Geography Reference
In-Depth Information
butional patterns directly, but new mountains, oceans, and land barriers
change the climatic patterns on the landmasses.
Continental drift was originally proposed by Wegener (1912) and met
with enormous opposition. Plate tectonics was a mechanism that explained
continentaldriftandmadeitacredibletheory.Seafloorspreadingisbelieved
to be caused by great convection currents that bring material to the surface
from the hot interior of the earth, inducing the movement of tectonic plates.
These are the moving units at the surface of the earth and may contain con-
tinental masses or may consist of ocean floor. The movement of the plates
had great relevance for organisms. The movement of the continents relative
to the poles and the equator caused climatic changes. Additionally, shallow
epicontinental seas covered parts of the continents or formed seas within
them during the Jurassic and Cretaceous periods, forming barriers to dis-
persal. The splitting of continents also altered the patterns of water circu-
lation in the oceans. Furthermore, the appearance of new mountains as a
result of continental drift had dramatic consequences for biotic distributional
patterns.
A major feature of the Late Paleozoic and Mesozoic was the supercon-
tinent of Gondwana. It included the land areas that later became South
America, Africa, Madagascar, Antarctica, Australia, New Zealand, and India.
Its northern edge broke up into a series of minor landmasses or terranes,
which moved north and joined the southern edge of Eurasia to form south-
ern Europe, Tibet, and two separate portions of China (Cox and Moore
1998). By the Silurian (435-410 mya), there were three continents:
Euramerica (North America and Eurasia), Siberia, and Gondwana. In the
Late Carboniferous to Early Permian (300-270 mya) Euramerica joined
Gondwana, andinthe Late Permian (260mya)Siberia joined this landmass,
forming the world continent of Pangaea. Pangaea soon divided into two
landmasses: Laurasia in the north and Gondwana in the south. From the
Jurassic to the Cretaceous, Laurasia was penetrated by epicontinental seas
and Gondwana started to break up into separate continents. India separated
from the rest of Gondwana in the Early Cretaceous. In the Late Cretaceous,
Europe and Asia were separated by the Obisk Sea; the former was con-
nected to eastern North America (the Euramerican landmass), and the latter
was connected to western North America (the Asiamerican landmass).
Table 8.1
