KT Boundary Extinction

1
K/T Boundary Extinction

• Cretaceous-Tertiary boundary (end of Mesozoic)
• Second largest mass extinction
• Half of life on Earth died out

2
K/T Boundary Extinction

• Tropical groups suffered most
• Seawater cooling global regression
• Many animals in decline before K/T boundary
• Mammals birds turtles crocodiles lizards
  snakes and amphibians unaffected

3
K/T Boundary

• Cretaceous-Tertiary (K/T) boundary (65 Ma)
• Second largest mass extinction in Earths history
• Half of life on Earth died out (3/4 species)

http//www.mhhe.com/earthsci/geology/mcconnell/gti
/metaphor.htm
4
What did Earth look like 65 Ma
5
Mass Extinctions Crises in the History of Life

• Greatest mass extinction took place at the end of
  the Paleozoic Era
• K/T extinction has attracted more attention
  because it affected dinosaurs

http//www.lpl.arizona.edu/SIC/impact_cratering/Ch
icxulub/totaldiversity.jpg
6
What caused the K/T extinction

• Volcanic eruptions
• Regression
• Climate change
• Impact
• All of the above

http//www.psi.edu/projects/ktimpact/ktimpact.html
7
What caused the K/T extinction

• Numerous hypotheses proposed to explain Mesozoic
  extinctions
• One proposal has become popular since 1980
• based on a discovery in Italy
• 2.5-cm-thick clay layer at the Cretaceous-Tertiary
  boundary with a remarkably high concentration of
  iridium
• High iridium concentrations have now been
  identified at many other Cretaceous-Tertiary
  boundary sites

8
Cretaceous-Tertiary Boundary

• K/T boundary site in Italy
• 2.5-cm-thick clay layer shows high concentration
  of iridium

9
Boundary Clay

• Closeup view of the boundary clay in the Raton
  Basin New Mexico

10
Boundary Clay

• Deep sea core
• Recovered by Joides Resolution in 1997

http//www.usssp-iodp.org/Education/poster.html
http//www.nmnh.si.edu/paleo/blast/k_t_boundary.ht
m
11
Iridium Anomaly

• Significance of the iridium anomaly
• iridium is rare in crustal rocks
• found in much higher concentrations in some
  meteorites
• Accordingly some investigators propose
• meteorite impact explains the anomaly
• meteorite perhaps 10 km in diameter
• impact set in motion a chain of events leading to
  extinctions

12
Iridium Anomaly Origin

• The iridium anomaly is real
• but its origin and significance are debated
• We know very little about the distribution of
  iridium in crustal rocks or how it may be
  distributed and concentrated
• Some geologists suggest that the iridium was
  derived from within Earth by volcanism but this
  idea is not very well supported by evidence

13
Boundary Sites

• Some Cretaceous-Tertiary boundary sites also
  contain
• soot
• shock-metamorphosed quartz grains

http//wwwdsa.uqac.ca/mhiggins/MIAC/chicxulub.htm
14
Meteorite Impact Crater

• Proposed meteorite impact crater
• Centered on Chicxulub on the Yucatán Peninsula of
  Mexico
• Discovered in 1950s interpreted to be volcanic

15
Chicxulub Crater
www.ig.utexas.edu GAIL CHRISTESON
16
Chicxulub Crater
Palaeo.gly.bris.ac.uk/Communication/Hanks/Fig6.htm
l
17
Chicxulub Crater
http//wwwdsa.uqac.ca/mhiggins/MIAC/chicxulub.htm
18
Chicxulub Crater
http//www.lpl.arizona.edu/SIC/impact_cratering/Ch
icxulubprpage/Chicxulub_drilling_hires.jpg
19
Impact Site

• Centered on the town of Chicxulub Yucatan
  Peninsula of Mexico
• The 180-km diameter structure lies beneath layers
  of sedimentary rock and appears to be the right
  age

20
Evidence at Chicxulub

• Shocked quartz
• Tsunami deposits and tektites small pieces of
  rock that were melted during the proposed impact
  and hurled into the atmosphere

http//wwwdsa.uqac.ca/mhiggins/MIAC/chicxulub.htm
21
What happened
The moment of impact 65 million years ago near
what is now the Yucatan Peninsula ...
... and the Chicxulub crater a few days later.
Note the inner ring.
http//www.space.com/scienceastronomy/planetearth/
asteroid_jello_001122.html
22
Impact Consequences

• According to the impact hypothesis
• 60 times the mass of the meteorite was blasted
  from the crust high into the atmosphere
• heat generated at impact started raging forest
  fires that added more particulate matter to the
  atmosphere
• Sunlight was blocked for several months
• caused a temporary cessation of photosynthesis
• food chains collapsed and extinctions followed

23
Acid Rain

• With sunlight greatly diminished Earths surface
  temperatures were drastically reduced adding to
  the biologic stress
• Another proposed consequence of an impact is that
  sulfuric acid (H2SO4) and nitric acid (HNO3)
  resulted from vaporized rock and atmospheric
  gases
• Both would have contributed to strongly acid rain
  that might have had devastating effects on
  vegetation and marine organisms

24
Terrestrial and Marine Extinctions

• Even if a meteorite did hit Earth did it lead to
  these extinctions
• If so both terrestrial and marine extinctions
  must have occurred at the same time
• To date strict time equivalence between
  terrestrial and marine extinctions has not been
  demonstrated
• The selective nature of the extinctions is also a
  problem

25
Impact Hastened Extinction

• In the terrestrial realm
• large animals were the most drastically affected
• but not all dinosaurs were large
• crocodiles close relatives of dinosaurs
  survived although some species died out
• Some paleontologists think that dinosaurs some
  marine invertebrates and many plants were
  already on the decline and headed for extinction
  before the end of the Cretaceous
• A meteorite impact may have simply hastened the
  process

26
Satisfaction

• In the final analysis Mesozoic extinctions have
  not been explained to everyones satisfaction
• Most geologists now concede that a large
  meteorite impact occurred but we also know that
  vast outpourings of lava were taking place in
  what is now India
• Perhaps these brought about detrimental
  atmospheric changes

27
Shallow Seas Withdrew

• Furthermore the vast shallow seas that covered
  large parts of the continents had mostly
  withdrawn by the end of the Cretaceous
• Mild equable Mesozoic climates became harsher and
  more seasonal
• But the fact remains that these extinctions were
  very selective and no single explanation
  accounts for all aspects of this crisis in life
  history