Geology Reference
In-Depth Information
Scientists propose that toward the end of the Permian period (the last period of the Pa-
leozoic era), climate conditions were so warm all over the planet that ocean circulation
was stopped — with the result that no oxygen was brought into the deep sea, which es-
sentially suffocated marine life.
On the continents, the
Siberian Traps
— a massive outflowing of lava from volcanic fis-
sure activity in what is now northern Siberia — likely affected global climate conditions.
The release of gases associated with this type of volcanic activity may have been
enough to create a global greenhouse, warming temperatures enough to halt the
temperature-driven cycling of oxygen in the oceans.
Paving the way for dinosaurs
At the end of the Triassic period (the first period of the Mesozoic era), about 200 million
years ago, approximately 35 percent of the animal families became extinct. While this
event is the least dramatic of the five major extinctions, its cause is also still a mystery
to scientists.
This extinction event was likely spread over a long period of time. The
Central Atlantic
magmatic province
— a region of massive lava flows between the continents of South
America, Africa, and Europe as Pangaea split apart — was erupting, and evidence for cli-
mate conditions suggests the climate was on a rollercoaster from one extreme to the
next. This unsteady climate may have made it difficult for some species to adapt, result-
ing in their extinction.
The end-Triassic extinctions paved the way for dinosaur dominance. As other animal
groups died out, dinosaurs expanded to fill the empty niches, eventually covering every
environment on earth.
Demolishing dinosaurs: The K/T boundary
Possibly the most well-known mass extinction event is the one that ended the reign of
the dinosaurs at the end of the Cretaceous period (at the end of the Mesozoic era). In
the geologic record, the transition from the Cretaceous period to the Paleogene period
is well-marked by the disappearance of dinosaur fossils. As I explain in Chapter 20, some
dinosaurs are the ancestors of birds. These avian dinosaurs are the only ones who sur-
vived this extinction event. All the reptilian dinosaurs are found in rock layers below
this time period's geologic layer — not above it.
The geologic layer marking the boundary between the Cretaceous and Paleogene peri-
ods is called the
K/T boundary.
The K stands for the German word for Cretaceous,
