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Geography

Layers of earth

The structure of Earth can be defined in two ways: by mechanical properties such as rheology, or chemically.

Mechanically, it can be divided into

  1. lithosphere,
  2. asthenosphere,
  3. mesospheric mantle,
  4. outer core, and
  5. inner core.

 

Chemically, it can be divided into

  1. crust,
  2. upper mantle,
  3. lower mantle,
  4. outer core, and
  5. inner core.

 

Discontinuities in earth structure:

  1. Connard discontinuity

            Zone that separates the Earth’s upper crust from the lower crust.

 

  1. Mohorovicic discontinuity.

            Zone that separates the Earth’s crust from the asthenosphere.

 

  1. Repetti discontinuity

           Zone that separates the upper mantle from the lower mantle.

 

  1. Gutenberg discontinuity

           Zone separating the lower mantle from the core; it is located at a depth of about 1,800 mi.

 

  1. Lehman Discontinuity

          Zone that separates the Earth's outer core from the Inner core.

 

It appears beneath continents, but not usually beneath oceans.

Several explanations have been proposed; a lower limit to the pliable asthenosphere, a phase transition, and most plausibly, depth-variation in the shear wave anisotropy.