Sediment samples taken from the ocean floor can be used to measure the grain size, limestone or silica content, trace element and nutrient levels. These are basic measurements of the seabed which are just as important as if describing the characteristics of soils on land. As well, much of our knowledge about the animals that live in and on the seabed have come through looking at the rocks and mud collected by sediment grabs. Worms and other sediment-feeding animals make their homes in the seabed and a grab is often the most simple device used to collect them.