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 answer
Explanation
The correct answer is D, Lehmann discontinuity. It separates the liquid outer core from the solid inner core at a depth of about 5,150 km, making it the deepest of the four boundaries.
The Earth’s layers are identified from the way seismic waves change speed and direction at certain depths. Danish seismologist Inge Lehmann found in 1936 that faint P-waves were reflected from a boundary inside the core, which showed that the inner core is solid. Going outward from it come the Gutenberg discontinuity between core and mantle at about 2,900 km, the Repetti discontinuity between the upper and lower mantle, the Mohorovicic (Moho) discontinuity at the base of the crust, and the Conrad discontinuity inside the crust.
A is wrong because the Conrad discontinuity lies within the continental crust, between its upper (sial) and lower (sima) parts. B is wrong because the Moho marks the base of the crust, only about 5–70 km deep. C is wrong because the Gutenberg discontinuity separates the mantle from the outer core at about 2,900 km, above the Lehmann boundary.
Exam tip: from top down: Conrad, Moho, Repetti, Gutenberg, Lehmann.
Practice Questions
View allWhich one of the following lakes in India has a large quantity of a substance found in the Moon?
- A.Lonar Lake, Maharashtra
- B.Pangong Lake, Ladakh
- C.Chilika Lake, Odisha.
- D.Loktak Lake, Manipur
Show answer
Lonar was formed by a meteorite impact, and its rocks contain maskelynite, a natural glass that forms only under such high-velocity impacts and is also found in lunar rocks.
Read the full explanation →What does BW stand for as per the Koeppen climate classification?
- A.Steppe climate
- B.Desert climate
- C.Tundra climate
- D.Mesothermal climate
Show answer
In Koeppen's scheme B marks dry climates, and the letter W, from the German Wüste meaning desert, marks the driest of them.
Read the full explanation →Extrusive volcanoes are not found in which one of the following mountains?
- A.Alaska
- B.Rocky
- C.Andes
- D.Himalayas
Show answer
The Himalayas were formed by the collision of two continental plates, the Indian and the Eurasian, and such a collision does not produce volcanoes.
Read the full explanation →Indus river basin is extended up to
- A.Ladakh, Jammu and Kashmir, Himachal Pradesh, Punjab
- B.Ladakh, Jammu and Kashmir, Punjab, Haryana
- C.Ladakh, Jammu and Kashmir, Punjab, Haryana, Rajasthan
- D.Ladakh, Jammu and Kashmir, Himachal Pradesh, Punjab, Haryana, Rajasthan
Show answer
The Indian part of the Indus basin covers all six, along with Chandigarh. The Indus rises near Lake Mansarovar in Tibet and enters India in Ladakh.
Read the full explanation →Which peninsular river has a tributary named Kabini?
- A.Godavari
- B.Krishna
- C.Mahanadi
- D.Kaveri
Show answer
The Kabini rises in the Wayanad district of Kerala and flows into Karnataka, where it joins the Kaveri near Tirumakudalu Narasipura.
Read the full explanation →