Geologists have recently discovered compelling evidence from Colorado that suggests Earth may have been encased in ice all the way to the equator hundreds of millions of years ago. This finding supports the “Snowball Earth” hypothesis, which suggests that the planet was once nearly or entirely frozen over. This phenomenon is thought to have occurred between 720 and 635 million years ago, during a period marked by an extreme and possibly self-reinforcing drop in global temperatures. During this time, ice sheets several miles thick are believed to have covered most, if not all, of Earth’s surface.
A research team led by the University of Colorado Boulder has now provided some of the first physical proof that Snowball Earth conditions reached deep into the interiors of continents at equatorial latitudes. Their study, which will be published in the Proceedings of the National Academy of Sciences, was conducted by a group of scientists from multiple institutions, including Colorado College, the University of California at Santa Barbara, and the University of California at Berkeley. The research focuses on a unique geological formation in Colorado’s Rocky Mountains called the Tava sandstones, which could hold crucial clues about this frigid chapter in Earth’s past.
Using advanced dating techniques like laser ablation mass spectrometry, the researchers analyzed mineral samples from the Tava sandstones, which are located along Colorado’s Front Range. This method involves striking minerals with lasers to release specific atoms, which helps determine the age of the rocks. The scientists discovered that the Tava sandstones were likely buried beneath massive ice sheets between 690 and 660 million years ago, as the sheer weight of these glaciers pushed them underground. According to lead author Liam Courtney-Davies, this discovery sheds light on a vital period in Earth’s geological and biological history, as it was during this era that the first multicellular organisms may have emerged following the eventual thawing of Snowball Earth.
The Snowball Earth theory was first proposed in 1992 by geologist Joseph Kirschvink. While scientists generally agree that global temperatures reached unprecedented lows, there has been ongoing debate about whether ice truly covered every inch of the planet. Although thick ice deposits from this period have been found along ancient coastlines, similar formations in the interiors of continents near the equator had remained elusive. This gap in evidence is what made the Colorado findings so significant. During the Snowball Earth period, what is now Colorado would have been positioned over the equator as part of the supercontinent Laurentia. Therefore, evidence of glaciers in Colorado could imply that these massive ice sheets spanned much of Earth’s surface, including equatorial regions.
To understand the forces that shaped the Tava sandstones, Courtney-Davies and his team examined the structures of these rocks. At first glance, they might seem like simple yellow-brown rock formations that run in narrow, vertical bands, yet to geologists, these formations reveal signs of having been buried and reshaped under extreme pressures. The rocks contain a pattern of mineral veins that indicate they were once buried deep underground, likely due to the pressure exerted by vast ice sheets. Such formations, known as “injectites,” are often associated with glacial ice, particularly in places like Antarctica today.
By calculating the ages of the minerals within the Tava sandstones, the team was able to reconstruct their history. When they hit the mineral veins, rich in iron oxide, with a laser, small amounts of radioactive uranium were released. Since uranium decays into lead at a predictable rate, it can act as a natural “clock,” allowing researchers to date geological formations. The team’s findings suggested that the Tava sandstone was pushed below the Earth’s surface during Snowball Earth. This was likely due to the immense weight of thick ice sheets in what is now Colorado, forcing the sand down into bedrock.
For the researchers, these findings offer a rare glimpse into Snowball Earth and provide clues about how life on Earth might have responded to such extreme climate conditions. Co-author Rebecca Flowers expressed excitement at the opportunity to study what are currently the only confirmed Snowball Earth deposits in Colorado. She and her team hope that these insights can deepen our understanding of Earth’s climate evolution and the environmental pressures that may have influenced the development of early life.
The researchers plan to continue their work, as similar features could exist elsewhere in North America, potentially allowing for a more complete reconstruction of Snowball Earth. Courtney-Davies hopes that geologists in other regions will join the search for these unique formations, helping to build a more comprehensive picture of the ancient frozen world.