Briefly explain the indirect sources of information of the interior of the earth other than those of seismic activity.
Apart from seismic activity, the other indirect sources of information about the interior of the earth include:
Analysis of properties of matter: Through mining activity, it is known that temperature, pressure, and density increase with depth. Scientists have estimated values of these characteristics at different depths by knowing the total thickness of the earth.
Meteors: The material and structure observed in meteors are similar to that of the earth. They are solid bodies developed out of materials same as, or similar to, our planet, providing information about the interior.
Gravitation: The gravity values differ according to the mass of material. Gravity anomalies (difference between observed and expected values) give information about the distribution of mass in the crust.
Magnetic surveys: These provide information about the distribution of magnetic materials in the crustal portion.
Explanation
The question specifically asks for indirect sources OTHER than seismic activity. The textbook context clearly lists four other indirect sources: (1) Analysis of properties of matter through mining activity showing increase in temperature, pressure and density with depth; (2) Meteors which have similar material and structure to Earth; (3) Gravitation and gravity anomalies indicating mass distribution; and (4) Magnetic surveys revealing distribution of magnetic materials in the crust.