In this latest watery-themed Planet Earth Podcast, Richard Hollingham hears how the underwater world isn't the soundless place you might imagine. From chirping, gurgling and snapping sounds from busy coral reefs to clicking sperm whales, scientists are finding that all sorts of marine life use sounds to find a suitable home, to find a mate, to avoid being eaten or to communicate. First up, we hear from a marine biologist from the University of Bristol who explains how manmade noise might not affect just whales and dolphins, but also much smaller creatures that live in and around coral reefs. Later, Richard meets a British Antarctic Survey scientist to find out how fossils of tiny marine creatures called bryozoans give us clues about when the West Antarctic Ice Sheet last collapsed. We also hear the strange clicking sounds sperm whales use to communicate with each other, and find out how very far leatherback turtles can swim.