have been a comet or asteroid about across, with a mass of about . An object across smashing into the sea at many kilometers per second would generate enormous tsunamis. Scientists are currently searching for any evidence of large tsunamis in the surrounding areas dating from around that time, but no such evidence has been uncovered yet. Age The position of the crater within the layers of rock and sediment on the sea floor could in theory be used to constrain its age: sediments laid down before the crater's formation might conceivably be disturbed by the impact, while those laid down afterwards will not. In their discovery paper, Allen and Stewart stated that Silverpit was formed in Cretaceous chalk and Jurassic shale, but is covered by an undisturbed layer of Paleogene sediment. The Cretaceous Period ended about 66 million years ago, but, on the evidence of nearby boreholes, the lowermost Paleogene sediments appear to be absent. Thus the age of the Silverpit event was initially stated to lie somewhere between 66 and 60 million years before present. However, after a more detailed appraisal of the seismic data, Allen and Stewart gave a more cautious estimate of the age as between 74 and 45 million years (Late Cretaceous – Eocene). The stratigraphic method of estimating the age of a crater is somewhat crude and imprecise, and the result is questioned by Underhill's non-impact hypothesis. Assuming an impact origin, other possible ways of dating the event include looking for evidence of ejecta material such as tektites, and deposits from the hypothesised tsunami, which might be found anywhere around the North Sea basin. As well as allowing a more accurate age determination, finding such evidence would also strengthen the impact hypothesis. Two nearby oil exploration wells penetrate the ring system, yet cutting samples from these fail to provide any independent support for the meteor theory, thus weakening the case for it being due to an extraterrestrial body. Analysis of samples taken directly from the central crater would also assist age determination as well as confirm one or other of the proposed theories; until this has occurred Silverpit cannot be confirmed as an impact structure. Multiple Impact Hypothesis The early estimate of the age of the Silverpit event, stated as 66–60 million years before present, overlaps with the age of the Chicxulub impact near the northwest corner of the Yucatan Peninsula, which occurred 66