Direct sources of information about the interior
Topic: Interior of the Earth: Earthquakes, Volcanoes and the Layered Earth · NCERT: Class 11, Ch 3 "Interior of the Earth"
Meaning
Direct sources are earth materials we can actually see, touch and test in a laboratory. They include surface rocks, rocks brought up from mines, rock samples from deep drilling, and magma thrown out by volcanoes. They are few and shallow. The deepest mines reach only 3-4 km, because it gets too hot to work below that. Volcanic magma can be tested, but we cannot tell how deep it came from. So direct sources tell us only about the outer skin of a planet whose radius is about 6,371 km.
Example
At Koyna in Maharashtra, the Ministry of Earth Sciences runs a Scientific Deep Drilling project to study earthquakes set off by the reservoir. Its pilot borehole is about 3 km deep. Outside India, South African gold mines go 3-4 km down, and ocean projects such as the Deep Ocean Drilling Project and the Integrated Ocean Drilling Project bring up rock cores from under the sea.
Don't confuse with
- Indirect sources of information about the interior: these are clues we read from outside, such as seismic waves, gravity and meteors. Volcanic material counts as a direct source, not an indirect one.
Related concepts
- Indirect sources of information about the interior
- Kola Superdeep Borehole
- Geothermal gradient
- Gravity anomaly