There were no initiatives in the German-speaking regions to develop a reasonable geological theory on the foundation of these physical models that would have been applicable to larger, enigmatic structures such as the Ries Basin. In order to understand the problem, it is necessary to stray a bit into physics: small meteorites are effectively braked by friction within the atmosphere. The mechanism of explosion has been described in the English literature since the turn of the twentieth century and was initially proposed and calculated in an approximate manner for lunar craters, where the physics is simpler because the Moon lacks an atmosphere. In Europe, the physical modelling of impact structures as described above was done in the 1930s by two authors, the German mineralogist Fritz Heide and the astrophysicist Ernst Julius öpik. öpik was well aware that a meteorite impact theory would influence the view of the lunar craters as well as of Meteor Crater in Arizona.