Question

When was the Mohorovicic Discontinuity discovered?
a. 1909
b. 1908
c. 1910
d. 1920

Answer 1

Hint:
The Mohorovičić discontinuity was discovered by Andrija Mohorovičić. He observed that seismograms from shallow-focus earthquakes.


Complete solution:
The answer is option A, 1909. Mohorovicic Discontinuity is usually referred to as the Moho discontinuity, is the boundary between the Earth’s mantle and crust. It is defined by the distinct change in velocity of seismological waves as they pass through changing rock densities. The Moho lies almost entirely within the lithosphere. The Moho is 5 to 10 kilometres below the ocean floor, and 20 to 90 kilometres beneath typical continental crusts. The discontinuity separates both the oceanic and continental crust from the mantle that lies underneath. It is the transition in composition between the Earth's rocky outer crust and the more plastic mantle.

Croatian seismologist Andrija Mohorovičić is attributed with discovering and defining the Mohorovicic Discontinuity.

Andrija saw that waves that are caused by earthquakes travel at velocities proportional to the density of the material that carries them. As a result of this, he came up with a theory that the second set of waves could be caused by a sharp transition in density in the crust, that accounts for such a change in wave velocity. Using this velocity data from the earthquake, he calculated the depth of the Moho to be approx 54 km, which was later supported by future seismological studies.


Hence, the correct answer is option A.

Note:
 Moho discontinuity has played a large role in the Geological study and earth science. By observing its refractive nature and the way it affects the speed of P-waves, scientists were able to theorize about the earth's composition.