P <peter@makholm.net> wrote:
> Kan du prøve at slå op under pladetektonik og se hvad der står
> der.
Du kan få en /introduktion/ fra mit leksikon, der imidlertid rummer
/meget mere/ om emnet:
plate tectonics
theory dealing with the dynamics of the Earth's outer shell, the
lithosphere. According to the theory, the lithosphere consists of about
a dozen large plates and several small ones. These plates move relative
to each other and interact at their boundaries, where they diverge,
converge, or slip relatively harmlessly past one another. Such
interactions are thought to be responsible for most of the seismic and
volcanic activity of the Earth, although earthquakes and volcanoes are
not wholly absent in plate interiors. While moving about, the plates
cause mountains to rise where they push together and continents to
fracture and oceans to form where they pull apart. The continents,
sitting passively on the backs of plates, drift with them and thereby
bring about continual changes in the Earth's geography.
The theory of plate tectonics, formulated during the late 1960s, rests
on a broad synthesis of geologic and geophysical data. It is now almost
universally accepted and has had a major impact on the development of
the Earth sciences. Its adoption represents a true scientific
revolution, analogous in its consequences to the Rutherford and Bohr
atomic models in physics or the discovery of the genetic code in
biology. Incorporating the much older idea of continental drift, the
theory of plate tectonics has made the study of the Earth more difficult
by doing away with the notion of fixed continents, but it has at the
same time provided the means of reconstructing the past geography of
continents and oceans. While its impact has, to a considerable degree,
run its course in marine geology and shows signs of reaching the limits
of usefulness in the study of mountain-building processes, its influence
on the scientific understanding of the Earth's history, of ancient
oceans and climates, and of the evolution of life is only beginning to
be felt.
For details on the specific effects of plate tectonics, see earthquake
and volcano. A detailed treatment of the various land and submarine
relief features associated with plate motion is provided in tectonic
landform and oceans.
Copyright © 1994-2002 Encyclopædia Britannica, Inc.
=======
Skal man tage udsagnet om at kontinenter sidder passivt på pladernes
ryg, så kan et kontinent ikke omfatte mere end én plade. Da kan hverken
Arabien eller Indien være en del af Eurasien ...
--
Cand.scient. Per Erik Rønne
Frederikssundsvej 308B, 3. tv.
DK-2700 Brønshøj
Tlf + fax 38 89 00 16, mobil 28 23 09 92