Huge asteroid slammed into Greenland just a few million years after the dinosaurs died out

Jan 27, 2020
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Space.com

It's much, much older than originally anticipated.

by Stefanie Waldek, 22 days ago

hiawatha crater.jpeg
The Hiawatha impact crater in Greenland, as depicted by NASA's Scientific Visualization Studio. (Image credit: NASA)

Hidden under Greenland's thick ice sheet, scientists found what they thought was the scar of an asteroid impact perhaps just thousands of years old, fresh enough that humans were already on the scene.

But after several years of additional research, two separate teams of scientists have determined its age to be far older: 58 million years. Researchers from the University of Copenhagen's GLOBE Institute discovered the structure, which they suspected to be a massive 20-mile-wide (31 kilometers) impact crater, in 2015 beneath Greenland's thick Hiawatha ice sheet.

In the new research, scientists at the Natural History Museum of Denmark and the GLOBE Institute at the University of Copenhagen in the same country sampled sand from the Hiawatha crater and heated it, using the argon gas released from the grains to date the impact event. Simultaneously, researchers from the Swedish Museum of Natural History independently sampled rocks from the crater and dated them using the uranium fingerprint of the mineral zircon, according to a statement from the University of Copenhagen. Both teams settled on the 58-million-year-age.

"Dating the crater has been a particularly tough nut to crack, so it's very satisfying that two laboratories in Denmark and Sweden, using different dating methods, arrived at the same conclusion. As such, I'm convinced that we've determined the crater's actual age, which is much older than many people once thought," Michael Storey, a scientist at the Natural History Museum of Denmark, said in a statement.

At the time the researchers have pinpointed, Greenland was not covered in an ice sheet, but rather was home to a temperate rainforest. When the asteroid that created the crater impacted Earth, it did so with a force estimated to be several million times stronger than that of an atomic bomb. While that impact certainly would have annihilated a large part of Greenland, scientists are not sure of the impact's effect on global climate.

That uncertainty is in contrast to the most famous asteroid impact, which formed the Chicxulub crater in Mexico and eradicated most of the dinosaurs 66 million years ago, just a few million years prior to the Greenland impact. The Chicxulub crater is nearly 6.5 times larger than Hiawatha.

The scientists plan to continue to study the Hiawatha crater in hopes of understanding its effect, on both a local and a global scale.

A paper describing the research dating the Hiawatha impact crater was published Wednesday (March 9) in the journal Science Advances.

Follow Stefanie Waldek on Twitter @StefanieWaldek. Follow us on Twitter @Spacedotcom and on Facebook.

See: https://www.space.com/greenland-impact-crater-hiawatha-age

A late Paleocene Age for Greenland's Hiawatha Impact Structure (Partial below)
SCIENCE ADVANCES • 9 Mar 2022 • Vol 8, Issue 10 • DOI: 10.1126/sciadv.abm2434
By Kevin G. Kenny, William R. Hyde, et al

The ~31-km-wide Hiawatha structure, located beneath Hiawatha Glacier in northwestern Greenland, has been proposed as an impact structure that may have formed after the Pleistocene inception of the Greenland Ice Sheet. To date the structure, we conducted 40Ar/39Ar analyses on glaciofluvial sand and U-Pb analyses on zircon separated from glaciofluvial pebbles of impact melt rock, all sampled immediately downstream of Hiawatha Glacier. Unshocked zircon in the impact melt rocks dates to ~1915 million years (Ma), consistent with felsic intrusions found in local bedrock. The 40Ar/39Ar data indicate Late Paleocene resetting and shocked zircon dates to 57.99 ± 0.54 Ma, which we interpret as the impact age. Consequently, the Hiawatha impact structure far predates Pleistocene glaciation and is unrelated to either the Paleocene-Eocene Thermal Maximum or flood basalt volcanism in east Greenland. However, it was contemporaneous with the Paleocene Carbon Isotope Maximum, although the impact’s exact paleoenvironmental and climatic significance awaits further investigation.

sciadv.abm2434-f1.hiawatha.jpeg
FIG. 1. Location and geomorphological setting of Hiawatha Glacier, northwest Greenland.
(A) Regional view of northwest Greenland. (B) Bedrock topography map showing the Hiawatha structure, and sampling locations of glaciofluvial sediment for 40Ar/39Ar analysis (HW21-2016) and clasts of impact melt rock for zircon U-Pb analysis (HW19-01 and HW19-05). Bed topography based on NASA and 2016 Alfred Wegener Institute (AWI) airborne radar-sounding data. Samples HW19-01 and HW19-05 are from the same location on a wide riverbank 4 km downstream of the terminus of Hiawatha Glacier. White line represents the present-day margin of the Greenland Ice Sheet. Figure was modified after (1).


To contextualize an impact structure within the geologic record requires precise knowledge of its age, but available age constraints for the Hiawatha structure are only tentative. The bedrock under the structure is likely a continuation of the highly metamorphosed 1.95– to 1.75–billion year (Ga) (4) bedrock of the Ellesmere-Inglefield mobile belt that is exposed in Inglefield Land immediately adjacent to Hiawatha Glacier, which provides a maximum constraint on the structure’s age (1). Further age estimates have been based on indirect constraints, such as estimates of erosion rates in Greenland and the structure’s apparent relationship to the Greenland Ice Sheet (1). The structure has a rim-to-floor depth of 320 ± 70 m and a dissected central uplift that is up to 50 m high and whose peaks are up to ~8 km apart (1). The depth of the structure and the height of the central uplift are muted compared to that predicted for a fresh, subaerial terrestrial crater of the same diameter (predicted depth of ~800 m) (5). This could result from slow erosion over a long period or faster erosion over a shorter period. Reported fluvial and subglacial erosion rates spanning a range of ~10 to 10,000 m million years−1 (Ma−1) (~10−5 to 10−2 m year−1) (69) mean that the ~500-m erosion of the crater rim corresponds to a minimum period of erosion of ~50 thousand years (ka) and a maximum period of ~50 Ma (1). Radar evidence of active subglacial erosion at present and active sediment deposition at the glacier front were interpreted to favor a faster subglacial erosion rate and hence potentially a younger age (1). Anomalous radiostratigraphy of the ice of Hiawatha Glacier relative to the rest of the Greenland Ice Sheet was interpreted to have potentially resulted from an impact through thick ice or subsequent impact-related heating affecting ice flow (1), also provisionally suggesting an impact after the 2.6-Ma (10) inception of the Greenland Ice Sheet.

Given the tentative nature of these previous age constraints, here, we undertake dating of the structure using detrital materials sampled immediately downstream thereof. We report both 40Ar/39Ar analysis of the impact-related glaciofluvial sand previously described in (1) and U-Pb analysis of shocked zircon from recently collected, and previously unreported, pebble-sized glaciofluvial clasts of impact melt rock.

However, the Late Paleocene age reported here naturally explains the structure’s muted morphology as a result of long-term erosion, with its rim and porous peak ring (21) having been preferentially eroded, as well as the absence of impact ejecta in Greenland’s Pleistocene rock and ice records. Moreover, the age indicates that since 58 Ma mean erosion rates in this area of northwestern Greenland have been at the lower end of the reported range considered in (1). If we assume that the crater’s present rim-to-floor depth of 320 ± 70 m reflects ~500 m of erosion, this corresponds to a mean erosion rate of less than 10 m Ma−1. However, as the structure has not been drilled, it is not certain to what degree its present morphology reflects differential erosion across the feature or sediment infill of the crater floor, and the erosion rate remains an approximation only and likely an upper bound. Despite its imprecision, this relatively low erosion rate for a major subglacial structure in northwestern Greenland has important implications for the understanding of other major subglacial geomorphological features found beneath the ice sheet in recent years, including large valleys (2224), a second possible impact structure (25), and a fault-bounded lake (26). These other features may thus also be older than previously assumed and unrelated to the inception of the Greenland Ice Sheet. In particular, slower erosion suggests that large subglacial valleys represent a long-lasting river system that delivered sediments offshore since the Mesozoic Era, and that they only were reshaped by glacial erosion during the Pliocene and Pleistocene epochs (27).

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See: https://www.science.org/doi/10.1126/sciadv.abm2434

The fascinating exploration and dating of a late Paleocene crater in Greenland. And it turns out that this impact happened after the incredible blast on the Yucatan Peninsula which created the Chicxulub Crater and helped end the rule of the dinosaurs. The investigators of the Hiawatha crater have also found that the impact occurred after the inception of the Greenland ice cap.
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