Even the balmy tropics may once have been crushed by colossal masses of ice.

A severe ice age dominated Earth720 to 635 million years ago, much earlier dinosaurs traveled the earth. But it is not certain that the entire world froze during the glaciations of this extreme and long-lasting episode, nicknamed “Snowball Earth”. Now, new evidence from Colorado, a region once located in the tropics, suggests powerful glacier widespread even in the hottest regions of the Earth.

“This study presents the first physical evidence that Snowball Earth reached the cores of the continents at the equator,” Liam Courtney-Davies, a geologist at CU Boulder who led the new research, said in a statement. The research was recently published in Proceedings of the National Academy of Sciencesa leading scientific journal.

A dramatic reduction in greenhouse gases that trap heat on the planet — especially carbon dioxide – may have triggered the slide to a frozen orb. Previous research suggested that even though the Earth’s average temperature fell well below freezing, some of the ocean and land surface resisted becoming transformed or covered in thick, hard ice.

But evidence seen in the high mountains of Colorado indicates the presence of thick ice in the tropics.

The telltale rocks are called Tava Sandstone and are exposed in the Rocky Mountains. As you may have guessed, sandstone starts out as sand on the surface, but it is compacted by different activities, such as river grains being buried under layers and layers of silt. In this case, researchers say the Tava sandstone resembles the type of features found under ice sheets, like those today. Antarctic.

To see if heavy glaciers may have compacted this once-tropical sandstone (shown below), the researchers dated the mineral veins that ran through the sandstone. They shot these ancient rusty minerals with a laser, which released uranium, a radioactive element common in the Earth’s crust. Importantly, uranium naturally decays at a constant rate, which provides a dating technique and a good idea of ​​when something formed.

Orange Tava sandstone exposed at the top of the Rocky Mountains.
Credit: Christine Siddoway / CU Boulder

The dark reddish-brown bands are the layers of Tava sandstone that researchers believe were crushed under heavy glaciers during Snowball Earth.
Credit: Liam Courtney-Davies / CU Boulder

The result? The dating of the uranium corresponds to the Snowball Earth period, hundreds of millions of years ago.

This is a compelling discovery, suggesting that large glaciers compressed a once-tropical Colorado. But this is only one area studied. Further studies are needed to truly understand the extent of this vast ice cover on Earth.

“We want to get the word out so that others will try to find these features and help us build a more complete picture of Snowball Earth,” Courtney-Davies said.

Eventually the extreme ice age ended, perhaps fueled by a asteroid strike which blew a plethora of heat-trapping gases in the atmospheremelting the ice and forcing the heavier glaciers to retreat. The Earth’s crust continues to reveal our planet’s wild journey over billions of years – a journey that continues today The ever-moving surface of the Earth.