The Great Ordovician Biodiversification Event, or 'GOBE', describes one of the most important increases in biodiversity in the history of life on earth. During a relatively short time span of some 25 million years, an explosion of new species, genera and families appeared. This increase in diversity was accompanied by an increase in ecosystem complexity. Plankton and suspension feeding organisms rapidly diversified and became important constituents of the food web. At the same time, large predators, such as the orthoconic nautiloids, evolved to exploit them. This biodiversity 'explosion' coincided with a dynamic period in earth's history during which continents were shifting, mountains were raised and massive volcanism occurred.

Joining us to try and untangle the causes and consequences of this complex and fascinating period is Prof. David Harper of Durham University, UK.