Crater under Greenland glacier 58 million years earlier than previously thought
Bed topography under the Hiawatha Glacier in northwestern Greenland (Kjær et al., 2018)
In 2018, researchers discovered a huge, 19-mile-wide crater Hidden under the Greenland Ice Sheet.One March 2022 Research The meteorite impact was determined to have occurred nearly 58 million years ago (Ma) using argon dating of sand grains. The study, authored by Gavin G. Kenny and his team at the Swedish Museum of Natural History, details the initial findings of the crater and the method used to time the impact.
This effect is different from other effects of its kind: it is only caused by a ice detection radar Used to better understand the surface beneath the Warsaw Glacier in the Greenland Sea. That was in 2018. Before Kenny and his colleagues began collecting data, they had to travel long distances to reach the remote location where the impact freezes. The study was expensive, and the team spent a lot of time collecting sand grains from the impact site that were carried by streams fed by glacial meltwater.
The researchers then measured the ratio of two argon isotopes, Ar-40 and Ar-39, in the sand grains—a laborious process, since Ar-40 makes up about 99.5 percent of all argon found on Earth. Establishing the argon ratio allowed the researchers to use equations to determine the age of the surrounding sand grains. When Ar-40 is exposed to radiation, it decays to Ar-39; the remaining concentration of Ar-40 is measured, with higher Ar-40 concentrations indicating greater age. All tested grains are over 50 million years old. This puts the impact squarely in a geological period called the Paleocene.
The scientific community had previously believed that the impact occurred at the end of the Pleistocene 1 million years ago, when the Greenland ice sheet existed. However, new dating evidence for the study has established that the impact occurred during the Paleocene. The Paleocene (66-56 million years ago) is described as an orogenic period when the Earth was home to small herbivorous mammals and apparently lacked dinosaurs. At the time, Greenland was covered by temperate forests instead of the thick ice that now covers the entire impact area.
Just four years ago, the discovery of this crater was the product of a hunch. When Danish geologist Nicolaj Larsen studied detailed maps of Greenland, he noticed a circular structure beneath the glacier, prompting further investigation.He then picked a group of researchers, and they set out on the trek GreenlandThe crater they found was the first to be found under a continental ice sheet. In general, craters on Earth disappear quickly, and for those that persist, it’s often difficult to give an accurate age. Therefore, the accuracy of the argon dating under the Hiawatha Glacier is remarkable.
A previous study, published in 2018 Elizabeth Silber examined the likely timing of the Hiawatha impact before argon dating was available. Her main research goal is to determine whether the impact occurred before or during the Pleistocene, or last glacial period, 2,580,000 to 11,700 years ago. The work, done by Silber, a geoscientist at Western University in London, Ontario, paved the way for research in subsequent years.
Silber spoke with GlacierHub via email to discuss the challenges she faced during her research. she says”[the] The Hiawatha impact structure is somewhat mild relative to what we would expect from an aerial impact. ‘ Her statement indicated that the crater was shallow and that the peak ring had been damaged. Peak Ring Crater There are rings around the center of the crater. As a result, it is difficult to determine whether the crater’s structure is due to “preferential and slow erosion rates (if the crater formed when there was no ice sheet in the area), or whether the thick ice sheet absorbs some of the impact energy.” Both Both possibilities result in the crater having “less distinct morphological features.” The models used by Siber show that both scenarios (pre-Pleistocene or Pleistocene) are equally plausible, so the new study published using argon dating “is very exciting because this age estimate is consistent with our modeling results, pointing to older hit the structure,” Sieber said.
This raises the question: If the impact occurred much earlier than previously thought, how does this timing change alter its perceived impact on the global climate?Because initial age estimates placed the impact within the Pleistocene, it was previously thought that the impact may have been related to Young fairy tree cold period About 11,000 years ago. Younger Dryas was a period of extreme cooling, temporarily reversing the trend of global warming. It’s unclear what caused the event, but placing the Hiawatha impact 58 million years ago rules out any link between the two.
However, the impact occurred long before the Pleistocene, and it is unlikely that the impact would affect human life. More research is needed to pinpoint the exact effects, but given the size of the crater, it is likely that it had a considerable impact on the global climate. Many agree that the size of the meteorite alone would have thrown a lot of water vapor and debris into the atmosphere on impact, triggering a period of global cooling. In addition, the timing of the impact occurred within the time frame of the Paleocene carbon isotope maximum, when atmospheric carbon-13 levels peaked. The high carbon-13 values in the atmosphere provide further evidence that a giant meteorite impact can disrupt normal carbon-13 values.
As Liam Colgan told GlacierHub, it’s important to understand how ice behaved in previous periods to better understand their current impact. Colgan is a climatologist and editor Journal of Glaciology Focus on glaciers as indicators of climate change. He has nothing to do with recent research. “What happened in the past, still affects the ice sheet today,” he said. The properties of the Last Glacial (or Pleistocene) ice were very different from those of today’s Holocene ice. “
According to Colgan, understanding the depth at which ice from the last ice age transitioned to the more recent Holocene ice is critical to predicting ice behavior, a key issue in predicting future sea level rise. The resulting topographic differences may have influenced the ice movement seen today, although recent studies place the effects in the Paleocene.
Sand sampling using glacial meltwater, as well as argon dating, has been a great success in the study of remote and difficult terrain. These strategies can be applied to current crater analyses, allowing us to better understand Earth’s history and how to better predict the impact of future events.
