Stac Fada

April Editorial      


The largest meteorite in British Isles uncovered.


The largest to meteorite hit the British Isles has had to wait about 1.2 billion years to be discovered. Its existence was eventually brought to light during field work in 2006, but it took two years for analysis of the samples to show scientists what they were looking at. The brightly coloured rocks and rare minerals are well known near the Stoer Peninsula in Scotland where the meteorite came down, but these were thought to be of volcanic origin. However, the volcanic theory always had one, somewhat major, flaw - there is no record of volcanic activity past or present in the area and no volcanic vents or other volcanic sediments nearby.

The researchers from Oxford and Aberdeen Universities who investigated the impact site were working on a joint project led by Ken Amor of the University of Oxford. They spent two years painstakingly analysing the samples collected from the mountain Stac Fada, and their results have been published in the journal Geology. These results clearly point to an outer-space origin of the samples. Chemical analysis revealed evidence of what is known as an "ejecta blanket". This is debris which was thrown out when the huge projectile slammed into the Earth's crust. The rocks of the area show a high level of the key element iridium, which is generally found in low concentrations in rocks native to planet Earth. Additional microscopic studies of the rock surface showed the tell-tale microscopic parallel fractures which once again indicate a meteorite strike. According to Scott Thackrey, a PhD student in Geology and Petroleum Geology at the University of Aberdeen: "The type of ejected deposit discovered in North West Scotland is only observed on planets and satellites that possess a volatile rich subsurface, for example, Venus, Mars and Earth. Due to the rare nature of these deposits, each new discovery provides revelations in terms of the atmospheric and surface processes that occur round craters just after impact."

But the recent research not only suggests that there was a meteorite strike in British Isles, 1.2 billion years ago, but also that the meteorite was huge. The scientists estimate that the area of "ejecta blanket" is about 50 km across. They believe that the massive impact melted rocks and threw up a huge cloud of vapour that scattered material over a large part of the region around Ullapoo. It is suspected that the crater itself is to be found under the Minch, the waterway that separates Lewis in the Outer Hebrides. Just after the impact, the crater would have been huge, but Ken Amor explains it was rapidly buried under sandstone. This which makes the crater invisible, but at the same time, it preserved the meteoritic material for millions of years.

The evidence accumulated by Oxford and Aberdeen group definitely points to this being the largest meteorite strike known in the British Isles. The UK's only other known space impact location is Silverpit in the North Sea, about 130 km east of the Yorkshire coast, where scientists found evidence on the sea floor of a cataclysmic asteroid or comet strike that occurred some 60-65 million years ago.


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