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30A

The Thickness of the Earth’s Crust (Lithosphere)

 

We can begin to understand the evolution of the Earth’s crust by studying its thickness and the overlying sedimentary geology. The crust varies in thickness from 7 km to 70 km.

 

Measurements of crust thickness were first taken by a Croatian seismologist, named Mohorovicic in 1909. He was the first to realise there was a change in the nature of the crust below a certain level. Seismic waves were seen to increase velocity at this point which is now commonly referred to as the Mohorovicic Discontinuity or, abbreviated, ‘the Moho’.

 

Since that time measurements have been made of the crust thickness in many parts of the World. Using these measurements, the United States Geological Survey (USGS) have published a map of the World which shows the crustal thickness as contours:-

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Image USGS

 

I have adapted these contour lines onto a map of each continent - to illustrate the sequence of stretching that has taken place over the last billion years as the planet has grown in size. I will classify the various thick-nesses of crust taking references from the first contour map, Europe.

 

Europe

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

THE EVOLUTION OF THE EARTH’S CRUST

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