Last week's edition focused on the Burgess Shales, the Cambrian Explosion, and evolutionary matters in general. With a line-up that included Simon Conway Morris (one of the early experts in Edicarian fauna), this was an example of what public service broadcasting should be - an intelligent round-table debate that took three viewpoints and used them to expound on palaeo-climatology, modern evolutionary thought, the thesis of Steven Jay Gould's Wonderful Life, and on the scientific process - all in a half-hour slot.
In the Selkirk Mountains of British Columbia in Canada, there is an outcrop of limestone shot through with a seam of fine dark shale. A sudden mudslide into shallow water some 550 million years ago means that a startling array of wonderful organisms has been preserved within it. Wide eyed creatures with tentacles below and spines on their backs, things like flattened rolls of carpet with a set of teeth at one end, squids with big lobster-like arms. There are thousands of them and they seem to testify to a time when evolution took a leap and life on this planet suddenly went from being small, simple and fairly rare to being large, complex, numerous and dizzyingly diverse. It happened in the Cambrian Period and it's known as the Cambrian Explosion.MP3s of the show are available from the BBC for a limited time.