Geologists discover new evidence of Snowball Earth 700 million years ago

Around 700 million years ago, Earth experienced a climate catastrophe so severe that ice sheets covered the planet from pole to equator. Known as the Snowball Earth hypothesis, this theory suggests that from 720 to 635 million years ago, our planet became an ice-bound sphere.

For decades, geologists have debated whether this global freeze extended to the heart of continents, particularly those near the equator. Now, new research from the University of Colorado Boulder offers compelling evidence that it did.

In a groundbreaking study, researchers examined formations known as the Tavakaiv, or "Tava," sandstones in Colorado’s Rocky Mountains. These rocks hold clues to a frigid chapter in Earth's history.

Liam Courtney-Davies, the study's lead author, describes the research as a pivotal step in confirming Snowball Earth’s reach. "This study presents the first physical evidence that Snowball Earth reached the heart of continents at the equator," he said.

The study, published in the Proceedings of the National Academy of Sciences, involved geologists from institutions including Colorado College, the University of California, and CU Boulder.

Their work centered on sandstone injectites, vertical rock formations that poke through the Colorado landscape. These structures, formed under extreme pressure, offer a snapshot of geological upheaval during the Cryogenian period, which spanned 720 to 635 million years ago.

Using a technique called laser ablation mass spectrometry, researchers analyzed mineral veins within the Tava sandstones. This method uses lasers to release atoms from minerals, allowing scientists to measure the decay of uranium to lead. The results dated the sandstones’ formation to approximately 690 to 660 million years ago—a timeline aligning with Snowball Earth.

Courtney-Davies explains the significance: “These are classic geological features called injectites that often form below some ice sheets, including in modern-day Antarctica.”

During this time, the region that is now Colorado sat near the equator, as part of the ancient supercontinent Laurentia. Unlike its current mountainous terrain, Colorado was a flat, landlocked area. If massive glaciers formed here, they likely did so elsewhere along equatorial regions.

The researchers believe thick ice sheets pressed down on Colorado's surface, pushing the Tava sandstones deep underground. This pressure would have forced the sands into bedrock, creating the injectites seen today.

Fieldwork and analysis also revealed signs of glacial loading, fluid overpressure, and repeated sand injections caused by meltwater events—processes that mimic modern glacial dynamics in Antarctica.

The Snowball Earth hypothesis has fascinated scientists since American geologist Joseph Kirschvink introduced the term in 1992. It describes a planet-wide freeze where ice covered not only oceans but land masses as well. While evidence of glaciation has been found in coastal regions, proof from continental interiors has remained elusive.

The Colorado study changes that. Rebecca Flowers, co-author and professor of geological sciences at CU Boulder, emphasizes its importance: "We're excited that we had the opportunity to unravel the story of the only Snowball Earth deposits that have so far been identified in Colorado.”

This discovery also sheds light on how life might have evolved during and after Snowball Earth. The thaw that followed this icy era is believed to have triggered the emergence of the first multicellular organisms. "You have the climate evolving, and you have life evolving with it," Courtney-Davies said. "All of these things happened during Snowball Earth upheaval."

The team's findings mark just the beginning of a broader investigation. Courtney-Davies and his colleagues hope to inspire further exploration across North America. "If such features formed in Colorado during Snowball Earth, they probably formed in other spots around North America, too," he said.

This research could help geologists build a more comprehensive picture of Earth’s ancient climate and the forces that shaped its evolution.

As scientists continue to piece together this icy puzzle, the Tava sandstones of Colorado stand as a testament to the planet's ability to endure—and transform—through its most extreme phases.

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