Mohorovicic Discontinuity, nicknamed "Moho," is the area where the earth's crust meets the earth's mantle. Moho is named after Andrija Mohorovicic (1857-1936), a Croatian meteorologist and seismologist who was fascinated with the faults and movements in the earth's infrastructure which result in earthquakes. The discovery of the Moho was most important because it helped scientists delimit the crust, and recognize a second layer, or mantle, inside the earth. It also helped them determine more accurately where this second layer was located in relation to the earth's crust. In the early 1900s, scientists were almost certain that the Earth, like an onion, was made up of many layers, but they did not know exactly where the layers started and ended.
Using records from a number of Yugoslavian earthquakes, Mohorovicic recognized that the same set of seismic waves appeared twice on a single earthquake record. Because the second set of waves exactly paralleled the first set, Mohorovicic concluded that the first set had traveled at a faster rate through a denser layer of rock deep inside the Earth. The second set had traveled at a slower rate, and a shorter distance, closer to the surface. This allowed Mohorovicic to interpret the thickness of the crust. He did this by gauging the time between the arrival of the two wave sets, which helped him determine how far this layer resided from the earth's surface. He also noticed from these experiments that the waves traveled at different speeds depending on the density of the material inside the earth. This information helped scientists discover the different types of rocks in areas where drilling was impossible. For example, the lowest level of the crust is composed of basaltic rock, the material that rests next to the mantle.
After the Moho was discovered, seismologists investigated its depth at a variety of locations, including the deep ocean basins. From this research, we know that the thickness of the crust is highly variable. It averages about three to six mi (five to 10 km) in the ocean basins, whereas below the continents it averages 20 mi (35 km). However, it is as much as 55 mi (90 km) thick beneath some mountain ranges.
Ever since the existence of the mantle became certain, scientists have wanted to probe into the physical nature of the earth's inner layer. And because the Moho is located so much closer to the surface beneath the ocean, there were plans in the late 1950s to drill into the Moho from floating platforms out at sea. But after a number of test drillings, the program experienced a drop in funding so "Project Mohole" was abandoned in the mid-1960s.
This is the complete article, containing 440 words
(approx. 1 page at 300 words per page).
