Which one of the following ‘discontinuities’ separates the Earth’s crust from the mantle?

The Earth's interior is divided into distinct layers separated by seismic discontinuities where wave velocities change abruptly due to physical or chemical shifts [2]. The Mohorovicic Discontinuity, commonly known as the 'Moho', is the boundary that separates the Earth's crust from the underlying mantle [1][2]. Discovered by Andrija Mohorovicic in 1909, it marks a transition from silica-rich crustal rocks to denser, ultramafic mantle rocks, resulting in a sharp increase in P-wave velocity. In contrast, the Conrad discontinuity separates the upper and lower crust [2], while the Repetti discontinuity divides the upper mantle from the lower mantle [2]. The Gutenberg discontinuity is located much deeper, at approximately 2,900 km, serving as the boundary between the mantle and the liquid outer core [2].

Sources

1. [2] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Seismic Discontinuities > p. 56
2. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > The Mohorovicic (Moho) Discontinuity > p. 53