The idea that such a structure lies between the Western Isles and mainland Scotland was first raised back in They found evidence on the Highlands coast for the rocky debris that would have been produced by a giant impact.
Now, the team from Oxford and Exeter universities believes it can pinpoint where the space object fell to Earth. The feature would be buried deep under the seafloor, they add.
It's an intriguing prospect. The evidence gathered so far suggests the event occurred about 1. The key supporting evidence is a group of reddish-coloured rocks on the eastern side of The Minch known as the Stac Fada deposit. These are determined to be ejecta from the impact - the material hurled outwards when a km-wide object slammed into what was probably then some kind of rift valley.
The rocks are fragmented and contain melt particles, and also what geologists term shocked quartz - a type of mineral that has at some point been subjected to enormous pressures. Even with just that brief glimpse, we can already say a lot about this crater. The resulting explosion almost always creates a circular depression regardless of the original impact angle with a raised rim and ejecta blanket that thins out the further away you get.
The dimensions of the crater — its diameter, the depth to the floor, the height of the rim — are not random, but closely related to each other and the total energy of the impact. First, as my dad noted, the outer walls are very steep and rugged. He estimated the depth-to-diameter ratio as about , which is much more exaggerated than any real impact craters on the Earth or Moon, which have depth-to-diameter ratios closer to Or an impact crater!
Making a detailed comparison between the volcanoes of the Earth and the craters of the Moon, Gilbert made a case for the impact hypothesis instead, concluding:.
Ninety-nine times in one hundred the bottom of the lunar crater lies lower than the outer plain; ninety-nine times in a hundred the bottom of the Vesuvian crater lies higher than the outer plain.
Ordinarily the inner height of the lunar crater rim is more than double its outer height; ordinarily the outer height of the Vesuvian crater rim is more than double its inner height. The lunar crater is sunk in the lunar plain; the Vesuvian is perched on a mountain top…Thus, through the expression of every feature the lunar crater emphatically denies kinship with the ordinary volcanoes of the earth.
Iron meteorites, like this one, are pretty alien looking. Meteor Crater in Arizona, 50, years old. Posted in Reflections. November 24, at pm. Meg says:. November 25, at am.
Strangways says:. November 30, at pm. Located in the desert of Arizona, USA , it's actually the only such impact crater that looks like the ones on the moon. So, strictly speaking, this may not actually be prototypical of the craters on Earth, but nevertheless it looks so dramatic that it's become an icon, the most recognizable shape of its sort.
It's been turned into quite a commercialized tourist attraction, with a rather oversized visitor centre, museum, cinema, offers of guided walks along the crater rim and an extensive souvenir shop. More background info: The impression of the crater is that it's indeed big — it's nearly a mile 1. The reason it hasn't eroded much — hence its moon-like appearance — is the fact that it is relatively young and that it lies in the middle of a dry desert. Other, much bigger impact craters around the world do not usually look anything like the moon's craters because they're older and vegetation and all kinds of erosion has changed their appearance so much that it is often not even an easy task identifying them.
The Barringer Crater, however, was formed "only" ca. The meteor ite that created the Barringer Crater consisted of nickel-iron weighing ca.
Fragments of it were found up to 10 miles 15 km from the crater. It's believed to have been ca. Combined with the impact speed, the force it had must have been the equivalent of well over one hundred Hiroshima bombs or that of one larger H-bomb.
Technically speaking it should have more correctly been called Meteorite Crater, though, not Meteor Crater — as 'meteor' is the term for such pieces of rock as long as they're in space; when they fall to Earth or onto any other heavenly body's surface the term meteorite applies. But anyway ….
The crater got its name from one Daniel Barringer, who in the early 20th century came to study the site and dig for the iron!
He was the first to propose the theory that it may have been caused by the impact of a meteorite from space. Before, it had naturally been assumed that it was of volcanic origin — which made sense, since undeniably volcanic crater formations can be found not far away in the San Francisco mountain range.
Barringer's impact theory long remained controversial, in fact it was largely rejected, until only relatively recently.
Only from the s did it finally become the universally accepted theory within the scientific community. One person who was instrumental in this shift in acceptance of Barringer's proposal was Eugene Shoemaker, who is best known for the joint discovery of the Shoemaker-Levy-9 comet.
Its fractured pieces dramatically collided with Jupiter in — giving scientists the first chance of observing such an event in the solar system "live". He found that certain mineral formations also present in the Barringer Crater could only have been created by a kind of sudden shock compression that could not be the result of volcanism … but that did occur e.
A prime example is the Sedan Crater at the NTS, which was formed as part of Operation Ploughshare, a test series intended to explore the possibilities of using atomic bombs for civil engineering earth-movement purposes.
And the similarities between the Sedan and Barringer Craters are immediately striking. With the geochemistry confirming a similar sudden-shock origin for both craters, only the meteorite impact theory for Barringer's Crater was left as the sole plausible explanation for its creation. It has since been corroborated by all manner of other evidence and no doubt about it now remains.
It may be far from being as big as some of the older impact craters on Earth, but because it is so young and hardly eroded at all, it is unique in its nearly pristine appearance as a prototypical moon-like crater. In fact, because of its similarity to the craters on the surface of the moon, the Barringer Crater was used by Apollo astronauts in training for their lunar missions.
Today, the site, still owned by the Barringer family, is heavily commodified for tourism though scientific research is also still conducted here — and this includes quite a lot of dramatization to "sell" the story of meteorites and impacts in general to a public that is clearly eager to "buy" this.
The Barringer Crater is actually included here as a dark tourism site simply for the reason that it gives visitors a dramatic impression of what forces are released by even such a relatively small meteorite.
The next question, therefore, immediately crops up: what if a much bigger one were to collide with planet Earth?
Could it wipe out civilization or even humankind in its entirety? Given such horror scenarios, meteorite collisions have become a popular theme of disaster movies and sci-fi stories. That's what ultimately makes a crater such as Barringer a "dark" site too — even though it cannot have caused any human deaths at the time humans only began arriving in the Americas much later , but was "only" a disaster for the flora and fauna around the site back then.
But since it is the best preserved and most dramatic looking impact crater on Earth, it's been chosen here to represent the entire dark issue of potentially disastrous collisions of meteor ites with our planet. What there is to see: other than the big hole itself, not all that much, even though the Barringer Meteor Crater Company tries hard to supplement the crater by means of an exhibition, a film, talks, tours and, especially, a huge shop.
First you have to ascend the stairs or be lazy and take the lift up the crater rim level. From the entrance it's another ascent up a long corridor before you get to the crater rim viewing points. You can view the crater from the shielded and air-conditioned interior through large windows, or you can step outside for a clear and unobstructed view of the big hole in the open air.
0コメント