Geology Reference
In-Depth Information
In 1909, Andrija Mohorovicˇic´, a Croatian seismologist, noticed that earthquake waves increased their
speed as they moved through the lower part of the earth's crust. He interpreted (correctly) that this
meant the lower portion of earth's lithosphere is made of a different and slightly more dense material
than the very outer crust. The line where the material in earth's lithosphere changes from the crustal
rock to the mantle rock (the asthenosphere) is named the
Moholine
or the
Mohorovicˇic´Discontinuity.
For decades scientists have attempted drilling deep into the earth, seeking to reach the Moho line
between the upper mantle and crust. In 2005 a team of scientists with the Integrated Ocean Drilling
Program (IODP) came close. The core they drilled near the mid-Atlantic ridge in the Atlantic Ocean
reached a depth of 1,416 meters (4,644 feet) into the oceanic crust. But the rocks they recovered appear
to be made of crustal rock materials rather than the mantle rocks they were seeking. The research-
ers concluded that they were close to crossing the Moho discontinuity boundary and plan to attempt
drilling a new hole.
Every inch closer to the Moho provides scientists with new information about the composition and
formation of the earth's crust and offers clues to earth's internal structure.
