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A pioneer in the use of tephra layers as marker horizons to establish chronology was [[Sigurdur Thorarinsson]], who began by studying the layers he found in his native Iceland.<ref>Alloway et al. (2007)</ref> Since the late 1990s, techniques developed by Chris S. M. Turney ([[QUB]], Belfast; now [[University of Exeter]]) and others for extracting tephra horizons invisible to the naked eye ("cryptotephra")<ref>Turney et al. (1997)</ref> have revolutionised the application of tephrochronology. This technique relies upon the difference between the specific gravity of the microtephra shards and the host sediment matrix. It has led to the first discovery of the Vedde ash on the mainland of Britain, in Sweden, in [[the Netherlands]], in the Swiss Lake [[Soppensee]] and in two sites on the [[Karelian Isthmus]] of Baltic Russia.
It has also revealed previously undetected ash layers, such as the Borrobol Tephra first discovered in northern [[Scotland]], dated to ca. 14.4 cal. ka BP,<ref>Turney et al. (1997)</ref> the microtephra horizons of equivalent geochemistry from southern [[Sweden]], dated at 13,900 Cariaco varve yrs BP<ref>Davies (2004)</ref> and from northwest Scotland, dated at 13.6 cal. ka BP.<ref>Ranner et al. (2005)</ref>