middle of Wyoming. The Nevadan orogeny produced the Sierra Nevada in
California (Fig. 156) during the middle to late Jurassic.
The breakup of Pangaea compressed the ocean basins, causing a rise in sea
level and a transgression of the seas onto the land. In addition, an increase in vol-
canism flooded the continental crust with vast amounts of basalt.The rise in vol-
canic activity also increased the carbon dioxide content of the atmosphere,
resulting in a strong greenhouse effect that led to the warm Mesozoic climate.
Continental breakup and dispersal might have also contributed to the
extinction of many dinosaur species.The shifting of continents changed global
climate patterns and brought unstable weather conditions to many parts of the
world. Massive lava flows from perhaps the most volcanically active period
since the early days of Earth might have dealt a major blow to the climatic and
ecological stability of the planet.MARINE TRANSGRESSION
Throughout most of Earth’s history, several crustal plates constantly in motion
reshaped and rearranged continents and ocean basins.When continents broke
up, they overrode ocean basins, which compressed the seas and made them less
confined to their basins, thereby raising global sea levels several hundred feet.
The rising sea inundated low-lying areas inland of the continents,dramatically
increasing the shoreline and shallow-water marine habitat area, which in turn
supported many more species.Figure 156A view
across Kern Canyon, with
Kaweah Peaks Ridge in
the background in the
Sierra Nevada, Sequoia
National Park,Tulare
County, California.
(Photo by F. E. Matthes,
courtesy USGS)
Historical Geology