Transcript CHICXULUB CRATER - University of Colorado Boulder

What Killed the Dinosaurs?
K/T Extinction Boundary
• 65 million years ago,
earth experienced a
global mass extinction
event: dinosaurs
disappeared
• that extinction defines the
boundary between the
Cretaceous and Tertiary
(abbreviated K and T)
geological periods and, a
broader scale, the
boundary between the
Mesozoic and Cenozoic
eras.
• The cause of the K-T extinctions is one of
the great mysteries in science, and
scientists have proposed many kinds of
theories to account for it. They range from
asteroid or comet impacts, volcanism, sea
level changes, supernova explosions, and
on and on.
What Is a Mass Extinction?
• an episode in evolutionary history where
more than 50% of all known species living
at that time went extinct in a short period
of time (less than 2 million years or so).
Permian-Triassic extinction
• Life on Earth nearly
was wiped out -- an
estimated 90% of all
species living at that
time were
extinguished.
• Trilobites were the
dominant marine
organism; wiped out.
CSI: Dinosaur Demise
• The Fossil Record - It's not perfect, gaps
• Time Resolution: gets worse with increasing
age; gradual decline of dinosaurs vs. a sudden
cataclysm is almost intractable
• Falsifiability - Sad but true: many “hypotheses”
about dinosaur extinction sound quite convincing
and might even be correct, but, as you know, are
not really science if they cannot be tested and
falsified if untrue.
Wrong Hypotheses That Have
Been Tested
• Dinosaurs got so darned big that they
crushed themselves
• Mammals outcompeted the dinosaurs
• Mammals ate all of the dinosaurs eggs
• Cosmic rays killed the dinosaurs
Common Ground
• There was global climatic change; the
environment changed from a warm, mild one in
the Mesozoic to a cooler, more varied one in the
Cenozoic
• Many organisms; both marine and terrestrial,
vertebrate and invertebrate; went extinct
• At or near the K/T boundary, there was iridium,
shocked quartz, tektites, and a soot layer was
found in many areas (evidence for widespread
forest fires), all consistent with a catastrophic
event
Iridium spike at K/T boundary
• Iridium is an element
that occurs in the
Earths crust in only
tiny proportions, but is
much more common
in chondrite
meteorites.
• Deep volcanoes also
a source
Shocked Quartz
• High pressures cause
what is known as shock
metamorphism, this
deforms the structure of
the quartz and creates
parallel laminar ripples.
• It is found all over the
world, not just locally.
• No other process on the
planet creates this type of
quartz.
• Meteors; volcanoes?
TEKTITES
• Tektites are naturally
occurring silica glass
• formed during the
impact of a meteor.
• Also formed from
volcanic eruptions
Cosmic Catastrophes
• Tektites are formed when
molten material is
injected into the
atmosphere and cools
before touching the
ground
• Volcanoes, meteors are a
source
• Psychically they are used
for extraterrestrial
communication, astral
travel, and lucid
dreaming.
Dinosaurs on Fire
• There is a large soot
layer associated with the
K/T boundary.
• This layer is consistent
with catastrophic fires
that may have swept the
surface of the earth at
this time.
• Such a fire would have
killed most large
terrestrial animals.
Nuclear Winter
• Lingering airborne
debris is believed to
have triggered
darkness and a
decline in the global
temperature
Intrinsic Gradualists: CSI
Volcanoes
Deccan Traps Volcanism
About 65 million years ago,
the mantle plume that
gave rise to the Reunion
hotspot volcano burned
its way through earth's
crust, flooding western
India and surrounding
areas with the Deccan
Traps flood basalts.
Deccan Traps Volcanism
• Rapid eruption of the vast Deccan Traps lava fields
would have flooded earth's surface with CO2,
overwhelming surficial systems and sinks, triggering
rapid K-T transition greenhouse warming, chemical
changes in the oceans (McLean, 1985a, b, c; 1988,
1995), and the K-T mass extinctions.
• This increased volcanism could have created enough
dust and soot to block out sunlight; contributing to the
climatic change.
• Source of Iridium; can explain iridium spike
• Source of tektites
• Shocked quartz; maybe a source
Plate Tectonics
• Major changes in the
organization of the continental
plates (continental drift) were
occurring at the K-T boundary.
• The oceans (especially the
Interior Seaway in North
America) were experiencing a
regression; they were receding
from the land. A less mild
climate would have been the
result, and this would have
taken a long time.
• Major plate activity is
consistent with major volcanic
activity
Extrinsic Catastrophists: CSI
Asteroids
Extrinsic Catastrophists
• This side of the controversy holds that the
ultimate cause of the K-T extinction was
extrinsic, meaning of an extraterrestrial
nature, and catastrophic, meaning fairly
sudden and punctuated. The main
hypothesis was proposed in 1980 by
(among others) Luis and Walter Alvarez,
geologists at the University of California at
Berkeley.
The Alvarez Hypothesis
•
•
•
A large extraterrestrial object
collided with the Earth, its impact
throwing up enough dust to cause
the climatic change.
The iridium layer is what prompted
the Alvarez team to blame an
asteroid impact for the extinction -asteroids and similar
extraterrestrial bodies are higher
in iridium content than the Earth's
crust, so they figured that the
iridium layer must be composed of
the dust from the vaporized
meteor.
No crater was found, but it was
assumed that one existed that
was about 65 million years old and
100 kilometers (about 65 miles) in
diameter.
Where Is the Smoking Gun?
Subducted? Evidence removed!
CHICXULUB CRATER
• Survey work related to oil
exploration in 1981 first
identified concentric rings
of gravitational anomalies
around the northwest
coast of Yucatan.
• Hildebrand (1991)
located two concentric
rings which suggested an
outer rim of 180 km.
The Smoking Gun!
• Some 65 million years
ago, a 10 to 12 km in size
asteroid or comet
crashed on the Yucatan
platform and formed the >
200 km in diameter
Chicxulub crater.
• If a 10km diameter object
impacted at the point at
which it struck it would
have a velocity of roughly
100,000 km/h.
Magnitude of Impact
• The K/T impact, as it
is now referred to,
resulted in 100 million
megatons of energy.
• Equivalent to the
energy of 300 million
nuclear weapons
Impact Forces
• Computer model of
the Chicxulub impact
showing the raising
fireball and CO2
plumes and ejecta
curtain material (from
Alvarez, Claeys and
Kieffer, Science 1995)
CONCLUSIONS
• There has been no settlement to the issue
so far, and no clear one is foreseeable.
Both sides claim to hold the majority of
proponents in science; it seems that
(greatly over- generalizing) many
paleontologists lean towards the intrinsic
side, while many astronomers and
physicists favor the extrinsic side, and
geologists are probably evenly split
between the two.