More than 700 million years ago, Earth experienced one of the most extreme climate events in the planet's history. The entire surface, from the poles to the equator, became covered in ice in what scientists call the Snowball Earth period. Now, researchers using new geological evidence and computer modeling have identified what likely caused this mysterious global freeze that lasted for millions of years.
The discovery comes from multiple studies examining rock formations and using advanced dating techniques. Scientists found physical evidence in Colorado's Rocky Mountains showing that ice sheets reached the equator during this time, confirming that Snowball Earth was truly a global phenomenon. The research also reveals the complex interplay between Earth's geology and climate that created conditions cold enough to freeze the entire planet.
Background
The Snowball Earth period, also known as the Sturtian glaciation, stretched from approximately 717 to 660 million years ago. This was long before dinosaurs walked the Earth or complex plant life existed on land. During this time, glaciers covered the planet from pole to equator, with temperatures plunging to levels that would be unimaginable today.
Geologists have long puzzled over what caused this extreme ice age and, perhaps more mysteriously, why it lasted so long. Various theories have been proposed over the years, but scientists lacked definitive answers about the trigger and the mechanism that kept Earth frozen for 57 million years.
The evidence for Snowball Earth comes from glacial deposits found around the world, including spectacular formations visible in South Australia's Flinders Ranges. These geological markers show signs of ancient glaciation at tropical latitudes, which seemed impossible until the Snowball Earth hypothesis was developed to explain them.
Key Details
The Colorado Discovery
Researchers examining rock formations known as the Tava sandstones in Colorado's Front Range found compelling physical evidence of ice sheet activity at the equator. During the Snowball Earth period, Colorado sat at the equator as part of the ancient supercontinent Laurentia, not at its current northern latitude.
The Tava sandstones contain distinctive geological features called injectites, which form beneath ice sheets. Using a dating technique called laser ablation mass spectrometry, scientists determined that these rocks were pushed underground between 690 and 660 million years ago, right in the middle of Earth's suspected Snowball phase. This provided the first direct physical evidence that ice sheets reached the heart of continents at the equator.
The Double Cause
Australian geologists using computer models to simulate Earth's climate and geology during this period identified what they believe triggered the freeze. The cause was not a single event but rather a combination of two major factors happening at the same time.
First, a reorganization of Earth's plate tectonics brought volcanic activity to historic lows. Volcanoes, which normally release carbon dioxide into the atmosphere, were releasing far less of this greenhouse gas than usual. Second, a large volcanic rock formation in what is now Canada began to weather and erode. This weathering process consumed atmospheric carbon dioxide, removing it from the air.
"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 carbon dioxide," said Professor Dietmar Müller from the University of Sydney.
The combined effect was dramatic. Atmospheric carbon dioxide levels fell below 200 parts per million, less than half of today's levels. At these low concentrations, Earth's climate tipped into glaciation, and ice sheets began spreading across the planet.
Why It Lasted So Long
Once the ice covered the planet, it created a self-reinforcing cycle. Ice reflects sunlight back into space more effectively than water or rock, which meant less heat was absorbed by the planet. This kept temperatures cold enough to maintain the ice sheets. The low volcanic carbon dioxide emissions remained low throughout the entire 57-million-year period, preventing the atmosphere from warming enough to melt the ice.
Eventually, the plate tectonic reorganization changed again, volcanic activity increased, and carbon dioxide levels rose. This gradual warming finally broke the freeze, allowing the ice to melt and life to flourish in the oceans.
What This Means
Understanding Snowball Earth helps scientists grasp how sensitive Earth's climate is to atmospheric carbon dioxide levels and how geological processes shape climate over millions of years. The research shows that Earth has a built-in thermostat, but it operates on timescales that are almost incomprehensible to humans.
The timing of Snowball Earth's end is particularly significant for the history of life. The first multicellular organisms, ancestors of modern animals and plants, emerged in the oceans shortly after the ice melted. The extreme conditions of Snowball Earth and the dramatic changes that followed appear to have played a role in spurring major evolutionary transitions.
The research also raises questions about Earth's distant future. Some scientists have theorized that over the next 250 million years, Earth could evolve into a supercontinent called Pangea Ultima. Understanding how geological processes have shaped climate in the past may help predict how they could affect the planet's climate millions of years from now.
