A collection of rocks found in Colorado’s Rocky Mountains may provide insights into a chilling epoch in Earth’s history, when glaciers several miles thick enveloped the entire planet.
Researchers have found compelling evidence in Colorado suggesting that massive glaciers once extended all the way to the equator, turning the Earth into a massive ice-covered sphere.
The investigation, spearheaded by the University of Colorado Boulder, supports a longstanding theory called Snowball Earth. This theory proposes that from approximately 720 to 635 million years ago, unknown factors triggered a dramatic shift in the planet’s climate. Global temperatures dropped significantly, leading to the formation of ice sheets that could have been several miles thick, covering every part of the Earth’s surface.
“This study provides the first tangible evidence that Snowball Earth reached continental equators,” stated Liam Courtney-Davies, the study’s lead author and a postdoctoral researcher in CU Boulder’s Department of Geological Sciences.
The findings will be published in the Proceedings of the National Academy of Sciences. Co-authors include Rebecca Flowers, a geological sciences professor at CU Boulder, along with researchers from Colorado College, UC Santa Barbara, and UC Berkeley.
The research focuses specifically on the Front Range of Colorado’s Rocky Mountains, where a group of rocks called Tavakaiv, or “Tava,” sandstones offers clues about this icy chapter in Earth’s history, according to Courtney-Davies.
The team employed a dating method called laser ablation mass spectrometry, which uses lasers to fragment minerals and release internal atoms. This technique demonstrated that these rocks had been buried underground between roughly 690 to 660 million years ago, likely due to the immense weight of glaciers above them.
Courtney-Davies remarked that the study could enhance scientists’ understanding of not only geological changes but also the history of life on Earth. It is believed that the first multicellular organisms might have emerged in oceans shortly after the Snowball Earth thawed.
“As the climate evolved, so did life. All these transformations happened during the tumultuous period of Snowball Earth,” he explained. “To grasp how we and our planet have developed together, we need to thoroughly investigate this entire era.”
Looking for ice
The term “Snowball Earth” was first introduced in a 1992 paper by American geologist Joseph Kirschvink.
Despite extensive research over the years, scientists have yet to reach a consensus on whether the entire planet actually froze over. For instance, geologists have found evidence of thick ice along ancient shorelines, but not within continental interiors near the equator.
This is where Colorado comes into play. During that time, the area was not positioned at its current northern latitude, but instead lay over the equator as part of the ancient supercontinent Laurentia.
If glaciers formed in this location, it suggests they could have formed anywhere else as well.
Diving deeper
The pursuit for this elusive evidence led Courtney-Davies and his team to the Tava sandstones. Today, these geological features can be observed at various locations along Colorado’s Front Range, especially around Pikes Peak. To an untrained observer, they might appear as ordinary yellow-brown rocks arranged in vertical bands, measuring from less than an inch to several feet wide.
However, for geologists, these formations have a fascinating backstory. These rocks likely originated from surface sands in Colorado, but later geological forces pushed them underground—similar to claws gripping the Earth’s crust.
“These are classic geological structures known as injectites, often formed beneath ice sheets, including those seen in modern Antarctica,” Courtney-Davies explained.
He aimed to determine whether the Tava sandstones were also associated with ice sheets. To achieve this, the researchers analyzed the ages of mineral veins that cut through these formations. By taking small samples rich in iron oxide (essentially rust) and using lasers, they released tiny amounts of radioactive uranium present in the minerals. Since uranium decays into lead at a consistent rate, the researchers employed this as a natural chronometer to gauge the age of the rocks.
It was a significant discovery: The results indicate that the Tava sandstone had been buried beneath the surface during the period of Snowball Earth. The team suspects that thick ice sheets developed over Colorado, exposing the sands to intense pressure, ultimately forcing them down into the underlying bedrock.
“We’re thrilled to have had the chance to uncover the history of the only identified Snowball Earth deposits in Colorado,” Flowers said.
The researchers are just getting started: If similar features emerged in Colorado during Snowball Earth, it’s likely they appeared in other regions of North America as well, Courtney-Davies stated:
“We aim to encourage others to search for these formations to help us create a more comprehensive understanding of Snowball Earth.”