Gondwana Cratons

A Craton is an ancient piece of earth’s continental crust, one that has been stable for billions of years.

The Earth naturally contains elements that give off heat, such as radioactive potassium, thorium, and uranium. When the mantle melts, those elements move into the melt, extracting them from the mantle and moving them upward. Once those elements are concentrated in the crust, the heat can rapidly escape out into space. Once that heat is removed, the crust can become cold and stable, hard to deform.

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Cirrus clouds off the Chilean coast

Several layers of clouds are visible at different altitudes in this image taken by the MODIS instrument on NASA’s AQUA satellite, though the amazing wispy ones taking centre stage from top right to bottom left are high altitude cirrus clouds, made of falling ice crystals. They form when turbulence in the fast moving jet stream sucks up moister air from below, whose water swiftly freezes into minute ice particles. These crystals then spread out with the prevailing winds (in this case some 160kph at 13km altitude), forming some lovely shapes from whichever perspective they are viewed. Sooner or later gravity reasserts its sway, and they gently start to fall back down towards Terra Firma.

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The Edge of the World

Cape Roca in Portugal’s Sintra Cascais Natural Park is the westernmost point of mainland Europe. In fact, up until the late 14th century, there were people who thought it was the edge of the world.

The cape has sandy beaches and magnificent cliffs that have been sculpted by waves and continuous strong winds. Many of the cliffs are over 100 meters (330 feet) in height. They are a mix of granite, sedimentary (mostly limestone and marlstone), and metamorphic rock formed where the granite and sedimentary have mixed.

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Photo Credit: Husondhttp://bit.ly/1H75tr4
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The view from above

When bimbling through a country by whatever means of transport, from a high speed TGV train to good old shanks mare, one gets immersed in the local details, and we often lose sight of the bigger picture… until a photo of a wider view comes along to remind you that it exists. I’ve criss-crossed my native country dozens of times, noting some of the features of the land as I pass through, but am impressed with the succinctness with which this winter image evokes my knowledge.

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Plate tectonics

It was first truly understood that the plates of the Earth move across the planet’s surface in the 1960s. The evidence at the time was tectonic –faults and mountain ranges on the ocean floor, and magnetic – stripes parallel to the ocean ridges formed in the presence of a magnetic field that occasionally flips which direction it points.

Today, we have new ways of measuring the motion of the Earth’s surface. Lasers can measure the distance between two points with impressive accuracy and radar techniques can see how rock positions change with time. Beyond those though is a tool many of us use every day just to get around: the Global Positioning System.

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A deeper look

Lurking beneath all the more recent layers of rocks that drape our continents are their roots, the oldest of which are the remnants of cratons, the first nuclei of the light buoyant surface rocks that float atop the underlying mantle. When they pop into visibility at the surface, the most amazing patterns reveal themselves. These rocks have been repeatedly heated, melted and compressed as the continents moved back and forth, colliding and separating into supercontinents in their Wilson cycles.

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Cliffs in Svalbard’s Isfjorden

This cliff is one of many in Isfjorden in the Svalbard archipelago far to the north of Norway.

The islands are a small sliver of land sitting in a far corner of the Eurasian Plate. They have been gradually pushed up as a consequence of the motion between Greenland, North America, and Europe.

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The Grand Canyon Metamorphic Suite

Yesterday I started at the very bottom of the Grand Canyon by highlighting the Elves Canyon Gneiss, the single oldest piece of rock exposed in the canyon.

Surrounding the Elves Canyon Gneiss is a much larger area of metamorphic rocks, the Grand Canyon Metamorphic suite. This picture captures two of those units; the Granite Gorge Granites (also called the Zoroaster granite) and the Vishnu Schist.

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