What is a core?

The gravity core is the most basic sampling device used to collect core samples from the seafloor, it penetrates less than 10 metres into the sediment

A core is a vertical cylinder or block of sediment, retrieved by forcing a metal tube, or a metal box, into the sediment, closing a lid at the bottom to trap the sediment inside, and then pulling it out again. This 'slice' will contain a section down through layers of sediment which have accumulated over time at that spot.