Sample drilling (or core sampling) is a technique that is used in mining when prospecting for minerals or other deposits. A core sample is a cylindrical piece of subsurface material that is gathered using equipment that has a special drill that brings it to the surface for testing. These samples are used to check the properties of underground rocks (such as whether it is porous or permeable), to investigate the composition or features of a particular area or to determine whether an area contains a particular mineral or other deposit (such as oil or gas).
Another reason to recover core samples is to identify layers of deposits which have been laid down in a sequence over time to infer various facts about what occurred during different time periods. This technique is used on the seabed to analyze mineral grains, microfossils and other deposits to draw conclusions about past oceanic events, It has also been used in ice deposits to determine the chemical composition of the atmosphere in the deep past.