Transcript Fossils and the diversity of life

Early Mesozoic of Iowa
• No Triassic rocks in Iowa (surface or
subsurface)
• Jurassic rocks crop out in vicinity of Ft.
Dodge (Webster County)
– Ft. Dodge Formation is gypsum deposit
(evaporite)
– Iowa is 2nd largest gypsum producing state in
U.S. (1.65 million tons/year)
– Same age as dinosaur-bearing Morrison
Formation to the west
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Middle
Jurassic
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Ft. Dodge Formation
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Jurassic rocks
of midcontinent
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Cardiff Giant
• Man-like figure carved
from Ft. Dodge gypsum
• 10’ 4.5” long, 3’ wide,
2990 pounds
• Cooked up as a hoax in
1866 by George Hull
(visiting his sister in
Ackley, Iowa)
• Now preserved in
Cooperstown, New York
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Cardiff Giant
Sold for $37,500 and then put on display
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“There’s a sucker born every minute” (David Hannum)
Earth History,
Ch. 17of a fake
P.T. Barnum’s
fake
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Cretaceous World
142
Mesozoic Era
• Cretaceous System
was named in 1822
for deposits that are
“chalky” in many
parts of the world
• Duration of
Cretaceous Period is
longer than any other
65
Cretaceous
System
Jurassic
System
206
251
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Triassic
System
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Rise of the angiosperms
• Gymnosperms continued to dominate terrestrial
floras in Cretaceous (just as in Triassic and
Jurassic)
• Angiosperms initial appearance was in middle
Cretaceous time
–
–
–
–
Double-fertilization and enclosed seeds
Flowers (for attracting insects)
Co-evolution wih insects
Faster reproductive cycles
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Angiosperm diversification
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Rudist
reef
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Tyrannosaurus rex
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Warm-blooded Dinosaurs?
• Evidence in support of endothermy
– Cretaceous dinos lived in high latitudes
– Birds are endothermic, and birds are highly
specialized dinosaurs
– Dinosaur bone structure resembles that in
endothermic mammals
• Haversian canals
• But………
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Dinosaur bone structure
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Sue!!
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End-Cretaceous mass extinction
• Geologically instantaneous
• Non-avian Dinosaurs, mosasaurs,
plesiosaurs, rudists and ammonoids were
totally eliminated
• Angiosperms and gymnosperms suffered
big hits
• 90% of the species of calcareous
nannoplankton and planktonic
foraminifers were wiped out
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End-Cretaceous mass extinction
• Cause is controversial
– Asteroid impact
– Volcanism (Deccan Traps, India)
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End-Cretaceous mass extinction
• Mineral evidence for asteroid impact:
– Iridium anomaly at top of Cretaceous in both marine
and terrestrial rocks
• Iridium is rare on Earth, but abundant in meteorites
– Shocked quartz grains
• Welded planar fractures due to enormous pressure
– Microspherules
• Liquefied droplets of molten rock that cool rapidly
– Microscopic diamonds
• Again, high pressure minerals
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Iridium layer at Gubbio, Italy
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Mineral evidence
Iridium layer near
Drumheller in
southern Alberta,
Canada
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Mineral evidence
shocked quartz
microspherules
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End-Cretaceous mass extinction
• Further evidence for asteroid impact:
– The crater itself has been discovered in the Gulf
of Mexico, just offshore Yucatan Peninsula
• Chicxulub crater
– Central cavity (60 miles in diameter)
– Outer ring (120 miles in diameter)
– Magma that cooled after impact is dated at 65 ±
0.4 Ma, exactly same as end-Cretaceous
boundary
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Lab exam
“What is it?”
• Plants
• Mollusks
– Pelecypods
– Gastropods
– Ammonoids
– Ferns
– Sphenopsids
– Lycopsids
• Protists
– Fusulinids
• Echinoderms
– Crinoids
– Blastoids
• Goniatitic suture
• Ceratitic suture
• Ammonitic suture
– Belemnites
• Cnidarians (corals)
– Rugose
– Tabulate
– Scleractinian
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Chicxulub crater
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Radar image of Chicxulub crater
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Chicxulub crater
Gravity survey
data
trajectory
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Effects of the impact
• Perpetual darkness from atmospheric dust
• Short-term global refrigeration from dust
and aerosol particles (like “nuclear winter”)
• Acid rain from sulfur dioxide and water in
atmosphere
• Wildfires, especially in North America
• Long-term global warming from aerosols
that stayed in atmosphere
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Aftermath
• Although angiosperms suffered loss of
diversity, they recovered to become the
dominant flora
• With dinosaurs out of the way, mammals
diversified spectacularly in post-extinction
Cenozoic Era
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Continued break-up of Pangaea
• Remember: Pangaea began to break up
during early Mesozoic
– Triassic rifting between N. Africa and S.
Europe
– Jurassic rifting between N. America and S.
America; between N. America and Africa
– But, Gondwanaland remained intact
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Cretaceous paleogeography
• By late Cretaceous time:
– South America, Africa and India had become
discrete entities
– Only Australia and Antarctica remained
attached to one another
– Greenland split from North America
– Sea-level nearly at an all-time high
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Early Triassic
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Late Triassic
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Early Jurassic
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Middle Jurassic
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Late Jurassic
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Early Cretaceous
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Late early Cretaceous
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Late Cretaceous
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Cretaceous geology of
North America
• East coast, now a passive continental
margin, was mostly quiet
• West coast, a convergent margin, continued
to experience mountain building
– Sevier orogeny produced folding and thrusting
as far east as Wyoming; igneous activity in
California, Nevada, Idaho, and farther north
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Western U.S.
orogenies
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Nevadan Orogeny
Sevier Orogeny
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Cretaceous geology of
North America
• Interior seaway developed when continent was
flooded: Arctic Ocean joined with Gulf of Mexico
• Late Cretaceous rocks of interior seaway are
cyclic deposits produced by oscillation of
shoreline
– Nearshore sand facies
– Shallow marine shale facies
– Offshore chalk facies
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Late Cretaceous cyclic deposits
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Remember
this?
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