August 16, 2022

The crater under the Greenland ice sheet is 58 million years older than previously thought

The crater under the Greenland ice sheet is 58 million years older than previously thought

Bed topography under Hiawatha Glacier in Northwest Greenland (Kjær et al., 2018)

In 2018, researchers discovered a massive device, 19 mile span It is hidden under the Greenland ice sheet. A March 2022 study used the argon age of sand grains to determine that the meteorite impact occurred nearly 58 million years ago. The study, written by Gavin G. Kenny of the Swedish Museum of Natural History and his team, details the initial discovery of the crater and the methods used to determine the time of the impact.

This effect is distinct from others of its kind: it was discovered by only one Ice penetrating radar It is used to better understand the surface beneath Greenland’s Hiawatha Glacier. This was in 2018. Before Kenny and his colleagues could begin collecting data, they had to travel long distances to reach the frozen, remote impact site. This research was very expensive and the team spent many hours collecting grains of sand and glacier melt water from the impact site.

The researchers then measured the ratio of the two argon isotopes Ar-40 and Ar-39 in the sand grains—a laborious process because Ar-40 makes up about 99.5 percent of all argon in the Earth. Establishing the argon ratio allowed the researchers to determine the age of the surrounding sand grains using an equation. When Ar-40 is exposed to radiation, it breaks down into Ar-39. The residual concentration of Ar-40 is measured, and a higher concentration of Ar-40 indicates older age. All the seeds tested were more than 50 million years old. This placed the impact precisely in the geological period called the Paleocene.

The scientific community previously believed that the impact occurred in the late Pleistocene, 1 million years ago, when the Greenland Ice Sheet was present. However, new dating evidence from this study suggests that the impact occurred during the Paleocene. The Paleocene (56-66 million years ago) is known as a period of mountain building in which the land was small herbivorous mammals and apparently devoid of dinosaurs. At that time, Greenland was covered by a temperate forest instead of the thick layer of ice that now covers the entire impact zone.

The discovery of this crater, only four years ago, was the product of a hump. When Danish geologist Nikolaj Larsen studied detailed maps of Greenland, he noticed a circular structure under the glacier, which prompted further research. He then selected a team of researchers and they set off on a journey to Greenland. The crater they found was the first to be discovered beneath a continental ice sheet. In general, craters on the ground disappear quickly, and for those that persist, it is often difficult to determine their exact age. Therefore, the accuracy of using argon under the Hiawatha glacier is remarkable.

A previous study, published in 2018 by Elizabeth Silber, explored the possible timing of the Hiawatha collision before argon dates were available. His primary research goal was to determine whether the impact occurred before or during the Pleistocene, or last ice age, which occurred 2,580,000 to 11,700 years ago. The work of Silber, a geologist at the University of Western London, Ontario, paved the way for research in the following years.

Speaking to GlacierHub via email, Silber discussed the challenges he faced during his research. He said “[the] Hiawatha’s strike structure is somewhat muted compared to what we’d expect from an aerial strike. His comments indicate that the crater is shallow and has disturbed the peak rings. Peak ring openings They have rings that surround the center of the opening. Consequently, it is not easy to determine whether the crater structure is due to “preferential and slow erosion rates (if the impact crater formed when there was no ice sheet in the area), or because a thick ice sheet absorbed some has done. from the energy of the blow.” Both possibilities cause the crater to have “less distinct morphological features”. The models used by Sieber showed both scenarios (pre-Pleistocene or Pleistocene) equally plausible, so the newly published study using argon dating was “exciting because this age estimate is in agreement with our modeling results for the structure. An older hit points, it matches.” Seeber said.

This begs the question: If the impact occurred much earlier than previously thought, how would this change in timing change its perceived impact on global climate? Because the initial age estimate placed the impact in the Pleistocene, it was previously thought that the impact may have been associated with the beginning of the era. The cold period of the Young Sea About 11,000 years ago the Younger Dryas was a period of extreme cooling that temporarily reversed global warming. It is unknown what caused this event, but placing the Hiawatha collision at 58 million years ago rules out any correlation between the two.

However, this impact occurred long before the Pleistocene and is no longer likely to have affected human life. More research is necessary to precisely identify specific effects, but given the size of the crater, it is likely to have had a significant impact on global climate. Many agree that the meteorite’s size alone could have thrown large amounts of water vapor and debris into the atmosphere after the impact, triggering a period of global cooling. Furthermore, the timing of the impact occurred within the time frame of the Paleocene carbon isotope maximum, when there was a peak in the presence of carbon-13 in the atmosphere. High levels of carbon-13 in the atmosphere are further evidence of a large meteorite impact that disrupts the normal levels of carbon-13.

As Liam Colgan told GlacierHub, understanding the behavior of ice in earlier time periods is important to better understand their current effects. Colgan is a climatologist and editor for Ice magazine Focusing on glaciers as indicators of climate change. He was not affiliated with the recent study. “What happened in the past is still affecting the ice sheet today,” he said. Ice properties of the last ice age (or Pleistocene) are different from those of today’s Holocene ice.

According to Colgan, understanding the transition depths of ice from the last Ice Age to more recent Holocene ice is essential to predicting ice behavior, a critical question for predicting future water level rise. Although recent research has placed the impact in the Paleocene, the resulting difference in topography likely influenced the ice movement seen today.

The use of glacial meltwater to obtain sand samples, as well as the use of argon dating, has been a major success in research in remote and difficult terrain. These tactics can be used to analyze current craters, allowing us to better understand our Earth’s history and how to better predict the effects of future events.


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