New answers tagged geology
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Flint nodules, like opal nodules and geodes, are formed in chalk and limestone. These rocks are made of calcium carbonate from the skeletons of trillions of marine micro-organisms which lived many millions of years ago and sank to form sediment on the sea bed. This sediment was compressed to form chalk and limestone as millions of years went by. Among the ...
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A 5km impactor would make a very, very global mess.
Here's a discussion of tsunami formation from asteroid impacts. It presents numbers for impactor size up to 2km, and posits a rule-of-thumb that indicates a 5km impactor would generate a coherent wave (one that doesn't dissipate much over great distances) as long as it impacts in water less than 20-30km ...
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That seems way too low, even for crustal rocks. Recall: Vp = sqrt[(K + 4G/3)/𝜌]
If you have a rough idea of the mineralogy of the rock (you do if you know that it's andesite or rhyolite), you can estimate the bulk modulus (K) and shear modulus (G) with a Voigt-Reuss-Hill average and use a reasonable density value (maybe 2500 kg/m^3) to get a reasonable ...
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I'm almost sure that what you have is a fossil tortoise, but it would be interesting to see further photos of it from different angles. Another time, bear in mind the information requirements and give as much info about the specimen as you can. I saw a photo of one advertised as a fossil tortoise from Morocco, so it would be interesting to know where yours ...
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From your detailed description and well-focused photos, I am struck by how similar your specimen is to a specimen that I found and had identified as being "lead ore", which was a very general description. Specifically, my specimen was a rock composed of several types of sulfides (mostly Pb and some Ag) with minor accessory oxides (Fe). Your close-up photo ...
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I don't think neutrinos will be much good for mapping the interior of the Earth, the reason being that they rarely interact with matter and are said to be able to pass through 11 light years of solid lead without being stopped (though I would take that claim with a pinch of salt). However, so many pass through the Earth from the other side that a tiny ...
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Near to the Earth's surface there are small variations in the Earth's magnetic field, but these don't play a role in providing the magnetosphere which protects the Earth from charged particles emanating chiefly from the solar wind.
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If you extend your map out a little bit further, you will see that the Brooks Range is just a continuation of the Rocky Mountains into Alaska.
Source: freeworldmaps.net, ©Daniel Feher (explicitly permitted use here)
The Brooks Range was formed at the same time as the front ranges of the Rockies in Canada and the Lower 48, during the Laramide Orogeny ...
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You almost got the answer yourself. The rock is definitely lignite. As a confirmatory test, you could scorch it with a blow lamp or put it on a fire. If it's lignite it will burn.
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These globular structures are called varioles, and there is not complete agreement as to how they are formed. The most likely theory is that the basalt has been hydrothermically altered by millions of years of water infiltration bringing in tiny amounts of other minerals, but the jury is still out.
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Your rock is granite, an igneous rock of volcanic origin, not sedimentary. It has a similar composition to basalt, but has cooled more slowly and therefore has larger crystals. It is mostly made of quartz, which is usually white, feldspar. mica and hornblende. Hornblende is black, though there are other minerals sometimes found in granite which are also ...
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Oceans did form on other rocky planets - at least Venus and Mars, and moreover, many moons of Jupiter and Saturn as well.
The problem is that of the two other terrestrial "uberplanets" who had oceans - i.e. the aforementioned Venus and Mars - they lost them, but in rather different ways.
On Venus, what happened appears to have been that, synthesizing the ...
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You are entirely correct. Todd and Engi write:
The mineral assemblages of rocks at the surface lie on a locus of
P–T-conditions… It must be stressed…does not imply a P–T-distribution or geotherm realized at any one time during the orogenic evolution of this area. Even assuming the P–T-values
reflect maximum metamorphic conditions, these were ...
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