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. If this feature really is an impact crater then, based on the size of the ring structure, it has been suggested by Frese's team that the impactor could have been four or five times wider than the Chicxulub impactor, which is believed to have caused the Cretaceous–Paleogene extinction event. Because mass concentrations on Earth are expected to dissipate over time, Frese and his collaborators 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. The researchers, therefore, speculate that the putative impact and associated crater may have contributed to this separation by weakening the earth's crust at this location. These bracketing dates also make it possible that the site could be associated with the Permian–Triassic extinction event. 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. Plate reconstructions for the Permian–Triassic boundary place the putative crater directly antipodal to the Siberian Traps, and Frese et al. (2009) use the controversial theory that impacts can trigger massive volcanism at their antipodes to bolster their impact crater theory. However, there are already other suggested candidates for giant impacts at the Permian–Triassic boundary, such as 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. The complete absence of a well-defined impact ejecta layer associated with the Permian–Triassic boundary at its outcrops within Victoria Land and the central Transantarctic Mountains argues against there having been any impact capable of creating a crater the size of the hypothesized Wilkes Land impact crater within Antarctica at the Permian–Triassic boundary. Nonetheless, according to Frese, recent studies in 2018 seem to sustain the impact origin of crater, and the event may be linked to the separation of Eastern Antarctica from southern Australia. See also Bedout Chicxulub crater Cretaceous–Paleogene extinction event List of possible impact structures on Earth Permian–Triassic extinction event Siberian Traps Vredefort impact structure References External links (2006) Images of crater area via Ohio State University (archived