What can the Earth tell us about itself?

Dr Chris Smith and the Naked Scientist team present the latest science news, analysis and breakthroughs. In today’s programme we look at how taking a daily brisk walk could take 25% off your mortality rate. The northern - and southern - lights and why they’ve been so pronounced of late? And have scientists discovered the world’s first Roman sex toy?Plus we look at the science of tectonics and ask, what can the Earth tell us about itself?