Which one of the following is found in the innermost part of the Earth?
- (a)Conrad discontinuity
- (b)Moho discontinuity
- (c)Guttenberg discontinuity
- (d)Lehmann discontinuity
Correct — D, Lehmann discontinuity. Going inward, the seismic discontinuities are the Conrad (within the crust), the Mohorovicic/Moho (crust-mantle), the Gutenberg (mantle-outer core) and finally the Lehmann (outer core-inner core). The Lehmann discontinuity therefore lies deepest, in the innermost part of the Earth.
- (a)Conrad discontinuity — The Conrad discontinuity is within the continental crust (between the upper 'sial' and lower 'sima') — very shallow, not the innermost.
- (b)Moho discontinuity — The Mohorovicic (Moho) discontinuity separates the crust from the mantle — near the surface compared with the core.
- (c)Guttenberg discontinuity — The Gutenberg discontinuity separates the mantle from the outer core; it is deep, but the Lehmann (outer core-inner core) lies deeper still.
The Earth's layered interior is revealed by sudden changes in seismic-wave speed at boundaries called discontinuities. From the surface downward: Conrad (intra-crust), Moho (crust-mantle), Gutenberg (mantle-outer core, at about 2900 km), and Lehmann (outer core-inner core, at about 5150 km) — the deepest, marking the solid inner core.
Order the four discontinuities by depth. 'Innermost' means deepest, which is the Lehmann discontinuity at the outer-core/inner-core boundary; the others lie progressively closer to the surface.
- Conrad: within the crust (upper/lower crust).
- Moho: crust-mantle boundary.
- Gutenberg: mantle-outer core boundary (~2900 km).
- Lehmann: outer core-inner core boundary (~5150 km) — the innermost.
- Confusing the Gutenberg (mantle-outer core) with the deeper Lehmann (outer-inner core).
- Placing the Moho or Conrad deep — they are near the surface.
Asked as ordering the discontinuities by depth, or which lies innermost/at a given boundary.
No directly related past PYQ was found.
- practice — not a real PYQ
The boundary between the crust and the mantle is the
- (a)Conrad discontinuity
- (b)Moho discontinuity
- (c)Gutenberg discontinuity
- (d)Lehmann discontinuity
Answer(b) Moho discontinuity.
- practice — not a real PYQ
The Gutenberg discontinuity separates the
- (a)upper and lower crust
- (b)crust and mantle
- (c)mantle and outer core
- (d)outer and inner core
Answer(c) mantle and outer core.