Glaciers, like the one seen here, may have once carved through the Earth's crust similar to how they can carve valleys in rock today. (PositiveTravelArt/Shutterstock)
In a nutshell
- Ancient “snowball Earth” glaciations acted as giant geological bulldozers, scraping deep into Earth’s crust and releasing uranium and other elements into the oceans.
- Researchers found evidence of this process by analyzing zircon mineral grains in ancient rocks from Scotland and Ireland, showing more diverse zircon ages during glacial periods.
- These glacial erosion patterns may have altered ocean chemistry in ways that helped set the stage for the later explosion of complex life forms.
PERTH, Australia — Long before humans walked the Earth, ice reshaped our planet in dramatic ways. During the Neoproterozoic era (717–580 million years ago), a series of extreme glaciations transformed Earth’s geology and chemistry. These “snowball Earth” events weren’t just climate anomalies; they profoundly altered the landscape and may have set the stage for the later explosion of complex life.
A Curtin University research team uncovered evidence that these massive glaciers acted like giant geological bulldozers. The findings, published in Geology, revealed that as they scraped deep into Earth’s ancient continental crust, they sent a flood of weathered materials into the oceans, altering ocean chemistry and influencing the evolution of early complex life.
“When these giant ice sheets melted, they triggered enormous floods that flushed minerals and their chemicals, including uranium, into the oceans,” says lead study author Chris Kirkland from Curtin University, in a statement. “This influx of elements changed ocean chemistry at a time when more complex life was starting to evolve.”
How did this happen?
To understand what was happening during these ancient glaciations, we need to rewind to about 800 million years ago. Back then, Earth looked completely different. Most landmasses were clumped together in a supercontinent called Rodinia that straddled the equator. As this massive continent started breaking apart, it triggered a series of catastrophic climate changes that plunged the planet into some of the most extreme ice ages in its history.
Chris Kirkland)
Scientists have debated for years about what caused these snowball Earth events. The leading theory suggests that as Rodinia fragmented, massive volcanic eruptions spewed vast quantities of basalt across the land. When this newly exposed rock weathered in the tropical climate, it pulled carbon dioxide out of the atmosphere, cooling the planet. This cooling effect was reinforced when phosphorus from these rocks washed into the oceans, fueling algal blooms that sucked up even more CO2.
But instead of focusing on what triggered these glaciations, Kirkland’s team wanted to understand their consequences, particularly how sediments moved around during and after these global deep freezes.
Clues from the past
So how do you study something that happened hundreds of millions of years ago? The researchers examined ancient sandstones from the Dalradian Supergroup, geological formations that stretch across parts of Scotland and Ireland. These rocks preserve a detailed record of sedimentation during the Neoproterozoic, including distinct layers deposited during three major glacial episodes: the Sturtian (717-658 million years ago), the Marinoan (645-635 million years ago), and the Gaskiers (580 million years ago).
The key to unlocking this ancient history was tiny mineral grains called zircons found within these sandstones. These durable crystals contain uranium that decays at a predictable rate, allowing scientists to determine precisely when each grain originally formed. By analyzing hundreds of zircon grains from rocks deposited before, during, and after glacial periods, the team could trace how sediment sources changed over time.
They found that the diversity of zircon ages spiked dramatically in sediments associated with glacial periods. This meant that ice sheets were carving into deeper, older rocks that hadn’t been eroded much before. The pattern repeated at each glacial interval, showing a consistent relationship between global freeze events and more intensive erosion of continental interiors.
Powerful agents of erosion
This finding overturns the idea that snowball Earth’s ice sheets were static features. Instead, they were dynamic, erosive forces that actively carved into Earth’s ancient crust. The researchers suggest these were wet-based glaciers with liquid water at their base, making them especially effective at eroding the underlying rock, like sandpaper with water constantly lubricating the surface.
The researchers also noticed something interesting happening right after each glacial period. The diversity of zircon ages would slightly decrease, a phenomenon they called “back-steps.” They interpret this as evidence of rivers reworking the glacially eroded material during warming periods. As ice sheets retreated, rivers would have sorted through this debris, washing away softer materials while leaving behind harder, more resistant minerals.
This two-phase process—first glacial grinding, then river sorting—had profound implications for how elements moved through Earth’s systems. The researchers found that after glaciation, there was a decrease in the ratio of apatite to zircon, along with increases in monazite-to-zircon and rutile-to-zircon ratios. This pattern suggests glaciers were not only eroding the land but also shifting the composition of sediments that ended up in the ocean.
Did glacial erosion help trigger the Cambrian explosion?
The sorting process had major implications for Earth’s chemistry. As glaciers ground down ancient continental rocks, they released significant amounts of uranium and other elements into the oceans. Previous studies have shown increases in oceanic uranium after Neoproterozoic glaciations, but scientists usually attributed these changes to shifts in ocean oxygenation. This new study suggests that enhanced metal delivery from intensified erosion also played a crucial role.
The Neoproterozoic era immediately preceded the Cambrian explosion, that remarkable period when complex multicellular life suddenly diversified into the ancestors of most major animal groups alive today. The changes in ocean chemistry driven by these glacial erosion patterns might have helped create conditions favorable for this evolutionary burst.
As a bonus discovery, the researchers found evidence of relatively young zircons (904-941 million years old) throughout the Irish sections of the Dalradian Supergroup. These were likely eroded from mountains in what is now Norway and Sweden, providing valuable information about the geography of the time.
What this means for today’s climate change
“This research is a stark reminder that while Earth itself will endure, the conditions that make it habitable can change dramatically,” says Kirkland. “These ancient climate shifts demonstrate that environmental changes, whether natural or human-driven, have profound and lasting impacts. Understanding these past events can help us better predict how today’s climate changes might reshape our world.”
The findings show how Earth’s most extreme ice ages didn’t just remodel the landscape but altered the fundamental cycling of elements through the planet’s systems. By acting as a geological bulldozer, Neoproterozoic glaciations swept away ancient crustal material, redistributed it into ocean basins, and drove changes in ocean chemistry that may have influenced the evolution of complex life. Climate shifts, whether in the distant past or the present, can transform Earth in profound and lasting ways.
Paper Summary
Methodology
The researchers analyzed zircon grains from sandstone samples collected across Scotland and Ireland using laser ablation mass spectrometry to determine their ages. Statistical analysis helped identify patterns in the diversity and distribution of zircon ages throughout the rock layers, particularly focusing on changes before, during, and after glacial periods.
Results
Key findings include: 1) Sharp increases in zircon age diversity during glacial periods, indicating ice sheets were eroding deeper, older rocks; 2) Higher proportions of ancient zircons (>2 billion years old) in glacial deposits; 3) Slight decreases in zircon diversity after glacial periods but never returning to pre-glacial levels; 4) Increased average density of zircon crystals in post-glacial sediments, suggesting preferential weathering of less durable grains.
Limitations
Limitations include relatively sparse sampling across the regions studied, possible recycling of zircons from older sedimentary rocks, and potential biases from selective mineral preservation during transport and metamorphism. The connections between erosion patterns and broader geochemical changes remain somewhat speculative without more direct geochemical measurements.
Discussion and Takeaways
The research shows Neoproterozoic glaciations dramatically altered Earth’s sedimentary dynamics, with wet-based glaciers actively eroding continental interiors. The two-stage process of glacial grinding followed by fluvial sorting would have significantly affected elemental cycling, contributing to changes in ocean chemistry that may have influenced the evolution of complex life. The findings demonstrate how climate events can trigger chain reactions through Earth’s interconnected geological, chemical, and biological systems.
Funding and Disclosures
The paper doesn’t explicitly state its funding sources, but the research involved collaboration between scientists from three countries: Curtin University in Western Australia, the University of Portsmouth in the UK, and St. Francis Xavier University in Nova Scotia, Canada. The research was conducted through Curtin’s Frontier Institute for Geoscience Solutions, specifically within the Timescales of Mineral Systems Group. The authors thanked several individuals who helped with the study, including B. McDonald, T. Prave, W. Guenthner, M. Krabbendam, E. Rugen, and U. Schaltegger, though their specific contributions weren’t detailed.
Publication Information
“The Neoproterozoic glacial broom” was authored by C.L. Kirkland, R.A. Strachan, D.B. Archibald, and J.B. Murphy, published in Geology in 2025. The research was a collaboration between Curtin University (Australia), the University of Portsmouth (UK), and St. Francis Xavier University (Canada).
