Scientists Uncover Evidence That the Late Cretaceous Hosted Icy Conditions in Antarctica

Icy Conditions in Antarctica During the Late Cretaceous, According to New Evidence Discovered by Scientists

Browse LatestLY for the most recent Science articles and stories. Pretend it’s the end of the Cretaceous period, between 66 and 100 million years ago. Dinosaurs and strange early birds populate the land, yet the familiar shark may be found in the vast waters that make up 82% of the planet’s surface. Redwood trees and other conifers are emerging, along with roses and other flowering plants and the insects that necessitate their pollination, such as bees, termites, and ants. First and foremost, there is not a single ice cap in sight, and the entire world is consistently hot, vulnerably humid, and riddled with volcanoes.

Let’s imagine it’s the Cretaceous Period (about 66-100 Ma) and we’re in Washington, DC. The land is populated by dinosaurs and strange early bird species, while the shark as we know it swims in the primordial oceans that encompass 82% of Earth’s surface. Bees, termites, and ants have emerged along with the redwoods and other conifers, roses, and other flowering plants. Most notably, there is not a single ice cap in sight, and the entire region is perpetually hot, volcanically active, and muggy.

A team of researchers from UC Santa Barbara, the University of Oregon, and the University of Manitoba, however, has found evidence that freezing conditions actually persisted near the South Pole.

As UCSB geologist John Cottle put it, “it wasn’t just a single-valley glacier; it was probably multiple glaciers or a large ice sheet.” This runs counter to the common perception that the Late Cretaceous was “hot everywhere,” but there is evidence that polar ice existed even at the height of global greenhouse conditions.

The geologists have released their findings in a new report that appears in Nature Communications.

Scientists Uncover Evidence That the Late Cretaceous Hosted Icy Conditions in Antarctica

A Prehistoric Puzzle

Okay, let’s jump to the present day. Let’s imagine we’re in Antarctica. The Butcher Ridge Igneous Complex is a massive outcrop of igneous rock along the Transantarctic Mountains, close to the Ross Ice Shelf, and it is cold and desolate here (BRIC).

I first heard about these rocks when I was a graduate student around 20 years ago, and they’re really odd,” Cottle remarked. Large levels of glass and layered alteration, among other things, are uncommon in surrounding rock formations and imply substantial physical, chemical, or environmental activities that modified their mineral composition, making the BRIC remote even by today’s Antarctic exploration standards.

On a recent mission, Cottle was able to take samples from the BRIC for the first time, and as he and his team were analyzing its formation, they came upon an “unusually big volume of water.”

His explanation was something along the lines of, “So you have a highly hot rock that interacts with water, and as it cools, incorporates it into the glass.” In terms of origin, “if you look at the composition, then you can tell something about where that water originated from. It can exist as hydroxyl, which tells you that it presumably came from the magma, or it could be molecular, which tells you that it is probably external.”

They hypothesized that water present in the magma would cause the rock to change as it cooled. However, what they actually uncovered was evidence of a climatic mechanism that was previously assumed to have been nonexistent at the time.

Spectroscopic study of the samples revealed that while some of the water did start with magma as it rose from the Earth’s deep, groundwater was also integrated into the glass as the molten rock cooled just beneath the surface.

The majority of the water in these rocks is not naturally occurring, we determined,” Cottle added. We then determined that the water’s isotopic ratios of oxygen and hydrogen were consistent with those found in Antarctic snow and ice. Cottle and his team also used argon-argon geochronology to date the rock and its modification, providing additional confidence in their result.

Scientists Uncover Evidence That the Late Cretaceous Hosted Icy Conditions in Antarctica

These rocks are Jurassic in age, which is roughly 183 million years old,” he explained. What they didn’t know, despite recovering the rock’s original age (Jurassic), was when the change occurred (Cretaceous). As he elaborated, “so as these rocks cooled and were altered, it also reset the argon isotope as well, and you can correlate the date of the alteration to the composition of the alteration.”

Other, similar volcanic rocks with a Cretaceous alteration age can be found around 700 km north of the BRIC, suggesting that polar ice may have been regionally pervasive in Antarctica at that time. To better gauge the magnitude of the glacier, he continued, “we’d like to go to other areas in Antarctica and see if we can recover the same results that we’ve previously obtained.”

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If large ice sheets were discovered that dated back to the Cretaceous, Cottle said, “we would have to think about the Cretaceous and Antarctica quite differently than we do now.” This might not change our overall picture of a hot and humid Earth at that time, but it would force us to rethink the period. Demian A. Nelson (corresponding author) and Ilya N. Bindeman (University of Oregon) and Alfredo Camacho (University of Manitoba) also contributed to the research presented here. (ANI)

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