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Friday, August 20, 2021

Sea Floor Expansion Pushes Continents Apart

 

Ridge zone where sea floor spreads.


Only a small portion of the oceanic crust produced in the Atlantic is subducted. Most is rising and the rising rock appears to be slowly pushing the continents of North and South America further apart from Europe and Africa. The spreading distance between North America and Europe is caused by mantle convection. The Atlantic is expanding by a couple of inches a year. 

The North American and Eurasian Plates are moving away from each other along the line of the Mid- Atlantic Ridge. The Ridge extends into the South Atlantic Ocean between the South American and African Plates. The ocean ridge rises to between 1.24 and 1.86 miles above the ocean floor, and a rift valley at its crest marks the location where the two plates are moving apart.

The Mid Atlantic Ridge has developed as a consequence of the divergent motion between the Eurasian and North American, and African and South American Plates. As the mantle rises towards the surface below the ridge the pressure is lowered (decompression) and the hot rock starts to partially melt. This produces basaltic volcanoes when an eruption occurs above the surface. An example is Eyjafjallajökull in Iceland

As the plates move further apart new ocean lithosphere is formed at the ridge and the ocean basin gets wider. This process is known as “sea floor spreading” and results in a symmetrical alignment of the rocks of the ocean floor which get older with distance from the ridge crest.




Friday, August 6, 2021

Stone 58 Sediments Date to 1.6 Billion years

 

A 3-inch-long sample of the core from Stone 58 was used for detailed analyses. (Image credit: British Geological Survey)


A long-lost piece of Stonehenge that was taken by a man performing restoration work on the monument has been returned after 60 years, giving scientists a chance to peer inside a pillar of the iconic monument for the first time.

In 1958, Robert Phillips, a representative of the drilling company helping to restore Stonehenge, took the cylindrical core after it was drilled from one of Stonehenge's pillars — Stone 58. Later, when he emigrated to the United States, Phillips took the core with him. Because of Stonehenge's protected status, it's no longer possible to extract samples from the stones. But with the core's return in 2018, researchers had the opportunity to perform unprecedented geochemical analyses of a Stonehenge pillar, which they described in a new study.

They found that Stonehenge's towering standing stones, or sarsens, were made of rock containing sediments that formed when dinosaurs walked the Earth. Other grains in the rock date as far back as 1.6 billion years.

Read more here.