Death Wegener died in Greenland in November 1930 while returning from an expedition to bring food to a group of researchers camped in the middle of an icecap. He supplied the camp successfully, but there was not enough food at the camp for him to stay there. He and a colleague, Rasmus Villumsen, took dog sleds to travel to another camp – which they never reached. Villumsen buried Wegener's body with great care, a pair of skis marking the grave site. After burying Wegener, Villumsen resumed his journey to West camp, but he was never seen again. Six months later, on 12 May 1931, the grave was discovered halfway between and West camp. Expedition members built a pyramid-shaped mausoleum in the ice and snow, and Alfred Wegener's body was laid to rest in it. Wegener had been 50 years of age and a heavy smoker, and it was believed that he had died of heart failure brought on by overexertion. Villumsen was 23 when he died, and it is estimated that his body, and Wegener's diary, now lie under more than of accumulated ice and snow. Continental drift theory Alfred Wegener first thought of this idea by noticing that the different large landmasses of the Earth almost fit together like a jigsaw puzzle. The continental shelf of the Americas fits closely to Africa and Europe. Antarctica, Australia, India and Madagascar fit next to the tip of Southern Africa. But Wegener only published his idea after reading a paper in 1911 which criticised the prevalent hypothesis, that a bridge of land once connected Europe and America, on the grounds that this contradicts isostasy. Wegener's main interest was meteorology, and he wanted to join the Denmark-Greenland expedition scheduled for mid-1912. He presented his Continental Drift hypothesis on 6 January 1912. He analysed both sides of the Atlantic Ocean for rock type, geological structures and fossils. He noticed that there was a significant similarity between matching sides of the continents, especially in fossil plants. From 1912, Wegener publicly advocated the existence of "continental drift", arguing that all the continents were once joined together in a single landmass and had since drifted apart. He supposed that the mechanisms causing the drift might be the centrifugal force of the Earth's rotation ("") or the astronomical precession. Wegener also speculated about sea-floor spreading and the role of the mid-ocean ridges, stating that "the Mid-Atlantic Ridge ...