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Charles Carrigan
14,778 followers -
Husband, Father, Geoscientist, Educator
Husband, Father, Geoscientist, Educator

14,778 followers
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Cool Contact

When hot magmas intrude into older, cold rocks, they freeze fairly quickly on their margins. As a result, they are finer-grained right next to the contact, and coarser-grained inside this thin rind. Here a pink-white-gray granite (lower left) intruded a greenish gray rhyolite (upper right) and developed this texture quite nicely. The minerals in the granite such as K-feldspar (pink), plagioclase (white), and biotite (black) are all much smaller in size at the contact with the old volcanic rock. This feature is called a chilled margin, and it allows us to determine which rock of the two is the youngest, and which is the oldest. In this case, the granite is younger and the rhyolite is older. By using clues such as these, geologists put rocks in a sequence and determine their relative histories.

#MagmaMonday #Igneous #StFrancoisMountains #granite #rhyolite #geologyrocks 
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#FridayFold - Small, inclined open folds in silver-gray phyllite from near Devil's Lake State Park, WI.

#GeologicStructure #Science #Nature #Phyllite #DevilsLake #Baraboo

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Meanwhile, the amount of CO2 added to the atmosphere in the past 2 years hit record levels of 3 ppm added per year. In the 1960s, we were only adding about 1 ppm net CO2 per year to the atmosphere. 

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Scientific Organizations and Their Statements on Climate Change

The scientists are screaming it as loud as possible. There are many, however, who simply are refusing to hear it and pretend that it still "needs debate" or that it "isn't settled".

And then the same folks turn around and reduce funding for the organizations that are doing the research, because apparently even if it truly isn't settled we don't need to know anyway. 

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Fossil Meteorite with Cephalopod at the Field Museum

Meteorites that are found have generally fallen out of the sky in the not to distant past. That doesn't mean that they haven't fallen throughout Earth's history, of course, and old meteorite impact sites are well known in the rock record. But the meteorites themselves that fell millions of years ago are pretty rare, because they weather away fairly easily at Earth's surface. A few, however, have been preserved in the ancient rock record as "fossil" meteorites. This one on display at the Field Museum is preserved in a Devonian limestone. The weathering rind is pretty thick, even being encased in the limestone. Some minerals in meteorites, like the spinels, are much less susceptible to weathering and last longer than the olivine, iron, and pyroxenes that dominate chondrites. This one is also special in that it also preserves a beautiful, large cephalopod.

#Geology #Paleontology #Meteorites #FieldMuseum #Science #Nature 
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#FridayFold today is from the Black Hills of SD

The Black Hills expose an old Precambrian area of metamorphic rocks that are complexly deformed. They were brought to the surface relatively recently during the same mountain building event that uplifted the Rocky Mountains much farther to the West. These thin layers are bent back on themselves so much that if you didn't see the hinge you'd have a hard time knowing they were even folded. Since both limbs of the fold would measure at the same angle, this kind of fold is called isoclinal.

#GeologicStructure #Science #Nature #OptOutside #PostMoreRocks #Geology 
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Feb. 2017 was the 2nd warmest Feb ever directly measured, in 137 years.

This wouldn't be news IF the number of cold records being broken were anywhere close to the number of warm records. But warm records just keep getting broken, year after year, month after month, region after region. The pattern of warming is undeniable.

https://data.giss.nasa.gov/gistemp/news/20170315/

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New Sm-Nd isotope data from really old Canadian rocks (~2.7 Ga) suggest that they formed from a precursor rock that would have been extremely old >~4.3 Ga basaltic crust. If so, that basaltic crust would have sat around on the Earth's surface for an extremely long time, suggesting therefore that plate tectonics did not exist in the early history of the Earth.

https://www.sciencenews.org/article/remnants-earths-original-crust-preserve-time-plate-tectonics

If you want the Science article, it is here: http://science.sciencemag.org/content/355/6330/1199
Abstract: "Geologic processing of Earth’s surface has removed most of the evidence concerning the nature of Earth’s first crust. One region of ancient crust is the Hudson Bay terrane of northeastern Canada, which is mainly composed of Neoarchean felsic crust and forms the nucleus of the Northeastern Superior Province. New data show these ~2.7-billion-year-old rocks to be the youngest to yield variability in neodymium-142 (142Nd), the decay product of short-lived samarium-146 (146Sm). Combined 146-147Sm-142-143Nd data reveal that this large block of Archean crust formed by reworking of much older (>4.2 billion-year-old) mafic crust over a 1.5-billion-year interval of early Earth history. Thus, unlike on modern Earth, mafic crust apparently could survive for more than 1 billion years to form an important source rock for Archean crustal genesis."

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Remnants of the Ice Age

The Grand Tetons are currently home to a single remaining glacier, but in the past there were quite a few. Here the upper bowl (called a cirque) between the high peaks, where ice would have accumulated, is still visible, with snow covering it and the glacial valley below. However, by summer's end, this one will not retain enough ice to accumulate mass on an annual basis, and so the yearly snows temporarily fill what was once a continually flowing mass of ice.

#Geology #Nature #IceAge #Science #ScienceEducation #Glacier #GrandTetons 
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TouchTerrain is a new web app that is a super easy way to find an area of the world and get a file created that can be used in a 3D printer in order to replicate topography. 
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