Part 2. Diatoms are a major group of algae found in waters all around the world. As photosynthetic phytoplankton, they are hugely important ‘primary producers’, integral to nearly every aquatic food chain. They are responsible for a large proportion of the world’s oxygen production, with estimates ranging between 20 and 50%. Diatoms are unicellular plants that produce their cell walls, termed frustules, out of silica. These intricate frustules are what we find preserved in the fossil record and they can contain an absolute wealth of information. In this interview, Prof. Anson Mackay, University College London, joins to discuss his work on the diatoms from Lake Baikal, Siberia. We learn why lakes are such special ecosystems and what diatoms can tell us about the world through studies of their palaeoproductivity over thousands of years.