Eduard Suess had lined up the mountains on
different continents
by linking their fossils, but he claimed that land-bridges
connecting the continents must have sunken below the ocean,
which Alfred Wegener realized would not work because it
contradicted
the geological buoyancy of the continental masses. Wegener
further
realized that the continents had been slowly drifting about
the globe,
and that the mid-ocean ridges were being filled with new
seafloor
as each side spread apart. Nevertheless, Wegener did not
understand
the cause of continental drift. That waited for the theory
of plate tectonics.
Pangaea
Pangaea, which Wegener called Urkontinent,
existed from three hundred million years ago
when all the continents and subcontinents
were jammed together.
Two hundred million years ago, Panaea began
to split into Gondwana to the south
and Laurasia to the north.
Gondwana included Antarctica, Africa,
Madagascar, Australia, Arabia, India,
and South America
and began to break up in the early Jurassic,
about one hundred eighty-four million years ago.
Laurasia included Europe without the Balkans,
Siberia, Asia without India, Greenland,
and North America
and began to break up at the end of the Paleocene,
about fifty-five million years ago.
Today, India is ramming into Asia
lifting up the Himalayas
and the Great Rift is separating Africa
from its horn.
My drift
If you get my drift,
my slowly imperceptible
displacement, then
you might begin
to correlate other facts
in reconstructing my past.
Not everything has been
lost, I could say, none
of the important things,
but even trivial fossils
have become important
enough to cherish.
Alfred Wegener thought that continents drifted because of
centrifugal forces; today the picture is more complicated,
involving convection in the upper mantle, the motions of the
seafloors spreading from the mid-ocean ridges and their densities
varying with age, gravitational forces, tidal forces, and
centrifugal forces. Scientists have differing theories.
Alfred Wegener thought that continents drifted because of centrifugal forces; today the picture is more complicated, involving convection in the upper mantle, the motions of the seafloors spreading from the mid-ocean ridges and their densities varying with age, gravitational forces, tidal forces, and centrifugal forces. Scientists have differing theories.
See also in The book of science:
Readings on wikipedia: