Earth ScienceEarth ScienceChapter 23Chapter 23Section 2Section 2

Mass extinction of the Paleozoic Era provided

opportunities for drastically different life forms The life forms filled empty niches Three Periods

Triassic Jurassic Cretaceous

Mesozoic Paleogeography

Breakup of Pangaea

Beginning of Era Single global ocean Single continent

Triassic Period Pangaea begins to

break apart Heat beneath the

continent caused it to expand

Brittle lithosphere began to crack

Cracks widened and continent began to split

Sea Ways

Mid ocean rift systems developed Seaways widened

Atlantic Ocean began forming Triassic Period

Mid-Ocean Rift systems partly responsible for rise

in sea level Hot magma displaced seawater as new rock was

formed Dropped, however, at the end of the Triassic

Period Desert like conditions formed in Western North

America Sea level rose again in Jurassic Period Continued to rise in Cretaceous Period

Changing Sea Level

Collision of continents forced mountains

upward

Mountain Building

Occurred in Western Laurentia

Subduction of oceanic Farallon Plate beneath Laurentia’s western margin Rocky Mountains Sierra Nevada Mountains

CordilleraAn extensive chain of mountains

Phase One

Occurred during late Jurassic and early Cretaceous Periods

Cordilleran Orogeny

Cordilleran Orogeny

Phase One: Steep Slow Subduction

Phase Two: Shallow faster

subduction Massive thrust faults

Phase Three Very fast, very shallow

subduction Tectonic activity inland Large vertical lifts

Mesozoic Life

Phytoplankton Microscopic

organism at the base of the marine food chain

Abundant during Cretaceous

Mesozoic Life

Plants As temperatures

warmed, plant life changes.

Tall cycad trees Seed plants with

true flowers Ginkgoes Pine trees conifers

Mesozoic Life

Terrestrial Animals Mammals

Late Triassic Same time as

dinosaurs Amniotic Eggs

Contain food and water required by developing embryo

Mesozoic Life

Dinosaurs Archosaurs

Unique skeletal structure

Speed and flexibility Hip structure allows

legs to be held underneath the body

(reptiles’ movement is more sprawling)

Devastated terrestrial dinosaurs

Most marine reptiles Plants

Today’s theory Massive and volcanism and large meteorite (10 km

diameter) impact caused climate problems Occurred at end of Cretaceous Caused long lasting greenhouse warming Layer of clay from that time contains high amounts

of iridium Rare on Earth but common in asteroids

Mass Extinction