, occurring long before the emergence of dinosaurs and complex terrestrial plant life, marks a significant epoch in Earth’s prehistoric timeline.

Sturtian glaciation: A deep dive

They propose a compelling theory: the ice age, known as the Sturtian glaciation, was primarily triggered by historically low volcanic carbon dioxide emissions, compounded by the weathering of volcanic rock in present-day Canada, which absorbed atmospheric CO2.

“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,” said Dr Dutkiewicz.

The significance of this glaciation, stretching from 717 to 660 million years ago, cannot be overstated. Occurring well before the age of dinosaurs and complex terrestrial plant life, it represents a pivotal epoch in Earth’s history.

Dr. Dutkiewicz explains, “Various factors have been considered for the initiation and conclusion of this ice age, but its remarkable duration of 57 million years has been especially baffling.”

Many different geological forces at play

The research team’s investigations reveal a correlation between the onset of the Sturtian glaciation and a dramatic reduction in volcanic CO2 emissions. This condition persisted throughout the “Snowball Earth” ice age.

The team created a demonstration video that can be found here.

This period was characterized by an absence of multicellular animals and land plants, with greenhouse gas levels predominantly influenced by volcanic activity and silicate rock weathering.

Professor Dietmar Müller, a co-author from the University of Sydney, emphasizes the geological dominance over climate during this era, noting a “double whammy” effect.

During this “Snowball Earth” period, a reconfiguration of plate tectonics reduced volcanic degassing to a minimum, while erosion of a volcanic region in Canada led to significant CO2 absorption.

“Geology ruled climate at this time. The result was that atmospheric CO2 fell to a level where glaciation kicks in — which we estimate to be below 200 parts per million, less than half today’s level,” Müller explained.

The resulting drop in atmospheric CO2, estimated to fall below 200 parts per million, was critical for glaciation onset, marking a stark contrast to today’s levels.

An ice age in Earth’s future?

In summary, this study resolves a longstanding mystery and prompts contemplation about Earth’s distant future.

While a theory suggests the formation of a swelteringly hot supercontinent, Pangea Ultima, within the next 250 million years, current trends of diminishing volcanic CO2 emissions could hint at another potential ice age.

Dr. Dutkiewicz cautions, however, that geological climate shifts occur over vast timescales, contrasting sharply with the rapid pace of human-induced climate change.

“Whatever the future holds, it is important to note that geological climate change, of the type studied here, happens extremely slowly,” said Dr. Dutkiewicz. “According to NASA, human-induced climate change is happening at a pace 10 times faster than we have seen before.”

By connecting past events with future possibilities, this research underscores the intricate interplay between geological processes and climate dynamics, offering a lens through which to view both Earth’s ancient past and its unfolding future.

The full study was published in the journal Geology.

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