Researchers find strong evidence for “Snowball Earth” theory

Snow in northeastern United States.

A new study published in the Proceedings of the National Academy of Sciences presents strong evidence that massive glaciers covered the entire globe during the Cryogenian Period, including thick ice sheets that likely formed over Colorado. Led by the University of Colorado Boulder, the research focuses on the Front Range of Colorado's Rocky Mountains, where geologists found physical evidence related to the Snowball Earth hypothesis. The study describes a missing link found in an unusual pebbly sandstone encapsulated within the granite that forms Colorado's Pikes Peak.

Liam Courtney-Davies, the lead author of the study and a postdoctoral researcher in the Department of Geological Sciences at CU Boulder, stated, "This study presents the first physical evidence that Snowball Earth reached the heart of continents at the equator." The discovery that glaciers reached the center of continents, where conditions would have been very dry, deepens the mystery of where and how life survives. Physical evidence that ice sheets covered the interior of continents in warm equatorial regions had eluded scientists until now.

During the Snowball Earth period, around 720 to 635 million years ago, the Earth cooled so much that massive ice sheets encased the entire planet like a giant snowball. Temperatures plummeted, and ice sheets that may have been several miles thick crept over every inch of Earth's surface. Evidence of ice in Colorado dating back 661 million years supports this hypothesis. Scientists believe that ice sheets possibly surrounded the entire planet, even at the equator, where it is warmer today.

Despite decades of research, scientists have not agreed whether the entire globe actually froze during the Snowball Earth period. Initially, geologists were skeptical about finding far more ancient hints of glaciers in tropical regions. It seemed implausible that the planet had ever been cold enough for thick sheets of ice to have reached the equator. The new findings further cement the global Snowball Earth hypothesis, which suggests that this global deep freeze endured for tens of millions of years.

The study focuses on the Tava sandstones, a series of rocks nicknamed the Tavakaiv or "Tava," which hold clues to the frigid period in Earth's past. The Tava rocks are composed of solidified sand injectites, formed when sand-rich fluid was forced into underlying rock, similar to fracking for natural gas or oil. To the untrained eye, the Tava sandstones might seem like ordinary yellow-brown rocks running in vertical bands less than an inch to many feet wide. For geologists, however, they have an unusual history; they likely began as sands at the surface of Colorado at some point in the past.

The researchers used a dating technique called laser ablation mass spectrometry, which zaps minerals with lasers to release some of the atoms inside. Recent advancements in laser-based radiometric dating allowed the researchers to measure the ratio of uranium to lead isotopes in iron oxide minerals, revealing how long ago the individual crystals formed. This allowed them to figure out an age bracket for the sand injectites, which must have formed between 690 million and 660 million years ago, during the Cryogenian Period.

The group suspects that thick ice sheets formed over Colorado during the Snowball Earth period, exposing the sands to intense pressures. The researchers envision the following scenario for how the sand injection happened: A giant ice sheet with areas of geothermal heating at its base produced meltwater, which mixed with quartz-rich sediment below. Similar to fracking for natural gas or oil today, the pressure cracked the rocks and pushed the sandy meltwater in, eventually creating the injectites seen today.

Liam Courtney-Davies says, "These are classic geological features called injectites that often form below some ice sheets, including in modern-day Antarctica." He added, "You have the climate evolving, and you have life evolving with it. All of these things happened during Snowball Earth upheaval." The researchers argue that mineral veins injected into sandstones are a sure sign of a combination of glacial pressure and geothermal heating.

At the time of the Snowball Earth period, Colorado rested over the equator as a landlocked part of the ancient supercontinent Laurentia, and the Tava rocks found on Pikes Peak would have formed close to the equator. If glaciers formed in Colorado, scientists believe they could have formed anywhere on Earth. The Colorado sites fit the criteria of being tropical, low altitude, and far from continental margins at the relevant time.

Rebecca Flowers, co-author of the study and professor of geological sciences at CU Boulder, said, "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." The discovery provides crucial evidence supporting the idea that the entire planet may have been encased in ice.

The findings also have implications for understanding the history of life on Earth. Before the Cryogenian period, life on Earth was dominated by single-celled organisms. After Snowball Earth thawed, the earliest examples of large organisms appeared during the Ediacaran period, which lasted from 635 to 541 million years ago. Scientists still don't understand the processes which led to this explosion in life after Snowball Earth.

Liam Courtney-Davies emphasized the importance of the study, saying, "We have to better characterize this entire time period to understand how we and the planet evolved together." He added, "If such features formed in Colorado during Snowball Earth, they probably formed in other spots around North America, too." The researchers hope that the secrets of these elusive Cryogenian rocks in Colorado will lead to the discovery of further terrestrial records of Snowball Earth.

Such findings can help develop a clearer picture of Earth during climate extremes and the processes that led to the habitable planet we live on today. The researchers' results support that a Great Unconformity near Pikes Peak must have been formed prior to Cryogenian Snowball Earth. This finding is at odds with hypotheses that attribute the formation of the Great Unconformity to large-scale erosion by Snowball Earth ice sheets themselves.

Ultimately, the study not only sheds light on a critical phase in Earth's geologic history but also deepens the mystery of where and how life survives during extreme climate events. The researchers' work underscores the interconnectedness of Earth's climate and the evolution of life, providing new avenues for exploration and understanding.

Sources: Science Alert, Cosmos, Phys.org, IFLScience, Science Daily

This article was written in collaboration with generative AI company Alchemiq