What does the Moho line signify?

The Moho line, short for Mohorovičić discontinuity, signifies the boundary between the Earth's crust and the underlying mantle. This boundary is critical in understanding the Earth's internal structure. The Moho is named after the Croatian seismologist Andrija Mohorovičić, who discovered it in the early 20th century by analyzing seismic waves. It marks a transition where there is a significant change in composition and density between the crust, which is predominantly made up of lighter rocks like granite and basalt, and the mantle, which consists of heavier silicate minerals.

In terms of geophysical studies, the Moho is important for seismic investigations as it reflects changes in wave velocity. Seismic waves travel faster through the denser mantle than through the less dense crust, which is why identifying the Moho is essential in geological mapping and understanding tectonic processes. The incorrect options do not accurately describe the Moho's significance; for instance, the boundaries between tectonic plates, the depth of the ocean floor, and areas of seismic activity pertain to other geological concepts rather than directly relating to the crust-mantle boundary.