Wilkes Land crater
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Wilkes Land crater is an informal term that may apply to two separate cases of conjectured giant impact craters hidden beneath the ice cap of Wilkes Land, Antarctica. These are separated below under the heading Wilkes Land anomaly and Wilkes Land mascon (mass concentration), based on terms used in their principal published reference sources.
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[edit] Wilkes Land anomaly
A hypothetical giant impact crater beneath the Wilkes Land ice sheet was first proposed by RA Schmidt in 1962, based on geophysical data[1]. He further considered the possibility that it might be the elusive source of tektites from the Australasian strewnfield. The hypothesis resurfaced in a paper by JG Weihaupt in 1976[2]. Evidence cited included a large negative gravity anomaly coincident with a supposed subglacial topographic depression 243 km across and having a minimum depth of 848 m. The claims were comprehensively refuted by CR Bentley in 1979 based on new airborne radio-echo sounding data that showed no evidence for the supposed crater[3].
[edit] Wilkes Land mascon (mass concentration)
The Wilkes Land mascon (mass concentration) is centered at and was first reported at a conference in May 2006 by a team of researchers led by Ralph von Frese and Laramie Potts of Ohio State University[4],[5]. The team used gravity measurements by NASA's GRACE satellites to identify a 300 km (200 mi) wide mass concentration and noted that this mass anomaly is centered within a larger ring-like structure visible in radar images of the land surface beneath the Antarctic ice cap. This combination suggested to them that the feature may mark the site of a 500 km (300 mi) wide impact crater buried beneath the ice.
Due to the site's location beneath the Antarctic ice sheet there are no direct samples to test for evidence of impact. There are alternative explanations for this mass concentration, such as formation by a mantle plume or other large-scale volcanic activity[citation needed]. If this feature really is an impact crater, then, based on the size of the ring structure, it has been suggested by von Frese's team that the impactor could have been four or five times wider than the one that created the Chicxulub Crater, believed to have caused the Cretaceous-Tertiary extinction event[5].
Because mass concentrations on Earth are expected to dissipate over time, von Frese and coworkers believe the structure must be less than 500 million years old, and also note that it appears to have been disturbed by the rift valley that formed 100 million years ago during the separation of Australia from the Gondwana supercontinent[5]. These researchers therefore speculate that it is possible that the putative impact and associated crater contributed to this separation by weakening the crust at this location. These bracketing dates also make it possible that the site could be associated with the Permian-Triassic extinction event[5]. The Permian-Triassic extinction occurred 250 million years ago, and is believed to be the largest extinction event since the origin of complex multicellular life. However, there are already other suggested candidates for giant impacts at the Permian-Triassic boundary, for example Bedout off the northern coast of Western Australia, although all are equally contentious, and it is currently under debate whether or not an impact played any role in this extinction.
[edit] References
- ^ Schmidt RA (1962). "Australites and Antarctica". Science 138 (3538): 443-444. Abstract.
- ^ Weihaupt JG (1976). "The Wilkes Land anomaly: Evidence for a possible hypervelocity impact crater". Journal of Geophysical Research 81 (B32): 5651-5663. Abstract.
- ^ Bentley CR (1979). "No giant meteorite crater in Wilkes Land, Antarctica". Journal of Geophysical Research 84 (Sept. 10): 5681-5682. Abstract.
- ^ von Frese RR, Potts L, et al (2006). "Permian-Triassic mascon in Antarctica". Eos Trans. AGU, Jt. Assem. Suppl. 87(36): Abstract T41A-08. Abstract.
- ^ a b c d Gorder, Pam Frost (June 1, 2006). Big Bang in Antarctica – Killer Crater Found Under Ice. Ohio State University Research News.
[edit] External links
- Images of crater area via Ohio State University
- Giant Crater Found: Tied to Worst Mass Extinction Ever Robert Roy Britt (SPACE.com) 1 June 2006 06:07 p.m. ET
- Giant meteor spawned Australian continent, scientists say AFP (ABC.net.au) 3 June 2006. 07:21 a.m. (AEST)
- Does a giant crater lie beneath the Antarctic ice? Nature.com, 2 June 2006.
