The Paleozoic Era
 Paleozoic Paleogeography  the ancient geographic
setting of an area
o passive margin  edge of a continent along which
there is no tectonic activity
 Sea Level Δs in the Rock Record
o Shoreline deposition
 sand  sandstone
 clay  shale
 calcium carbonate (CaCO3)  limestone
 transgression  when sea level ↑ & causes the
shoreline to move inland; results in deeperH2O deposits on top of shallower-H2O
deposits
 regression  when sea level ↓ & causes the
shoreline to move seaward; results in
shallower-H2O deposits on top of deeper-H2O
deposits
o Evaporites
 rocks that have crystallized out of H2O that
is supersaturated w/dissolved minerals
 are deposited in the lagoons behind reefs
 mineral deposits  halite for road salt;
gypsum for plaster & drywall
 impermeability  oil deposits
o Glaciation
 transgressive & regressive cycles
 glaciers lower sea level
 Mountain Building
- Ordovician Period  Taconic Orogeny (mountains in
New York)
o Laurentia (core of modern-day North America)
deformed
 Ouachita Orogeny
 collided w/Gondwana (present-day Africa
& South America)
 Alleghenian Orogeny
 formation of the Appalachian Mountains
 @ the end  Pangaea
 Paleozoic Life
- multicellular organisms w/hard parts
o Cambrian explosion
 sudden appearance of a diverse collection of
organisms in the Cambrian fossil record
o Ordovician extinction
 more than ½ the marine groups that appeared
became extinct
 why?  glaciation
o Devonian extinction
 new marine groups: fish, other vertebrates,
tetrapods on land
 another extinction  ~ 50% of marine groups
 why?  global cooling/glaciers
o Terrestrial plants
 survived extinctions (seeds)
 coal deposits
 plants lived in swamps, died, sediment
added = coal
 large insects
o Permian Δs
 Permo-Triassic Extinction Event
 @ end, largest mass extinction ever;
extinction of ~ 95% of marine life-forms
 affected marine & terrestrial life
 > 65% of amphibians
 almost 1/3 of all insects
 why?  a combo of:
o ↓ in sea level
o extreme volcanism
o low atmospheric O2 levels
o meteorite impact
The Mesozoic Era
 Mesozoic Paleogeography
o Breakup of Pangaea
 middle of Triassic Period
 heat caused expansion  cracks
 climate was warm  no glaciers
o Seaways
 ocean flooded the rift valleys
 Atlantic Ocean & Mid-Atlantic Ridge formed
 Red Sea & Gulf of Aden  new seaways in
East Africa
o Δing sea level
 ↑ in sea level @ beginning
 sea level ↓ @ end of Triassic
 sea level ↑ again during Jurassic & continued
into Cretaceous
 Mountain Building
- along Laurentia’s west coast (not much on east
coast)
o Cordillera
 Spanish for “mountain range”
 3 phases:
1st phase  late Jurassic & early Cretaceous
 steep, slow subduction
 volcanism occurs near coast
 formed the Sierra Nevadas
2nd phase  during Cretaceous
 shallow, faster subduction
 massive thrust faults
 inland tectonic activity
 started forming Rocky Mountains
3rd phase –
 late Cretaceous & into Cenozoic
 very fast, very shallow subduction
 lack of volcanism
 tectonic activity moves inland w/large
vertical uplifts
 Mesozoic Life
- new marine organisms  large predatory reptiles
- phytoplankton  microscopic organisms that are
the basis of marine food chains; abundant during the
Cretaceous & the remains of their shell-like hard
parts are found in chalk deposits worldwide
o Plant life
 tall cycad trees  seed plants w/out true
flowers
 ginkgos, pine trees, & other conifers
 flowering plants in Cretaceous
o Terrestrial animals
 mammals appeared in late Triassic
 reptiles were dominant
 amniotic egg  egg w/a shell, providing a
complete environment for a developing
embryo
+ Dinosaurs
o most reptiles have a sprawling posture
o archosaurs  many dinosaurs had an
upright posture
o Mass extinction
 terrestrial dinosaurs, most marine reptiles,
plants, & many other organisms
 why?  combo of:
 massive volcanism (stressed climate)
 large meteorite impact @ end of
Cretaceous (@ least 10km in diameter)
o maybe in Mexico’s Yucatan Peninsula
o iridium  metal that is rare in rocks
@ Earth’s surface but is relatively
common in asteroids
The Cenozoic Era
 Cenozoic Paleogeography
~ 1.5% of Earth’s total history (~ the last 66 million
years)
o Cooling trend
 occurred when Australia split apart from
Antarctica during the Eocene
 caused by a Δ in ocean currents
o Miocene warming
 Antarctic ice cap melted
 was reversed in the mid/late Miocene 
Arctic Ocean began to freeze  set the
stage for the ice ages
o Ice ages
 started in late Pliocene & continued
throughout the Pleistocene
 @ peak, glaciers up to 3km thick covered
~ 1/3 of Earth’s land surfaces
 glaciers:
 carved out lakes & valleys
 dropped huge boulders
 left behind deposits of clay, sand, &
gravel
 Cenozoic Mountain Building
- erosion wore down the Rockies, but uplift continued
o Subduction in the West
 Farallon Plate began a steep subduction
beneath the Pacific Northwest  for the
Cascade Mountains (active volcanoes today)
 North American Plate + Pacific Plate = San
Andreas Fault
 transform boundary  little volcanism
o Basin & Range Province
 in SW US & northern Mexico
 consists of 100s of nearly parallel mountains
 formed when stresses in Earth’s crust
pulled it apart  still continues today
o Continental collisions
 Paleocene  Africa collided w/Eurasia
 created the Alps
 Paleogene  India crashed into Asia
 formed the Himalayas
o Tectonic forces continue
 are warm now  may become cooler in future
 some think that we may have another
supercontinent in 250 million years
 Cenozoic Life
- clams, sea urchins, & sharks survived the mass
extinction @ the end of the Cretaceous
- forests dominated the landscape
- climate cooled in the late Eocene  grasses
appeared
- late Oligocene  grasslands & savannas
- Age of Mammals
o Ice age mammals
 late Pleistocene  woolly mammoth & sabertoothed cat
 Homo sapiens  species to which modern
humans belong
o Humans
- bipedal  walking upright on 2 legs
- 1st bipedal humanlike primates appeared
~ 6 MYA during the late Miocene
- fossil remains of earliest modern humans
(Africa) are ~ 195,000 years old
 Migrations
 influenced by the ice ages of the late
Pleistocene
 North America’s 1st inhabitants  maybe
walked across the Bering Strait