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History of the Earth

We"ve concentrated the history of Planet Earth into one year. Follow the geology podcasts chronologically from the origin of the Earth to the origin of Mankind.

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Cone-in-Cone

History of the Earth ·

2019/05/30

The mineral here is just calcite (even though it’s mostlyalmost black), but it shows interesting features. Cone-in-cone structures are nested cones, seen here in cross section. The inset shows them a little better – in the main photo, they are represented by very narrow vertical triangles. It’s not certain how these things form, but some kind of systematic displacement because of microscopic crystal growth variations is probably the favored idea. The variations might be because of clay

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The Llanite Dike

History of the Earth ·

2019/05/27

Mineral Monday + Tectonic Tuesday. Blue quartz is uncommon and is usually colored by inclusions of unusual minerals like crocidolite, tourmaline, or dumortierite. The purplish-blue quartz here, from north of Llano, Texas, is colored by inclusions of ilmenite (iron-titanium oxide). This rock is called llanite for its occurrence in the Llano Uplift of central Texas, and although similar rocks are found in other parts of the world, the variety name llanite really only applies to this location. On a

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History of Geology: Recognizing overthrusts

History of the Earth ·

2019/05/21

Middle section of the 38-inch cross-section Cover This Tectonic Tuesday is also an example of the History of Geology. “The thrust producing these crustal movements and dislocations came from the west, and must have been highly energetic in its action, as some of the breaks are of huge proportions, and are accompanied by displacements of many thousands of feet. The faulted region is now about twenty-five miles wide, but a rough estimate places its original width at over fifty miles, the

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Epitaxy

History of the Earth ·

2019/05/19

Epitaxy, from Greek words meaning “upon” or “above” and “ordered arrangement,” in minerals means crystals of one (or the same) mineral growing in a particular crystallographic position on another (or the same) mineral. It happens because the molecular spacings and orientations happen to be similar, allowing, even encouraging the crystal structure of the second, later mineral to mesh with that of the first. Some mineralogists might say that epitaxy requires the two minerals to be different

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An extension of the Mid-Continent Rift?

History of the Earth ·

2019/05/17

In the far northwest corner of the flat, flat Texas panhandle, extending into New Mexico, there’s a narrow, elongate magnetic low. The intensity of the anomaly – 250 nanoTesla or more – says it’s fundamentally the expression of a lithologic change rather than a structure; i.e. it represents something pretty strongly magnetic. Its long narrow geometry is that of a dike. And its negative value suggests that it’s reversely polarized, solidifying from magma during a time when the earth’s magnetic

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Thulite

History of the Earth ·

2019/05/15

Thule was the far north in Greek and Roman literature, often identified with Scandinavia. Thursday was named after Thor, the Norse god of thunder. Whether these pink minerals are orthorhombic thulite or monoclinic clinothulite would take analysis that I haven’t done, but either way they contain trivalent manganese to give the pink color. The white mineral that contains them is scapolite, specifically meionite (I HAVE had an x-ray analysis of it), a different calcium-aluminum silicate. The

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150 years of the Periodic table

History of the Earth ·

2019/05/14

2019 marks the sesquicentennial of Dmitri Mendeleev’s Periodic Table of the elements, which was not just an effective organizational scheme based on the atomic nature of the elements, but also a predictive tool regarding elements that had not yet been discovered in 1869. The validity of the Table was proven in 1875. Mendeleev had predicted the existence of several elements, including one he called eka-aluminum. “Eka” is Sanskrit for “one,” thus meaning the unknown element would be one period

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Artinite and the Coast Ranges of California

History of the Earth ·

2019/05/13

The mineral is artinite, a magnesium carbonate that is an alteration product of high-magnesium serpentinites of the Diablo Range in central California. It’s from New Idria, a mercury (and other) mining district named for the historic Idria mercury mines now in Slovenia, which have been mined since 1490. Tectonically, the New Idria area of California is in a fenster (German for window), a hole in a thrust sheet that is related to the collisions that produced the California Coast Ranges

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Fuchsite

History of the Earth ·

2019/05/12

Fuchsite is a chromium-bearing variety of the mica muscovite, K(Al,Cr)3Si3O10(OH)2 . Chromium gives the green color to the muscovite. This specimen was collected by Theresa Schwartz and given to me by Susan Vuke. Theresa reports it was a clast in a pediment near Little Antelope Valley, northwest of Harrison, Montana. That leaves the question open as to where it formed and came from, but a source in the Tobacco Root Mountains is most likely. The pediment gravel itself was probably deposited

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Timan-Pechora Basin

History of the Earth ·

2019/05/11

This is part of the magnetic map of the former Soviet Union. It reveals three continental blocks and their amalgamation to form part of Eurasia. The Siberian Craton (a craton is a strong, usually fairly old block of continental crust) collided with and became attached to the East European Craton beginning about 300 million years ago, about the same time as Europe and Africa began to collide with North America to form the Appalachians. Here, the collision produced the Ural Mountains (orogeny

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Barite with inclusions

History of the Earth ·

2019/05/10

Beginning with this post, the blog is "blog only" - no more podcasts, at least not for now. The brownest zones of barite in this example result from dense inclusions of deep reddish material, probably hematite, in blebs smaller than a hundredth of a millimeter barely visible in the image. The larger inclusions you can see here are brassy spheres, triangular prisms, and elongate pencils, and are probably pyrite but chalcopyrite is possible. The lower right inset shows the pencil forms a

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Episode 397 Carbonatites

History of the Earth ·

2018/04/30

Carbonatites are strange igneous rocks made up mostly of carbonates – common minerals like calcite, calcium carbonate. Igneous rocks that solidify from molten magma usually are high-temperature rocks containing lots of silicon which results in lots of quartz, feldspars, micas, and ferro-magnesian minerals in rocks like granite and basalt. Carbonatites crystallize from essentially molten calcite, and that’s really unusual. Most carbonatites are intrusive, meaning they solidified within the

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Episode 396 Turbidity currents

History of the Earth ·

2018/04/17

As near as I can tell in the original daily series in 2014, I never addressed the topic of turbidity currents and their sedimentary product, turbidites. But they account for the distribution of vast quantities of sediment on continental shelves and slopes and elsewhere. You know what turbid water is: water with a lot of suspended sediment, usually fine mud particles. In natural submarine environments, unconsolidated sediment contains a lot of water, and when a slurry-like package of sediment

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Episode 395 Connections

History of the Earth ·

2018/04/10

This episode is about some of the interesting connections that arise in science. We’ll start with me and my first professional job as a mineralogist analyzing kidney stones. My mineralogy professor at Indiana University, Carl Beck, died unexpectedly, and his wife asked me as his only grad student to carry on his business performing analysis of kidney stones. Beck had pioneered the idea of crystallographic examination to determine mineralogy of these compounds because traditional chemical

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Episode 394 The Mangrullo Formation of Uruguay

History of the Earth ·

2018/04/03

Today we’re going back about 280 million years, to what is now Uruguay in South America. 280 million years ago puts us in the early part of the Permian Period. Gondwana, the huge southern continent, was in the process of colliding with North America and Eurasia to form the supercontinent of Pangaea. South America, Africa, Antarctica, India, and Australia had all been attached to each other in Gondwana for several hundred million years, and the extensive glaciers that occupied parts of all

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Episode 393 The Mountains of the Moon

History of the Earth ·

2018/03/27

Today we’re going to the Mountains of the Moon – but not those on the moon itself. We’re going to central Africa. There isn’t really a mountain range specifically named the Mountains of the Moon. The ancients, from Egyptians to Greeks, imagined or heard rumor of a mountain range in east-central Africa that was the source of the river Nile. In the 18th and 19th centuries, explorations of the upper Nile found the sources of the Blue Nile, White Nile, and Victoria Nile and identified the

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Episode 392 Ophiolites

History of the Earth ·

2018/03/20

Today’s episode focuses on one of those wonderful jargon words geologists love to use: Ophiolites. It’s not a contrived term like cactolith nor some really obscure mineral like pararammelsbergite. Ophiolites are actually really important to our understanding of the concept of plate tectonics and how the earth works dynamically. The word goes back to 1813 in the Alps, where Alexandre Brongniart coined the word for some scaly, greenish rocks. Ophiolite is a combination of the Greek words

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Episode 391 Valles Marineris

History of the Earth ·

2018/03/13

In today's episode we’re going to space. Specifically, Mars. You didn’t really think that earth science is really limited to the earth, did you? Our topic today will be the Valles Marineris. The Valles Marineris is a long series of canyons east of Olympus Mons, the largest mountain in the solar system. These canyons are about 4,000 km long, 200 km wide and up to 7 km (23,000 ft) deep. On terrestrial scales, the Valles Marineris is as long as the distance from New York to Los Angeles. That’s

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Episode 390 Mud Volcanoes

History of the Earth ·

2018/03/06

As the name implies, mud volcanoes are eruptions of mud – not molten rock as in igneous volcanoes. They’re found all around the world, amounting to about a thousand in total number known. The one thing they have in common is hot or at least warm water, so they occur in geothermal areas especially, but they also are found in the Arctic. They range in size from tiny, just a few meters across and high, to big things that can cover several square miles. In Azerbaijan some mud volcanoes reach

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Cretaceous and Cenozoic Vertebrates compilation

History of the Earth ·

2018/03/04

Smilodon and dire wolves (drawing by Robert Horsfall, 1913) Running time, 1 hour. File size, 69 megabytes. This is an assembly of the episodes in the original series from 2014 that are about Cretaceous and Cenozoic vertebrates. I’ve left the references to specific dates in the podcast so that you can, if you want, go to the specific blog post that has links and illustrations for that episode. They are all indexed on the right-hand side of the blog. Thanks for your interest and

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