Transcript TEORIES OF MASS EXTINCTION

THEORIES OF MASS
EXTINCTION
Defining concepts
and
theories
Concepts
• Extinction
– All living individuals of a type (species) have died out
and do not exist anywhere on earth.
• Mass extinctions
– Periods of time when almost all of the life on Earth
died out.
• Why extinctions?
– Environmental disasters (e.g. meteor/ asteroid
impacts, severe volcanism, cosmic radiation
(exploding stars, super-lethal diseases )
– Failure to adapt to habitat or environmental changes
(e.g. fluctuating ice/ warm ages, global sea level
changes, continental drift )
THEORIES OF MASS
EXTINCTION
•
Continental drift
– The movement of separate parts of the earth’s crust (continental
plates) over a period of time
–
Alex du Toit, world
famous S,African
geologist,
pioneered this
theory in 1937
in his book “Our
wandering
continents”
1996-2007 EnchantedLearning.com
CLIMATE CHANGE
1.
Cooling of the atmosphere
• Ice age
– The cooling of the earth and the
formation of glaciers that covers a
part of the earth’s surface for a
period of time
 Formation of glaciers causes:
– Ocean levels to drop (due to water
trapped in glaciers, as ice)
– Decrease in O2 levels
– Increase in salt (mineral) content of
ocean
– Change in natural environments
Change in Climate
Knights
30 Year War
Industrial era
Vikings
– Takes place in
repeating cycles, i.e.
– Warm age followed
by Ice age
Average Warm Age
Little Ice Age
Years
Years
Graphic illustration of more recent warming and
cooling cycles.
• Volcano activity
– A possible cause for the cooling of the earth
due to large volumes of dust blown into the
atmosphere that blocks out the sun’s rays.
– Reduces solar radiation.
2.

Heating of the atmosphere
Tectonic plates led to changes in environments
Example: Extinction in Gondwanaland
(Clarens in the Free State)
– A mild climate with plenty of
water in large lake systems,
to a hot, dry desert climate.
– Warmer climate leads to
change in environmental
food chains.
• Disease
– Change in climate - influences presence of
disease causing organisms in environments
and their effect on the survival of other
organisms.
– Also theory of
extraterrestrial viral
and bacterial invasion
Extraterrestrial theories
• Explosion of a stars
– Influence on earth radiation levels and
destroys ozone layer
– May have influenced extinctions (no
scientific proof as yet)
• Meteorite / asteroid
collisions with earth
– Meteorite –Large rocklike mass that
falls from outer space onto earth –
larger than 1 km (Vredefort and Parys)
– Asteroid –off course orbiting
fragments of a failed planet in the
Asteroid Belt between Mars & Jupiter
– Meteor – small fragments, burn up in
space, called shooting stars
– Comet – revolves in elliptic orbit
around the sun, has solid nucleus +
gaseous tail
– Gamma radiation – from dying stars
METEORITES
• Meteors (shooting stars)
burn and glow when they
enter earth’s atmosphere.
• Most disintegrate into
ashes and debris.
• Some remain intact,
known as Meteorites, to
create craters on earth.
• Can destroy life forms by
shutting off sunlight for
months / years.
Meteorites and Extinction
• Growing evidence
that meteorites are
responsible for some
major mass
extinctions.
• Meteorites may have
added the final blow
to species that were
already weakened by
global temperature
changes, etc.
What happened to Dinosaurs?
Scientific evidence:
• Meteorite impact melted
rocks in 200km diameter
crater near Mexico.
• Sediments deposited by
enormous tsunamis (tidal
waves) along coastline.
• Caused acid rain and
severe global cooling.
• 70% of known fossils,
including dinosaurs,
wiped out (65 Ma).
Impact in Gulf of Mexico
Dinosaur extinction
• 200 km diameter crater in
Mexican Gulf (near Chicxulub)
• Caused by 10km diameter
meteorite impact of 65 million
years ago.
• Impact caused acid rain, ash
that blocked out the sun for
months, severe global cooling
(nuclear winter).
• Increase in atmospheric CO2,
resulting in global warming,
final blow to dinosaurs & many
other Cretaceous species.
VREDEFORT DOME
• Crater 10 km in diameter.
• Impact speed of 10 – 15
km /sec.
• 16 km into earth’s crust.
• Blast of impact caused
70km3 of rock to be
vapourised and to spread
into the atmosphere.
• Location:100 km South
of Johannesburg between
Vredefort and Parys.
5 MAJOR EXTINCTIONS
1.
2.
3.
4.
5.
End of Ordovician
End of Devonian
End of Permian
End of Triassic
End of Cretaceous
Time line of each extinction?
Which was the most severe?
Which was the least severe?
Which is most recent?
SIXTH EXTINCTION
• The impact of man
on earth – human
overpopulation
– Current rate of
extinction of species
estimated at three
species / hour or about
30 000 species per
year.
Global warming
– The big melt down
• Rising ocean levels as
polar ice caps and glaciers
melt
• Increasing global
temperatures
• Change in seasonal
patterns
• More frequent occurrence
of weather extremes e.g.
increase in droughts &
floods
• Migration of disease
vectors for malaria,
bilharzia and cholera
Human influence on the drastic
increase in extinction of species
• Industrial activity
– Pumping greenhouse
gases into atmosphere
– Climate change
– Pollution
• Change of large parts of
natural environments
into food-producing
agricultural areas & living
spaces due to
overpopulation and
widespread habitat
destruction.
RECENT EXTINCTIONS
•
•
•
•
Kwagga
Bluebuck
Quagga
Many frog species
Near extinction of
Bontebok and Sable
Antelope
• Many Cycad species
• Some Proteas and
bulbs.
Something to think about
• The modern climate is
depicted by a question mark,
reflecting the uncertainty of the
future climate. If humans were
not present on earth, the
climate would likely cool off
into an ice age, as it has many
times in the past. However,
humans are disrupting earth's
carbon cycle by burning fossil
fuels, and releasing
greenhouse gases into the
atmosphere. By the Hansen et
al. (1988) "Scenario A," the
climate could warm 7.2°F
(4°C) by the year 2050 should
a worst-case materialize
Human Impact
Humans
McLean, D. M., 1991, A climate change
mammalian population collapse mechanism, in
Kainlauri, E., Johansson, A., Kurki-Suonio, I.,
and Geshwiler, M., eds., Energy and
Environment: Atlanta, Georgia, ASHRAE, p. 93100.
Conservation and controlling growth of human population is a
must to prevent 6th extinction – that of mankind