MAJOR DISCONTINUITIES IN THE EARTH

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         Mehnat Aapki, Guidance Humari

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MAJOR DISCONTINUITIES IN THE EARTH

1. Conrad Discontinuity

The Conrad Discontinuity is the boundary separating the upper crust from the lower crust, mainly beneath continental regions. It lies at an average depth of 15–20 km and is generally absent beneath oceanic crust. The upper crust consists mainly of granitic rocks (Sial), while the lower crust is composed of basaltic rocks (Sima). This discontinuity is identified through changes in seismic wave velocities. It represents a change in rock composition rather than a sharp physical boundary. Although less distinct than the Moho, the Conrad Discontinuity helps geologists understand the internal structure, composition, and evolution of the continental crust.

2. Mohorovičić (Moho) Discontinuity

The Mohorovičić Discontinuity, commonly called the Moho, is the boundary between the Earth's crust and mantle. It was discovered in 1909 by Croatian seismologist Andrija Mohorovičić after observing sudden increases in seismic wave velocities. The Moho lies about 5–10 km beneath ocean floors and 30–70 km beneath continents, being deepest under mountain ranges. Above the Moho lies the lighter crust, while below it begins the denser mantle rich in silicate minerals. The Moho is one of Earth's most important geological boundaries and provides valuable information about crustal thickness, plate tectonics, and Earth's internal structure.

3. Repetti Discontinuity