The correct option is 1 only
Explanation
The study of the Earth's interior is primarily based on indirect sources because direct observation is limited to a negligible depth (mining and drilling). Seismic activity, which involves the propagation of earthquake waves (P-waves and S-waves), serves as the most significant indirect method for understanding the Earth's internal structure.
Statement-wise Analysis
- Statement 1 is Correct: Seismic activity is considered one of the most important sources of information regarding the Earth's interior. By analyzing the velocity, reflection, and refraction of seismic waves as they travel through the Earth, scientists can infer the density, temperature, and state of matter (solid or liquid) of different layers.
- Statement 2 is Incorrect: Seismic waves provide critical information about the layered interior. The change in direction and velocity of waves as they pass through materials of different densities helps identify boundaries between the crust, mantle, and core. For instance, the "shadow zones" of P and S waves helped confirm that the outer core is liquid.
- Statement 3 is Incorrect: All natural earthquakes take place in the lithosphere. The lithosphere refers to the solid, brittle portion of the Earth, which includes the crust and the uppermost part of the mantle. It extends up to a depth of approximately 200 km. Earthquakes do not occur in the inner core due to the extreme pressure and temperature, which prevent the brittle fracture of rocks required to generate seismic shocks.
Key Takeaway
Seismic waves are the primary tool for mapping the Earth's layered interior (Crust, Mantle, Core). Natural earthquakes are confined to the lithosphere, where rocks are brittle enough to fracture and release energy.