Scientists select a coral reef where they detect a clear and identifiable climatic signal. They take a boat to the area of study and then dive down to carefully drill and remove a core sample. They try to get the longest sample possible. Once the core sample is shipped back to the laboratory, scientists used x-rays to examine the growth bands. Each band, or layer of the coral skeleton, contains calcium carbonate. Isotopes and trace minerals in the calcium carbonate reveal data about the sea water at the time of formation. Scientists study the growth bands to determine the conditions under which the coral skeleton was created in each season of its history.