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Some of the direct sources are:-
• Mining: It is a process by which commercially variable valuable mineral resources are extracted from Earth’s surface which includes precious stones, rocks and solid fuels.
• Drilling: Scientists world over are working on two major projects such as “Deep Ocean Drilling Projects” and “Integrated Ocean Drilling Project”. The deepest drill at Kola, in Arctic Ocean, has so far reached a depth of 12 km.
• Volcanic Eruptions: When molten material is thrown onto the surfaced earth during volcanic eruption it becomes available for analysis