Privileged Planet: definite contents and oceans (Introduction)

by David Turell , Thursday, October 01, 2020, 05:24 (1515 days ago) @ David Turell

A new finding shows why the land and seas are not more mixed:

https://cosmosmagazine.com/earth/earth-sciences/how-planetary-forces-shape-earths-surfa...

"Airy was aware the shape of the Earth is very similar to a spinning fluid ball, distorted by the forces of rotation so that it bulges slightly at the equator and flattens at the poles. He concluded the interior of the Earth must be fluid-like.

"His measurements of the force of gravity in mine shafts showed the deep interior of the Earth must be much denser than the shallow parts.

"Airy then made an extraordinary leap of scientific thinking. He proposed that the outer part of the Earth, which he called the crust, must be floating on underlying “fluid”.

"An analogy might be an iceberg floating in water — to rise above the surface, the iceberg must have deep icy roots.

"Applying the same principle to the Earth, Airy proposed the Earth’s crust also had iceberg-like roots, and the higher the surface elevation, the deeper these roots must be, creating thicker crust.

"The continents define large continuous areas of land separated by oceans. The Earth’s crust is much thicker beneath the continents compared to the oceans. Simon Lamb, Author provided
Airy’s idea provided a fundamental explanation for continents and oceans. They were regions of thick and thin crust respectively. High mountain ranges, such as the Himalaya or Andes, were underlain by even thicker crust.

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"We found a surprising result – there seems to be little relation between the average elevations of the continents and the thickness of the underlying crust, except that the crust is much thicker than beneath the oceans. Most of the land area is within a few hundred metres of sea level, yet the thickness of the crust varies by more than 20km.

"So why don’t we see the differences in crustal thickness below a continent reflected in its shape above? Our research shows the underlying thick tectonic plate is acting as an anchor, keeping the elevations relatively low even though the buoyant crust wants to rise higher.

"We used measurements of the thickness of the tectonic plates, recently determined from the speed of seismic waves. The base of the continental plates reaches up to 250km deep, but most is between 100km and 200km deep.

"We also worked out the densities of the different layers from variations in the strength of gravity. It was clear that the dense roots of the plates were capable of pulling down the surface of the Earth in exactly the way needed to explain the actual elevations.

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"But why is there so much land close to sea level? The answer is erosion. Over geological time, major rivers wear away the landscape, carrying rock fragments to the sea. In this way, rivers will always reduce the continents to an elevation close to sea level."

Comment: A rocky planet with an iron-nickel core with floating crust arranged as designed is also a perfect place for life to thrive. Sounds designed to me. Thick under the continents and thin under the oceans.