This week in the Planet Earth Podcast - how the Romans recycled glass, dinosaur colour, and what Europe's gravity mission tells us about ocean currents. Did you know that the height of the world's oceans can vary by as much as 200 metres? These huge differences depend almost entirely on very slight changes in gravity across the world. Sue Nelson goes to the National Oceanography Centre in Southampton to find out more. We also hear that even the Romans recycled glass. But were they being green, or did they have other reasons? Richard Hollingham goes to Norwich to meet the archaeologists with the answer. Finally, what colour do you think dinosaurs were? Until now artists have been free to paint them whatever colour they felt like. But not anymore – scientists now have a way of figuring out what colour they were. Richard goes to Bristol University to get the low-down from one of the scientists at the forefront of this research.