Pulsation hypothesis
The pulsation hypothesis is a model of the evolution of the earth, which assumes a cyclical increase and decrease in the earth's radius . It emerged at the turn of the century from the contrast between theories of shrinkage and expansion and was represented by geologists John Joly and Arthur Holmes , among others .
While the older contraction theories primarily aimed to interpret mountain formation through the formation of folds in the shrinking earth's crust , other scientists (including Mantovani and later Pascual Jordan ) imagined the opposite, for example permanent or alternating expansion through thermal expansion or through changes in the gravitational constant . In order to be able to explain phenomena such as cracks in the lithosphere , Holmes postulated around 1930 - when Alfred Wegener's continental drift was increasingly accepted - a quasi-periodic expansion and contraction of the earth's body , in which the earth's circumference would remain almost unchanged in the long term. According to this hypothesis, a pulsating mechanism of heat flows in the earth's interior should also generate enough force to cause the continental plates to move on the subsurface of the earth's mantle .
From around 1960, all of these ideas led to the theory of plate tectonics , although the question of the causative forces still remains open.
- Sedimentology
Pulsation theories were also developed in sedimentology for phenomena where more or less regular repetitions of certain rock sequences occur. They were first analyzed by geologist W. Klüpfel in 1917. In the Variscan depths they are called small cycles or cyclothemes , while the term pulsation is used more for medium and large cycles (cycle theory ).
See also
Web links
Individual evidence
- ↑ Helmut Hölder : Brief history of geology and paleontology. A reader. Springer, Berlin et al. 1989, ISBN 3-540-50659-4 .
- ^ Hans Murawski , Wilhelm Meyer : Geological dictionary. 11th, revised and expanded edition. Elsevier - Spektrum Akademischer Verlag, Munich 2004, ISBN 3-8274-1445-8 .