Download Chapter 23 Paleozoic, Mesozoic, & Cenozoic Eras

3/19/12 - Bellringer
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Chapter 23
Paleozoic, Mesozoic, &
Cenozoic Eras
23.1 – Paleozoic Era
Phanerozoic Eon
• "visible life."
• 542 million years ago to the present
• Consists of three eras
– Paleozoic = "ancient life" (542-251 million
years ago)
– Mesozoic = "middle life" (251-65.5 million
years ago)
– Cenozoic = "recent life" (65.5 million years
ago to the present)
http://higheredbcs.wiley.com/legacy/college/levin/0471697435/chap_tut/chaps/chapter10-01.html
http://www.geol.umd.edu/~tholtz/G102/102lpal1.htm
Paleozoic Era
– Early Paleozoic = Cambrian, Ordovician and
Silurian periods
– Late Paleozoic= Devonian, Mississippian,
Pennsylvanian, and Permian periods
• Long periods of sedimentation and mountain
building.
http://higheredbcs.wiley.com/legacy/college/levin/0471697435/chap_tut/chaps/chapter10-01.html
Paleogeography
• Ancient geographic setting
of an area defined by
breakup of supercontinent
Rodinia
• Multicellular life evolved
with increasing complexity
http://higheredbcs.wiley.com/legacy/college/levin/0471697435/chap_tut/chaps/chapter10-01.html
Passive Margin
• No tectonic activity along the
edge of a continent
• Laurentia split from Rodinia
– Located near equator
– Covered by shallow tropical
sea
– No mountain ranges forming
– Completely surrounded by
passive margins
Shoreline deposition
• Evidence of sea level changes
• Tides wash sand and sediment ashore
– forms sandstone
• Deposit clay offshore
– Forms shale
• Calcium carbonate
from sea water and
as organisms die,
falls to seafloor
– Forms limestone
Transgression
• Movement of shore-line inland as sea level
rises
– As level rises & falls, deposition shifts
• Rise in water level, causes water to move
inland
– Deep water deposits overlying shallow water
deposits in vertical rock sequences
Regression
• Sea level falls
– Shore moves out to the sea
• Shallow water deposits overlie deep water
deposits in vertical rock sequences
• Evidence is found in stacked sequence of
limestone-shale-sandstone
Evaporites
• Rocks that have crystallized out of water
that is saturated with dissolved minerals
• Associated with fossilized reefs
– Reefs are made from carbonate skeletons of
organisms
– Form in long, linear mounds parallel to
continents or islands
– Absorb energy from waves that crash against
them
Glaciation
• Sea level transgressed and regressed
over 50 times during late Paleozoic
• Reasons for change:
– Climate and glaciation cycles
– Crustal subsidence and uplift
– Sedimentation rates
– Plate motions
In-class Assignment/Homework
• Transgression/Regression Worksheet
23.1 Notes continued
Mountain Building
• During Ordovician Period, Laurentia
collided with Taconic Island Arc
– Mountains began to rise in what is now
northeastern North America
– Event known as Taconic Orogeny
Taconic Mountains
• Added new land and
an active volcanic
zone along eastern
margin of Laurentia
– Evidence found in
New York’s Taconic
Mountains
http://geoscape.nrcan.gc.ca/toronto/escarp_e.php
Deformation
• During Silurian Period, Laurentia collided
with another landmass
• Caused folds, faults and igneous
intrusions to already deformed rocks
Ouachita Orogeny
• During Carbonifierous Period southeastern
Laurentia collided with Gondwana
– Gondwana = large landmass that eventually
formed southern continents
• Formed Ouachita Mountains for Arkansas
and Oklahoma
http://www.rockhoundingar.com/geology/ouamtns.html
Ouachita Orogeny
• Caused crust to uplift inland as far as
present-day Colorado
• Formed ancestral Rockies Mountains
http://jan.ucc.nau.edu/~rcb7/Ancestral_Rockies.jpg
Alleghenian Orogeny
• Gondwana continued to push against
Laurentia
• Appalachian Mountains began to form
– Quite possibly taller than Himalayans when
formed
• Last mountain-building event of Paleozoic
– Leads to formation of Pangaea
In-class Assignment/Homework
• 23.1 Study Guide
– #2 = Laurasia = Laurentia
– Skip #8, 15, 16
– #6 = 650
– #13 & 14 = 649
– #17 & 18 = 650
23.1 Notes, part C
Paleozoic Life
• Multicellular
organisms went
through extensive
diversification
• First appearance of
organisms with hard
parts
http://higheredbcs.wiley.com/legacy/college/levin/0471697435/chap_tut/images/nw0237ann.jpg
Cambrian explosion
• Geologically rapid diversification of a large
collection of organisms in the Cambrian
fossil record
– Burgess Shale
• Spectacular array of fossil organisms with
hard parts
Ordovician extinction
• More than half of marine groups that
appeared during Cambrian became extinct
• Evidence of glacial deposits found
– When water freezes, sea level drops
Ordovician extinction
• Most marine animals live in shallow waters
on continental shelves
• When sea level is high = many places for
animals to live
• During regression, continental shelves
become too narrow for life to survive
Devonian Period
• Following Ordovician, marine life
recovered and new species evolved
– Tremendous diversification of vertebrates
(animals with backbones)
– Fish and first appearance of tetrapods on land
• Another extinction takes place
Devonian extinction
• Eliminates approximately 50% of marine
groups
• Caused by global cooling
• Evidence of glaciers on some continents
http://universe-review.ca/I10-35-extinction.jpg
Plant Life
• Ordovician and Devonian extinctions had
little effect on land organisms
• Simple land plants begin to appear
• First plants with seeds diversified
– Seeds contain own moisture and food source
– Made them more enabled to survive change
in environments
Permian Period
• Largest mass extinction occurred
• Affected both marine and terrestrial
organisms
– Eliminated nearly 95% of marine groups
– More than 65% of amphibians and 1/3 of
insects did not survive
Permian Extinction
• How did it happen?
• Many causes
– Dramatic drop in sea level from Pangaea
formation draining shallow seas
– Extreme volcanism
– Low atmospheric oxygen levels
– A Meteorite impact
In-class Assignment/Homework