Ancient glaciers paved way for life on Earth

The movement of massive glaciers during global ice ages contributed to the rise of complex life, new research reveals.

By analysing zircon crystals in ancient rocks, geologists found that as glaciers flowed across the Earth’s surface, they carved deep into the crust and released key minerals from below.

These minerals were later flushed out to sea, where they altered ocean chemistry and helped create the conditions for complex life.

“We expected to find evidence of glaciers scouring the land, but what we found was even more striking – glaciers weren’t just scraping away rock, they were fundamentally altering the planet’s geochemical cycles in ways that may have helped trigger life-altering changes,” says Chris Kirkland, from Curtin University’s Frontier Institute for Geoscience Solutions.

“This study highlights how Earth’s land, oceans, atmosphere and climate are intimately connected.”

Snowball Earth

The study, published in the journal Geology, focuses on Neoproterozoic Snowball Earth events: a series of global ice ages around 700 to 600 million years ago, when the planet was almost entirely covered in ice.

These frigid periods are thought to be a critical moment in the history of life, setting the stage for the biological revolution that followed. For billions of years single-celled organisms had dominated the Earth. But molecular and fossil evidence shows after Snowball Earth thawed, the first multicellular life evolved. The earliest examples of large animals are seen during the Ediacaran period (635–541 million years ago).

“Australia holds some of the most critical evidence for both the Snowball Earth glaciations and the rise of complex life in the aftermath,” Kirkland notes.

“Perhaps the most important link between Snowball Earth and the evolution of life can be found in Australia’s Ediacara Hills in South Australia. These fossil-rich deposits, dating to around 575–541 million years ago, provide the earliest known record of large, complex, soft-bodied life, which the snowball set the geochemical scene for.”

But how exactly did these deep freezes affect the planet’s geology and chemistry?

Scientist have long been trying to answer this question. For example, some previous research has suggested that the glaciers were capable of grinding down mountains and dumping mineral nutrients like phosphorous into the oceans, where algae feasted on it.

This new study adds another piece to the puzzle.

“Our findings provide new evidence that Snowball Earth was not just a period of deep freeze but a time of intense geological and geochemical change,” Kirkland says. “Glaciers actively shaped the land and influenced global geochemical cycles.”

Snowball Earth’s massive glaciers weren’t passive. They were capable of cutting deep into the Earth’s crust as they moved, grinding rocks into fine sediment and releasing the minerals within. These minerals were rich in elements like uranium.

Then, when Snowball Earth began to thaw and the giant ice sheets melted, the floods flushed the minerals out to sea.

“This process increased the delivery of metals into the ocean, changing its chemistry in a way that may have contributed to shifting geochemical cycles at a time when more complex life was getting started,” Kirkland says.

“For example, uranium levels in the ocean are typically linked to oxygen availability – higher uranium levels suggest a more oxygen-rich environment.”

As melting accelerated, the delivery of nutrients may have helped to set off a chain reaction that made the ocean more hospitable to complex life.

“This could have paved the way for the explosion of multicellular organisms that followed in the Ediacaran period, ultimately leading to the rise of animals,” Kirkland says.

Tiny time capsules

But how can geologists know how sediments moved hundreds of millions of years ago?

In collaboration with researchers from the University of Portsmouth, UK, and St. Francis Xavier University, Canada, Kirkland looked at zircons in sandstone deposits from during and after Snowball Earth events, found in present-day Scotland and Ireland.

“Zircons are tiny, tough minerals that act like time capsules of Earth’s history,” Kirkland explains. “Because zircons are so durable, they survive for billions of years and can be transported by rivers, glaciers, and wind into sedimentary layers.”

For example, a few grains of zircon found in rocks in Western Australia’s Jack Hills have been dated to nearly 4.4 billion years ago.

This dating is possible because zircon contains small amounts of uranium, which radioactively decays into lead at a known rate. If scientists can then determine the ratio of uranium and lead present in the rock, they can calculate the age of a sample.

“This provides a ‘DNA fingerprint’ of where material was being scraped up from,” Kirkland says. “If glaciers were eroding older bedrock, we would see an influx of older zircons in the sediment. By analysing how the variety of zircon ages changed through different rock layers, we could reconstruct how glaciers reshaped the landscape and influenced the chemistry of the oceans.”

The results further suggest that the glaciers continued to influence the planet even after Snowball Earth melted.

“One of the key discoveries [of this paper] was that after the ice sheets melted, rivers and other processes further sorted and transported the glacial debris, reshaping landscapes even after the glaciers were gone,” Kirkland says.

Ancient climate, modern warnings

Looking into the deep past can provide us with context for our future.

“This research is a stark reminder that while Earth itself will endure, the conditions that make it habitable can change dramatically,” Kirkland notes.

“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.”