Seismology Group IIT Kharagpur Complex Continents • Age: 4200 Ma old. • Oldest material at their center flanked by younger materials: representing many events of mountain building, • Direct Observations limited to exposures at or near collision, rifting and plate convergence and subsidence. • Composition of the Lower Crust • Nature of the Moho and upper mantle • Strength of the Lithosphere • Mountain Building, support and destruction Matters of Current Debate