Professor Rachel Mills is a marine geochemist who studies the sea floor and hydrothermal vents, where water erupts from the earth's crust at 360 degrees. The thick plumes emit many metals such as copper, gold, iron and rare earth minerals that are deposited on the sea bed. Rachel's career has taken her all over the world and 4km deep under the ocean in small submersibles. These journeys are exciting and terrifying as samples are taken to understand how the metals travel many thousands of miles. The metals are involved in creating nutrients that supply the ocean's food chain and control carbon uptake. There is also a lot of interest in mining the valuable deposits but can this be done without upsetting the ocean's eco-system?