Download earth`s mass extinctions

Activity 1a: Earth’s Mass Extinctions
Unit C: Earth’s History
Learning Target:
1a)
I can distinguish between mass extinction and background extinctions and describe
their occurrence in geologic history using data.
EARTH’S MASS EXTINCTIONS
Mass extinction occurs when 40 % or more of the living plant and animal species become
extinct within a short period. Mass extinctions occur on a world-wide scale, and there have
been several mass extinctions in the history of the Earth. In fact, scientists believe, that
based on fossil records, about 99 % of species that ever lived are now extinct.
The most recent mass extinction, the Cretaceous extinction event, took place 65 million
years ago, when nearly all dinosaur species were destroyed. In the past 540 million years,
there have been five major mass extinctions. These were at the end of the following
periods: Triassic (about 208 million years ago), Permian (about 245 million years ago),
Devonian (about 360 million years ago) and the Ordovician (about 438 million years ago).
Mass extinctions may occur for any of the following reasons:
 Climate change - When the climate changes, many habitats are altered or
destroyed, causing the death of many plants and animals. Climate change may be
caused by volcanic eruptions, changes in the Earth’s orbit, imbalances in the
atmospheric gases and variations in solar output.
 Volcanic eruptions - These may be caused by movement of the continents and land
masses. Some of the larger volcanic eruptions lasted many years, pouring out lava
that piled up kilometers deep, killing everything it covered. Volcanoes also release
large amounts of gases into the atmosphere, changing the atmospheric gas balance,
and emitting greenhouse gases, which in turn leads to global warming and climate
change. Climate change then leads to environmental change.
 Changes in the Earth’s orbit - The way in which the Earth moves on its axis.
 Meteor/Asteroid Impact – A large meteor or asteroid impacting the Earth.
 Imbalances in atmospheric gases - Oxygen and carbon dioxide - changes in the
oxygen levels in the ocean.
 Variations in solar output - How much radiation and heat the sun is sending out.
 Changes in sea levels - During an ice age, sea levels drop globally as seawater is
taken up in the ice sheets. This is also called a glacial period. As the sea level drops,
many sea animals are forced to follow the retreating sea. If species are not able to
move to a new, favorable habitat when their old one is destroyed, they are simply
wiped out.
When conditions are warmer, this is known as an interglacial period, the ice sheets melt
causing sea levels to rise. A sudden rise in sea levels causes flooding on lowlands, drowning
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everything in those areas. Sea level changes are caused by climate changes as well as the
movement of the Earth’s crust.
DATA Analyze the data below describing mass extinction events.
Percent of
Species
Lost
MYA
Affected
Species
Ordovician
(Paleozoic Era)
85%
440mya
Marine
Species
Devonian
(Paleozoic Era)
83%
360mya
Marine
Species
Extinction
Permian
(Paleozoic Era)
96%
250 mya
Trilobites,
and other
marine
species, and
also
land plants,
amphibians,
and reptiles
Mostly
marine
Species, but
some
land species
Triassic
(Mesozoic Era)
80%
215
mya
Cretaceous/Tertiary
aka KT
(Mesozoic Era)
76%
65
mya
All Species,
especially
dinosaurs
70%
In the
next
30
years
Affects
species both
in the water
and on
land
Quaternary
(Cenozoic Era)
Reported by 1,100 United
Nations scientists in 2002
Global Outlook 3
Hypotheses
Glaciation, oxygen
depletion
Meteor impact,
volcanism,
glaciations,
Volcanism, meteor
impact, sea level
change, global
warming,
glaciation
Global cooling,
meteor
impact, sea-level
change, oxygen
depletion
Meteor impact,
volcanism,
continental
drift, mammal
competition
Human caused
effects
such as pollution,
over
population, global
warming, over-fishing
and deforestation
GRAPH
the % extinction vs. time period. Make sure you label axes and title your
graph. Do on separate graph paper.
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ANALYSIS QUESTIONS
1. Which hypothesis is the most common over all the mass extinction?
2. What appears to be one criterion that scientists use when defining the timing of
geologic periods?
3. Which mass extinction is the greatest?
4. Which mass extinction is the least?
5. Extinction normally occurs at what rate (how frequently)?
6. After a mass extinction, which organisms usually survive? Why?
7. Predict what would have happened if all of the early mammals living 66 million years
ago had died out in the Cretaceous mass extinction?
8. Many biologists propose that we are currently in a sixth major extinction. If this is
true, this mass extinction event may be the first caused by one of the Earth’s
inhabitants—humans. What human actions do you think may be the cause of the
increased rate of extinction today?
9. What data could you collect that would support the idea that we are currently at
the start of the sixth mass extinction?
10. In light of your answers to the previous questions, what would you predict to be the
long-term result of a sixth mass extinction?
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