Rock composition and measuring the seismic waves provide knowledge for the scientists to study the interior of the earth.
Explanation:
When the crust gets distributed it is easy to study the layers of the different materials that got settled and compacted in the earth. Patterns that are formed in the rocks provides to be a good source to know about the earth's crust. rock cores are cylindrical sections which are cut and removed from the earth crust for research purposes.
It is impossible to drill to the center of the earth and so scientists rely on seismic waves and the speed of the seismic waves depends on the material on which it is passing through. The toughness and stiffness obstruct the speed of the waves which is a means for the scientists to undertake research on the substance which hampered the speed of the seismic waves. P-waves, or pressure waves, which go through both liquids and solids, and S-waves, or shear waves which go through solids but not liquids. This provides the best data to undertake research regarding the earth' crust by the scientists.
It would be the year "1991" that the Soviet Union officially "dissolved"--although it should be noted that the USSR was showing signs of dissolving long before this.
The answer is 2. Through their research and development, scientists have invented practical items such as cordless tools, memory foam in mattresses, and scratch-resistant glasses.
