Japan and Hugo Benioff of the United States. The study of global seismicity greatly advanced in the 1960s with the establishment of the Worldwide Standardized Seismograph Network (WWSSN) to monitor the compliance of the 1963 treaty banning above-ground testing of nuclear weapons. The much improved data from the WWSSN instruments allowed seismologists to map precisely the zones of earthquake concentration worldwide. Meanwhile, debates developed around the phenomenon of polar wander. Since the early debates of continental drift, scientists had discussed and used evidence that polar drift had occurred because continents seemed to have moved through different climatic zones during the past. Furthermore, paleomagnetic data had shown that the magnetic pole had also shifted during time. Reasoning in an opposite way, the continents might have shifted and rotated, while the pole remained relatively fixed. The first time the evidence of magnetic polar wander was used to support the movements of continents was in a paper by Keith Runcorn in 1956, and successive papers by him and his students Ted Irving (who was actually the first to be convinced of the fact that paleomagnetism supported continental drift) and Ken Creer. This was immediately followed by a symposium on continental drift in Tasmania in March 1956 organised by Prof. S. Warren Carey who had been one of the supporters and promotors of Continental Drift since the thirties During this symposium, some of the participants used the evidence in the theory of an expansion of the global crust, a theory which had been proposed by other workers decades earlier. In this hypothesis, the shifting of the continents is explained by a large increase in the size of Earth since its formation. However, although the theory still has supporters in science, this is generally regarded as unsatisfactory because there is no convincing mechanism to produce a significant expansion of Earth. Other work during the following years would soon show that the evidence was equally in support of continental drift on a globe with a stable radius. During the thirties up to the late fifties, works by Vening-Meinesz, Holmes, Umbgrove, and numerous others outlined concepts that were close or nearly identical to modern plate tectonics theory. In particular, the English geologist Arthur Holmes proposed in 1920 that plate junctions might lie beneath the sea, and in 1928 that convection currents within the mantle might be the driving force. Often, these contributions are forgotten because: At the