Shifting Continents and Greenhouse
By the beginning of the Cretaceous, the
of Pangea had broken up into two smaller continents.
The northern one, Laurasia, included what are today the continents
of Europe, Asia, and North America. The other, Gondwana, was
formed from the southern landmasses of present-day Africa, South America, Australia,
India, Antarctica, and Madagascar. By the earliest Late Cretaceous (100 million
years ago), rising sea level had caused the Western Interior Seaway
to flood the central United States. This seaway extended from Texas into British
Columbia. By 94 million years ago, the Tethys Ocean covered
most of southern Europe, separating Laurasia from
Southern Europe was represented only by a chain of islands. By this time, Laurasia
and Gondwana had begun to split into the continents we know today. Africa and
South America had nearly completely separated from each other, and India was
an island in the Indian Ocean moving toward southern Asia. The climate was also
much warmer than it is today, with no ice caps in polar regions.
The Pangean breakup led to an increase in seaways and shorelines, which may
have affected the diversification of terrestrial plants and animals by creating
several isolated continental regions. In addition, rapid seafloor spreading
during the final breakup of Pangea caused a tremendous release of carbon
dioxide gas (CO2). This began in the Early Cretaceous
and led to dramatic global climate warming that culminated about 92 million
years ago, with nearly tropical temperatures extending to very high
latitudes (polar regions). Such extreme warmth resulted in ice-free polar
regions that were populated by dinosaurs, diverse forests and abundant insects.
Fossils of crocodile-like champsosaurs, which could not tolerate
extended periods of sub-freezing temperatures, have been found in Late Cretaceous
sediments well north of the Arctic Circle. Conditions much warmer
than those of today lasted into the Eocene.