Lurking at the bottom of every puddle and pond are tiny life forms called diatoms. Looking more like space ships than cells, the 20,000 species of diatom are now known to take more carbon dioxide out of the atmosphere than all the world's rainforests. Quentin Cooper talks to Professor David Mann from the Royal Botanical Gardens in Edinburgh about a life spent hunting these creatures, and hears how the glass-like cell walls of diatoms can provide a window on climate conditions millions Of years ago. Producer Marnie Chesterton