The correct option is 2 and 3 only.
Explanation
Understanding the interior of the Earth relies on both direct sources (such as deep ocean drilling and volcanic eruptions) and indirect sources (such as seismic waves, gravity anomalies, and magnetic fields). Volcanic eruptions bring material from deep within the Earth to the surface, offering tangible samples for analysis.
Statement-wise Analysis:
- Statement 1 is Incorrect. Volcanic eruptions are a primary direct source of information about the interior of the Earth. When molten material (magma) is ejected onto the surface, it becomes available for laboratory analysis, allowing scientists to study the chemical composition of the Earth's upper layers.
- Statement 2 is Correct. While volcanic eruptions provide samples of magma, it is scientifically difficult to ascertain the precise depth of the source of such magma. The magma rises through complex conduits, and pinpointing the exact depth of the magma chamber based solely on the erupted material is challenging.
- Statement 3 is Correct. The upper portion of the mantle is known as the asthenosphere. It is a weaker, plastic-like layer extending up to 400 km deep. This layer is the primary source of magma that reaches the surface during volcanic eruptions.
Key Takeaway:
Volcanic eruptions serve as a direct source of information regarding the Earth's interior. The magma analyzed from these eruptions primarily originates from the asthenosphere, located in the upper mantle.