Download Chapter 8, Lesson 1 - Jefferson School District

Chapter 8, Lesson 1
Geologic Time and Mass
Extinctions
Time Scale
• Eons
(Phanerozoic & Precambrian)
• Eras
(Paleozoic, Mesozoic, Cenozoic)
• Periods
(ex. Jurassic)
• Epochs (currently-Holocene)
Mass Extinctions
Definition: The dying off of many different species of
organisms over a short period of geologic time
(as much as a million years)
•Fact: 99 % of all species that have lived
on earth are now extinct.
•Most extinctions occur 1 species at a
time
•Several units on the geologic time scale
begin and end with a mass extinction.
Causes of Mass Extinctions
Catastrophic Events: An event that causes a drastic
change in the number of organisms of one or more
species over a short period in geologic time.
3 types of catastrophic events
1) Climate Change
2) Volcanoes
3) Asteroid Impacts
Fact: Not all catastrophic events cause mass extinction
Climate Change
sudden changes in climate that can cause mass extinctions
Global Warming
Burning of fossil fuels, such as coal and oil, adds
greenhouse gases, like carbon dioxide, to the
atmosphere. Many scientists think greenhouse gases in
the atmosphere contribute to global warming, a global
increase in atmospheric temperature. If the overall
temperature of the atmosphere increases, the
temperature of the oceans also increases. Because
warm water holds less oxygen than cold water, global
warming could cause a decrease in oxygen levels in the
water. If the oxygen levels drop in shallow waters,
where most organisms live, mass extinctions could
occur. Global warming could also raise sea levels.
Water from melting glaciers would flow into the
oceans, causing sea levels to rise. Geologists have
found evidence of warm temperatures, a rising sea
level, and oxygen-poor waters flooding shallow-water
areas. Some scientists think global warming might
have been the cause.
Global Cooling
Mass extinctions could also be
caused by global
cooling, an overall decrease in
atmospheric temperatures. Global
cooling could lower sea levels as large
amounts of water are frozen
in glacial ice. Less water in the
oceans would mean fewer warm,
shallow-water environments. With
fewer warm-water environments,
there would be less space to support
marine ecosystems.
Global cooling appears to have
initiated the Ordovician mass
extinction event.
Volcanoes
Explosive and non-explosive eruptions emitting dust, ash, lava,
and gas which affect climate and organisms
The Haze Effect:
Suspended particles,
such as dust and ash,
can block out the
earth's sunlight, thus
reducing solar
radiation and lowering
mean global
temperatures
The eruption of Pinatubo in the Philippines, 12 June 1991,
the largest volcanic eruption since 1912. The Toba
eruption 73,000 years ago would have looked rather
similar, only very much larger: while Pinatubo erupted 4
cu. km of ash, Toba produced at least 800 cu. km.
Asteroids
• What if a large comet or asteroid hits......
• The Shoemaker-Levy Comet Impact with Jupiter gave us a way to test
theories of extinction by asteroid impact.
Jupiter
The events on Jupiter
agreed closely with the
most popular theory for the
extinction of the dinosaurs.
In this theory, a dramatic
impact on the Yucatan
coast of a comet or
asteroid about 10 km in
diameter 65 million years
ago killed 16 percent of
marine families, 47 percent
of marine genera (the
classification above species)
and 18 percent of land
vertebrate families,
including the dinosaurs.
Although most dinosaurs
were probably killed off in
the initial event where
debris superheated the
upper atmosphere, the after
events would have been very
destructive too. There would
have been huge tidal waves
from the shock, and possibly
the impact triggered large
earthquakes that caused
even more. Afterwards, the
upper atmosphere would have
been saturated with the
soot and gases from the
massive fires, resulting in
years of climate change that
included severe acid rain.