Q. Which of the following is an example of direct source to study interior of the earth?
Answer: Volcanic Eruption
Notes: Temperature increases when we go deep into the earth. Therefore scientist depends on some sources to study interior of the earth.  Based on the nature of source they are divided into two types: Direct sources- Surface rocks, volcanic eruption forms etc. Indirect sources- Magnetic field, gravitation, seismic activity, meteors etc.