These deep-sea sediment cores were drilled from beneath the seafloor, and hold information about millions of years of ocean and atmospheric chemistry. As dirt, dead organisms, and other particles settle to the seafloor, they build up in layers, with the deepest layers containing the oldest material and the surface holding the newest. Like tree rings, each layer in the core records conditions about the atmosphere—oxygen isotopes, methane concentrations, dust content, even volcanic eruptions—in the sediment and dead microorganisms such as foraminifera. This core comes from off the Southeast coast of Britain, an area which was once dry land. Note the change in color and materials at different depths.