21 Sep 2017

This link has been sent in by both William and Gary. At https://phys.org/print424941552.html ... a paper published in the journal Earth and Planetary Science Letters claims that an impact crater in Canada produced the highest temperatures ever recorded on the planet;s surface. There is of course a lot of hype in that headline as this is the only instance energy produced heat has been measured in such a way - and other craters may yield temperature gradients just as high. The reference is to a lake crater inLabrador, 28 km across. It is dated 38 million years ago. Mostly, comets and asteroids vapourise on impact (or in the atmosphere), even the rocks and material they strike on the ground. However, in this instance, the authors claim they have found a way to measure the heat generated by the impact, which is the result of the energy involved. Basically, they discovered zircon in the crater. The zircon had been changed into cubic zirconia - which requires temperatures of 2370 degrees Celsius. Hence, the headline is derived from this figure - nothing else. It means the impact generated that much heat and energy and in all likelihood exceeded that figure. See Nicholas Timms et al at http://DOI:10.1016/jepsl.2017.08.012

See also www.dailymail.co.uk/sciencetech/article-4896322/Asteroid-strike-caused-h... ... where we learn that zirconia is a diamond like stone - so how much heat does it require to make diamonds? Also found were glass like minerals - another sign of impact and heat generation. Crystals among zirconia grains show the phase transformation history of the crystal allowing them to trace back how they formed. Further, the impact dates to the Eocene period - long after the dinosaurs.