Iain travels to surfers' paradise Hawaii to learn more about oceans, explaining the difference between waves, tides and currents. In the Amazon, he rides the world's longest tidal bore. In the beginning, there were no oceans: they are thought to have gradually formed from volcano steam and melted comet ice. Change continues today: a new sea is forming in Ethiopia, which will separate East Africa from the mainland, and the Mediterranean is drying up.