Exhibition Earth

 

This is a cross section of the earth. The Earth is made up of three main shells: the very thin, brittle crust, the mantle, and the core; the mantle and core are each divided into two parts.

Henk Caspers/Naturalis Biodiversity Center / CC BY-SA Detail

The outer rigid cool layers are called the lithosphere. This is composed of the crust and the uppermost mantle. The thickness of the lithosphere varies from around 1.6 km (at the mid-ocean ridges) to approximately 130 km. The outer brittle shell of the lithosphere is the crust. The crust is primarily made of granite and basalt while the uppermost mantle beneath is made of peridotite.
Below the lithosphere lies the asthenosphere. The asthenosphere is the least rigid portion of the mantle. The temperature is normally between 1,400 degrees Celsius and 3,000 degrees Celsius.

 

The Crust

In general, then, the crust has two types, oceanic crust, and continental crust.

Oceanic Crust

Oceanic crust covers about 60 per cent of the Earth's surface. Oceanic crust is thin and young, no more than about 20 km thick and never older than about 180 million years. It is primarily made of basalt.

Henk Caspers/Naturalis Biodiversity Center / CC BY-SA Detail

Continental Crust

Continental crust is thick and old,on average about 50 km thick and about 2 billion years old, and it covers about 40 per cent of the planet. It is primarily made of granite.

Upon this mass balance one litre of basalt is measured against one litre of granite. It is clear that the basalt is the densest. (Keep that in mind.)

Plate tectonics

The lithosphere is broken into pieces called tectonic plates. They fit around the globe like big puzzle pieces. However, unlike puzzle pieces, they are constantly moving and changing. Now what is the cause of that? The asthenosphere is made of a highly viscous, solid-ductile material somewhat comparable with the glass at the blowpipe of a glassblower, but under a much higher pressure. As a soft, easily deformable layer, the asthenosphere is susceptible to slow convection. This convection is caused by pockets of increased heat from the decay of radioactive elements. [Imagine the blobs of oil in a hot lava lamp??] This convection makes the plates drifting. Because of all this drifting, things are happening at the boundaries. What kind of things can happen at the boundaries of the plates? This is shown on the map below.
Plate tectonics
Henk Caspers/Naturalis Biodiversity Center / CC BY-SA Detail

From right to left:

  • South-America: the sea floor collides with the continent. As the sea floor is heavier, it subducts. Effects: eart quakes and forming of mountains and volcano’s.
  • The Pacific: Two sea floors collide. Effects: subduction, forming of deep sea through, forming of sea mounts and volcano’s.
  • Himalaya: Two continents collide.
  • East Africa: East African Rift System. Africa is falling apart. Effect: forming of lava lakes.
  • Atlantic: mid Atlantic ridge. Plates drift apart. Effect: sea floor spreading.

    • Now we return to the Nature Theatre.

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