Milestones in precise Earth observation and their impact

In 1922, the founding year of the German Geophysical Society (Deutsche Geophysikalische Gesellschaft e.V., DGG), the idea of ’continental drift’, advocated by Alfred Wegener since 1912, was still highly controversial. Nowadays, we are used to observe earthquakes and plate tectonics in real time by using recordings of the global seismological networks and observations made with the Global Navigation Satellite System (GNSS). In 100 years of its existence, the DGG has seen a tremendous development of our understanding of Earth’s internal structure and dynamics. This development was only made possible by ever more precise instrumental techniques to measure the globe’s physical properties and changes. Several formerly well established ideas have been questioned and were finally discarded due to the undeniable evidence of new observations. Much has been written about the history and development of geophysics. It would be presumptuous to try to add relevant new aspects on these few pages and we will not even try to make a complete reference to review literature. Instead we assembled our selective (and likely subjective) timeline in Figure 1, which we complement with anecdotes on certain events. In our small contribution we would like to share with the reader the fascination we feel as we look back on this history of geophysical observations.