chapter. 6 Mass extinction and biodi. loss -.pptx

Paleontology
Lecturer @ SNU: Abdirizak Abdullahi
CHAPTER 6

https://www.slideshare.net/ChiragChjnrs/mass-
extinction-78240039

An extinction event ( also known as a mass extinction or biotic
crisis) is a widespread and rapid decrease in the a mount of life
on earth.
Extinctions occur when the last individual of a species
dies out.
 Functional Extinctions occur when individuals remain
but the odds of sustainable reproduction are low
WHAT IS EXTINCTION?

 Mass Extinction: Points in geologic time where a large number
of species become extinct
Although not certain, scientists link many of these mass
extinctions to asteroid, comet or meteoroid impact events
It is believed that an object from outer space that left a crater in
southern Mexico wiped out the dinosaurs and many other species
about 65 million years ago
 MASS EXTINCTIONS
WHAT IS MASS EXTINCTION?

WHAT IS EXTINCTION?
 Extinction may also be defined as the disappearance of any evolutionary lineage (from
populations to species to higher taxonomic categories) because of death or the genetic
modification of every individual.
 EXTINCTION ELIMINATES AN ENTIRE SPECIES…..
 Where a lineage has changed such that a new (daughter) species is recognised,
the extinction of the original (parent) species may also be called
pseudoextinction.
 The new and original species are known as chronospecies.
 Extinction may be regarded as the result
of failing to adapt to environmental
changes.
 it is also a natural process.

WHAT’S A MASS EXTINCTION?
 a sharp decrease in the number of species in a relatively short period of
time.
 Mass extinction is an event that eliminates half or more of the
species in a region
 There different ways a mass extinction can occur including…
Asteroids
Comets
Global warming
Ice age
And more…

EXTINCTIONS ARE NATURAL.
Extinctions occur naturally.
Nearly all of the species that have existed on earth have gone extinct.
There have been 5 major mass extinctions in geological history.
Recovery from these events took millions of years.

HOW MANY MASS EXTINCTIONS HAVE THERE BEEN?
Five major mass extinctions in the history of the planet

BACKGROUND EXTINCTION AND EXTINCTION EVENTS
The extinction rate that is normal in the fossil record is known as
background extinction.
 Extinction events are relatively short (in terms of geological time) periods with
greatly increased extinction rates.
 A mass extinction event must eliminate >60% of species in a relatively short period
of geological time with widespread geographical and taxonomical impacts.
Mass extinction events are important because of the disruptive effect they have on
the way biodiversity develops.
 The principle subdivisions of geologic time are identified by distinctive fossils and
major faunal breaks (extinction events) were used as the boundaries.
 Mass extinction events may occur periodically.

Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
THE
GEOLOGICAL
TIME
SCALE

SOME QUANTIFIED EFFECTS OF MASS EXTINCTIONS
Table 6.1: The Effects on Skeletonized Marine Invertebrates of the ‘Big Five’ Mass
Extinctions (modifieda from p713, Futuyma 1998)
A. Modifications come from Anderson (1999), Lévêque & Mounolou
(2001), Broswimmer (2002), Futuyma (2005) and Wikipedia
Contributors (2006c).
B. Time periods are given for the older mass extinctions because the literature gives variable
dates.
C. The species percentages are estimated from statistical analyses of the numbers of species per
genus.
Extinction
Event
Age
(x106
years)b
Families
(%)
Genera
(%)
Species
(%)c
End Cretaceous 65 16—17 50 76 ± 5
End Triassic 208 22—23 50 80 ± 4
End Permian 245 51—57 84 95 ± 2
Late Devonian 365 19—22 55 83 ± 4
End Ordovician 440 26—27 61 85 ± 3

WHEN DO EXTINCTIONS OCCUR?
 Extinctions occur when the environment of a species changes faster than the species
can adapt.
 In other words, a species’ adaptations are no longer sufficient in allowing that species to
acquire and compete for resources.
 Extinctions can be local, widespread, or global.

CAUSES OF MASS EXTINCTIONS
 Most of the extinction events are likely to have been caused by a combination of factors.
 Postulated consequences of the asteroid strike that caused the end Cretaceous (K/T)
mass extinction include acid rain, widespread fires, climate cooling due to dust and smoke,
earthquakes and increased volcanic activity elsewhere in the world and a tsunami (an
enormous tidal wave).
 The aforementioned consequences would have caused ecological disruption leading to
further extinctions.

THE ORDOVICIAN-SILURIAN EXTINCTION
 The earliest of the five mass extinctions.
 439 million years ago
 Caused by the movement of Gondwana into the south polar region. This led to global cooling,
glaciation and consequent sea level fall.
 Acombination of lowering sea level and glacially driven cooling are likely driving agents for the
Ordovician mass extinction.
 a drop in sea level as glaciers formed, then by rising sea levels as glaciers melted.
Impacts on life forms:
 Plants, insects and tetrapods had not yet developed so they were not affected.
 Marine organisms affected: brachiopods, cephalopods, echinoderms, graptolites,
solitary
 corals and trilobites.
  Killed about 25% of marine families
  Killed 60% of marine generafe Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.

THE END ORDOVICIAN
MASS EXTINCTION
Suggested causes include:
 Climate change,
 Adrop in sea level,
 Asteroid or comet impacts,
 A gamma ray burst.

THE LATE DEVONIAN MASS EXTINCTION
The second of the five mass extinctions.
Happened about 365 million years ago.
Impacts on life forms:
• About 22% of marine families were killed
• About 55% of the genera were killed
Insects and tetrapods had not yet developed so they were not affected.
 Plants: the rhyniophytes decreased.
 Marine organisms affected: ammonoids, brachiopods, corals, agnathan fish,
placoderm fish, ostracods and trilobies.

Not clear if it is 2 large mass extinctions or a series of small
extinctions
Suggested causes include:
 Climate change,
 Multiple asteroid impacts.
Suggested that a asteroid impact was the prime cause

PERMIAN-TRIASSIC EXTINCTION
The third and biggest of the five mass extinctions happened about 245
million years ago.
Informally called the “the Great Dying”
It was the most severe extinction caused
Most likely due to volcanic eruption,
an asteroid impact
or a near by super nova.

 96% of all marine species were killed
 70% of terrestrial vertebrate were killed
 the extinction took a few million years
 Impacts on life forms:
 Plants: the previously dominant Ottokariales (glossopterids) became extinct.
 Insects: about two thirds (2/3) of the insect families became extinct and six insect
orders disappeared.
 Tetrapods affected: amphibians and mammal-like reptiles
 Marine organisms affected: benthic foraminifera, brachiopods, bryozoans,
echinoderms,
 44% of fish families, all graptolites, solitary corals and all trilobites.
Normal levels of biodiversity did not become present until 6 million years after the
end of the Permian

THE END PERMIAN MASS
EXTINCTION
Suggested causes include:
1. climate change,
2. a drop in sea level,
3. massive carbon dioxide (CO2) poisoning,
4. oceanic anoxia,
5. the explosion of a supernova,
6. asteroid or comet impacts,
7. plate tectonics during the formation of

END TRIASSIC EXTINCTION
The fourth of the five mass extinctions.
Happened about 208 million years ago.
Impacts on life forms:
Plants: several orders of gymnosperms were lost and the Umkoma- siales (Dicroidium)
became extinct.
Insects: not severely affected.
Tetrapods affected: some reptile lineages – the mammal-like reptiles (therapsids) especially.
Marine organisms affected: ammonites, ammonoids, bivalves (Molluscs), brachiopods,
corals, gastropods and sponges.
 22% of Marine families
 52% of marine genera
 Vertebrate deaths unknown

THE END TRIASSIC MASS
EXTINCTION
 Caused by gradual climate change, sea level
fluctuations that resulted massive floods.
 Massive volcanic or lava erupting from
central Atlantic province – an event that
triggered the opening of the Atlantic Ocean
 The volcanism may have lead to deadly global
warming
Suggested causes include: one or more
asteroid/comet impacts, climate change
and volcanic activity.

THE END CRETACEOUS MASS EXTINCTION
 The final and best known of the five mass
extinctions.
 Happened about 65 million years ago.
 Impacts on life forms:
 Plants: debatably up to 75% of species.
 Insects: not severely affected.
 Tetrapods affected: 36 families from 3 groups
(dinosaurs (all non-avian), plesiosaurs and pterosaurs).
 Marine organisms affected: ammonites, ammonoids,
cephalopods, bivalves, foraminifera, icthyosaurs,
mosasaurs, plackton and rudists.
 Suggested causes include: asteroid/comet impact,
climate change and volcanic activity.

CRETACEOUS-TERTIARY
EXTINCTION

K-T EXTINCTION
 K : Abbreviation for Cretaceous Period,
derived from the German name Kreidezeit
while
 T : Abbreviation for the Tertiary Period
 historical term for period of time covered by the
Paleogene and Neogene periods
 Also referred to as the Cretaceous– Paleogene
extinction event
 Approximately 65 million years ago
 Associated with geological signature
 K–T boundary: thin band of sedimentation found in
various parts of world
http://evolution.berkeley.edu/evolibrary/imag
es/interviews/extinction_graph3.gif
http://en.wikipedia.org/wiki/K–T_boundary

ALVAREZ HYPOTHESIS
Mass extinction of dinosaurs (etc.) caused by impact of
large asteroid on Earth 65 million years ago
Named for Nobel-prize winning physicist Luis Alvarez
who first suggested theory in 1980, along with geologist
son Walter Alvarez and chemists Frank Asaro and Helen
Michels
http://en.wikipedia.org/wiki/Alvarez_hypothesis

EVIDENCE?
K-T boundary sedimentary band all over
the world has iridium ranging from 20-160
times normal amount.
Iridium is rare in Earth’s crust, but
abundant in asteroids/comets
Also found chromium isotopic anomalies
similar to those found
in carbonaceous chondrites, along with
shocked quartz granules and tektites.
Alvarez, L.W. Science. 1980, 208, 1095-1108.
tektites
carbonaceous
chondrites

ALVAREZ IMPACT
Able to calculate size of meteor
Would have to be 10-15 km in
diameter (size of Mars moon
Deimos, or Manhattan)
Impact of that size would have an
incredible amount of energy
1 x 108 megatons, 2 million times
greater than most powerful
thermonuclear bomb tested!
Alvarez, L.W. Science. 1980, 208, 1095-1108.

CHICXULUB CRATER
http://www.lpl.arizona.edu/undergrad/classes/spring2011/Hubbard_206/Lectures4/Apr19.htm

CHICXULUB CRATER
Impact site buried underneath Yucatán
peninsula in Mexico, discovered by
geophysicist Glen Penfield in the late 1970s.
Took about 20 years to fully investigate crater,
with help from Alan Hildebrand.
Evidence for impact:
Shocked quartz
Tektites
Gravity anomaly
http://en.wikipedia.org/wiki/Chicxulub_crater

ALVAREZ IMPACT
Created sunlight blocking dust cloud
Affects photosynthesis, leading to extinction of plants,
phytoplankton and other organisms dependent on it.
Sulfur aerosols (12 years to dissipate)
10–20% reduction of solar transmission
Global firestorms exacerbated by high O2
concentration
Increase in CO2, greenhouse effect once cloud settled
Reduced global temperature (impact winter)
Acid rain (relatively minor impact) + megatsunamis!
Kring, D.A. Astrobiology. 2003, 3, 133-152

ALVAREZ IMPACT
2007- Hypothesis that impact forming Chicxulub
crater was caused by asteroid from Baptistina
family of asteroids
The collision would have released the same energy
as 100 teratonnes of TNT (420 ZJ), over a billion
times the energy of the bombs dropped on
Hiroshima and Nagasaki
Still controversy on whether a single impact was
the sole cause.

Deccan Traps
http://johnstodderinexile.files.wordpress.com/2006/10/deccan-flood-basalts.jpg

DECCAN TRAPS
Large igneous province located on the
Deccan Plateau of west-central India
One of the largest volcanic features on
Earth
Multiple layers of solidified flood basalt
more than 2,000 m thick with an area of
500,000 km2 and a volume of 512,000 km3
http://en.wikipedia.org/wiki/Deccan_Traps

POTENTIAL CAUSES
One or more catastrophic events?
Asteroid impacts?
Increased volcanic activity?
Several impact craters and massive volcanic
activity have been dated to the approximate time
of extinction
These events would have released massive
amounts of dust and ash released into the
atmosphere
Reduced surface sunlight
Hindered photosynthesis
Disruption of Earth’s biosphere
MacLeod, N. J. Geo. Soc. 1997, 154, 265-292.

THE END CRETACEOUS MASS
EXTINCTION
 The final and best known of the five mass extinctions.
 Happened about 65 million years ago.
 Impacts on life forms:
 Plants: debatably up to 75% of species.
 Insects: not severely affected.
 Tetrapods affected: 36 families from 3 groups (dinosaurs (all
non-avian), plesiosaurs and pterosaurs.
 Marine organisms affected: ammonites, ammonoids,
cephalopods, bivalves, foraminifera, icthyosaurs,
mosasaurs, plackton and rudists.
 Suggested causes include: asteroid/comet impact, climate
change and volcanic activity.
 The occurrence of an impact event has been verified.

Suggested causes K-T MASS
EXTINCTION
The first and the most favored theory is that an
asteroid hit somewhere in the gulf of Mexico in the
Yucatan Peninsula 65 million years ago. The Asteroid
impact is site is called the CHICXULUB.
http://rst.gsfc.nasa.gov/Sect18/originals/Fig18_17.jpg

 Volcanic eruptions have also been theorized to have killed of the
dinosaurs. When volcanoes erupt they send clouds of dust,
sulfuric acid, and poisonous gas that would have made it
impossible to breath. This would result in the blocking of
sunlight and a severe climate change. This would have been
nearly impossible to survive in this environment

DIVERSIFICATION AND SPECIATION
AFTER MASS EXTINCTIONS
SURVIVING SPECIES TAKE OVER VACANT HABITATS
AND RESOURCES
SPECIATION TAKES EVERY 100 TO 100,000 YEAR
10 TO 10,000 NEW SPECIES PER YEAR

PERIOD ONSET MAJOR EVENTS ME
Paleozoic Cambrian 540 Ma most animal phyla present, diverse algae
Ordovician 490 Ma first jawless fishes, animal diversification 1st
Silurian 445 Ma first bony fishes, colonization of land
Devonian 420 Ma first insects and amphibians, fish diversify 2nd
Carboniferous 355 Ma extensive forests, first reptiles, insects radiate
Permian 290 Ma reptiles radiate, insects are diverse 3rd
Mesozoic Triassic 250 Ma early dinosaurs, first mammals, marine inverts. diversify 4th
Jurassic 200 Ma first birds, diverse dinosaurs
Cretaceous 145 Ma flowering plants and mammals diversity, dinosaurs
continue diversification
5th
Cenozoic Tertiary 65 Ma radiation of mammals, birds, flowering plants, pollinating
insects
Quaternary 2 Ma humans evolve, extinctions of large mammals

IS THERE A POTENTIAL SIXTH
MAJOR EXTINCTION?
SPECIES ARE BECOMING EXTINCT AT A RATE
OF
 ABOUT
4000/YEAR
100/DAY
 1 SPECIES EVERY 15 MINUTES

 What do you think, are we in the midst of a mass extinction???
http://ircamera.as.arizona.edu/NatSci102/NatSci102/images/endearth4.jpg

2050
 50% of all species on the planet will be either endangered
or extinct
* Habitat destruction
* Global Warming
 25% mammalian species
 15% bird species

HUMAN EXTINCTION?
If all species will become extinct, then human extinction
is also inevitable.
 The risks of human extinction are not considered very great by the
average person despite knowledge of many possible mechanisms of
extinction.
 The ‘Doomsday argument’ proposed by Brandon Carter suggests that we
should be suspicious of low values for the probability of human
extinction.
 Lester Brown provides evidence that the current methods of food
production are unsustainable.
 Julian Simon believes that the present technology is enough to pro-vide
for a continuously expanding population for the next 7 billion years.
 Both cannot be right. Logic and the ‘Doomsday argument’ suggest that it
would be sensible to act on Brown’s evidence.

chapter. 6 Mass extinction and biodi. loss -.pptx

chapter. 6 Mass extinction and biodi. loss -.pptx

Recommended

Recommended

More Related Content

Similar to chapter. 6 Mass extinction and biodi. loss -.pptx

Similar to chapter. 6 Mass extinction and biodi. loss -.pptx (20)

More from MuuminCabdulle

More from MuuminCabdulle (15)

Recently uploaded

Recently uploaded (20)

chapter. 6 Mass extinction and biodi. loss -.pptx