They make up nearly a fifth of all life on the planet and live in some of the most extreme habitats on Earth and yet most people have never heard of the archaea. These microscopic organisms are found in the craters of volcanoes, in hot, sulphurous springs and even underthe ice sheets of Antarctica. Peter Evans investigates these most unusual life forms and talks to the scientists who think they may answer some fundamental scientific mysteries.
Could the archaea tell us what life on other planets might look like, or even uncoverthe causes of terrible and little-understood diseases? Producer Alexandra Feachem