Erle Ellis, associate professor of geography and environmental systems was taking a walk down the beach when he found a smooth object. Thinking it was some relic of years of ocean polishing he put it in his pocket only to discover a trash heap a short distance away. Triggered by his accidental discovery, Ellis measured on a global scale how much of Earth has been changed by humans. Using satellite data, he concluded that at least two thirds of the land surface have already been modified for agriculture, cities, mining and other human purposes. The oceans have also become an …