The structure of Earth can be defined in two ways: by mechanical properties such as rheology, or chemically.
Mechanically, it can be divided into
- lithosphere,
- asthenosphere,
- mesospheric mantle,
- outer core, and
- inner core.
Chemically, it can be divided into
- crust,
- upper mantle,
- lower mantle,
- outer core, and
- inner core.
Discontinuities in earth structure:
- Connard discontinuity
Zone that separates the Earth’s upper crust from the lower crust.
- Mohorovicic discontinuity.
Zone that separates the Earth’s crust from the asthenosphere.
- Repetti discontinuity
Zone that separates the upper mantle from the lower mantle.
- Gutenberg discontinuity
Zone separating the lower mantle from the core; it is located at a depth of about 1,800 mi.
- 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.