A series of mountain-building events occurred along the western
coast of North America during the Triassic, when all the continents
were part of the supercontinent Pangea. These events were the result
of oceanic plates subducting under the continent, carrying landmasses
that collided with and attached to the continent, creating chains
of Andes-like mountains. It was also during the Triassic that Pangea
began to break apart. In the meantime, dinosaurs evolved and, as
throughout the history of the planet, meteorites hit the Earth.
One of the largest impact craters visible today, the Manicouagan
crater, was formed in this period.
Later in the Triassic, the supercontinent of Pangaea began to break
apart. The end of the Triassic is marked by a major extinction event
that killed 20% of marine animals and many of the species on land
that competed with the dinosaurs. With much of their competition
gone, dinosaurs became the major land animals while the predatory
ammonites proliferated in the oceans.