Download Geologic Time and Mass Extinction

8-1 Notes - Geologic Time
and Mass Extinctions
Chapter 8, Lesson 1
Geologic Time Scale
• The changes that have occurred in Earth’s
history are recorded on a time line called the
geologic time scale.
• Each division is on the time scale is
determined by the presence and then
absence of index fossils.
Geologic Time Scale
• An index fossil is the remains of a species
that existed over vast regions of Earth for a
short period of time.
• Special criteria are used to identify index
fossils.
Geologic Time Scale
Geologic Time Scale
• No two divisions of time have the same
number of years.
• The largest divisions are eons, then eras,
periods, and epochs.
eons
eras
periods
eras
periods
periods
periods
epochs epochs epochs epochs epochs epochs epochs epochs
Geologic Time Scale
• We begin with
“Precambrian Time,”
which includes 3 eons:
– Hadean Eon
– Archean Eon
– Proterozoic Eon (ends 544
MYA with mass extinction)
Geologic Time Scale
• Next is the Phanerozoic
Eon, which is divided into
three eras:
Geologic Time Scale
– Paleozoic Era: (ancient
life) dominated by
invertebrate (no internal
skeleton) marine
organisms
Geologic Time Scale
– Mesozoic Era: (middle
life) dinosaurs and
mammals lived on land
Geologic Time Scale
– Cenozoic Era: (recent
life) modern mammals
and humans evolved;
continues today
Geologic Time Scale
• The Cenozoic Era is
divided into 3 periods:
– Paleogene Period
– Neogene Period
– Quaternary Period (now)
Geologic Time Scale
• The Quaternary Period
began 1.8 million years
ago and is divided into 2
epochs:
– Pleistocene Epoch (ended
about 8,000 years ago)
– Holocene Epoch (what we
are in now).
Mass Extinctions
• Mass extinction is the
dying off of many
species at one time.
• A greater abundance of
fossils in one rock layer
compared to other layers
indicates a mass
extinction.
Mass Extinctions
• Mass extinctions happen
over a great span of
time.
• 99% of all species are
now extinct.
Mass Extinctions
• A catastrophic event causes drastic change
in the numbers of organisms of species over
a short period in geologic time.
• Types of events that can cause mass
extinction include changes in climate,
volcanic eruptions, and asteroid impacts.
Climate Change
• There is evidence that some
mass extinctions were
caused by sudden climate
change.
• Species that cannot survive
a change in climate become
extinct.
• Climate change can be
caused by volcanic
eruptions or asteroid
impacts, and can result in
global warming or cooling.
Coral core samples
Climate Change
• Greenhouse gases (such
as carbon dioxide) in the
atmosphere may contribute
to global warming, which is
a global increase in
atmospheric temperature.
• Global warming causes a
decrease in oxygen levels
in water, and an increase
in sea levels.
May have been the cause for
the Devonian mass extinction
Climate Change
• Global cooling could lower sea levels as
more water is frozen in glacial ice.
• Less water means fewer warm, shallowwater environments.
May have initiated the Ordovician mass extinction
Volcanoes
• Eruptions can be explosive or non-explosive.
– The dust, ash, lava, and gas emitted from
volcanic eruptions can affect climate and
organisms.
A volcanic eruption is one hypothesis proposed to
explain the mass extinction at the end of the
Cretaceous period.
Mount Redoubt, Alaska
Volcanoes
• Non-explosive floods of molten basalt emit
the largest volume of matter of any
eruptions.
Geologic evidence shows that large basalt
flows occurred during the Permian and
Cretaceous mass extinctions.
Volcanoes
• The gases produced by basalt flows cause a
volcanic haze effect.
• Sulfur dioxide gas is released and acid
clouds form, preventing the Sun’s warming,
ultraviolet rays from reaching Earth.
Volcanoes
• Next, global cooling occurs over months
to tens of years.
• Over the next tens to thousands of years,
heat is trapped in the atmosphere, and
global temperatures increase.
Asteroid Impact
• Scientists believe a 10 km-wide (6.2 mi)
asteroid impact in Mexico may have
contributed to the Cretaceous mass
extinction.
• http://www.spaceweather.com/
Asteroid Impact
• Scientists propose that this impact sent
enough dust and materials into the
atmosphere to block sunlight.
• Global cooling after the impact turned to
global warming as carbon dioxide was
released from burning plants.
Asteroid Impact
• Evidence supports a mass extinction at the
end of the Cretaceous period because of
asteroids.
• But the impact did not cause all the
extinctions.
• Many species became extinct before the
impact, and the rate of extinction was
increasing before the impact.
8.1 Geologic Time and
Mass Extinctions
Which describes the divisions of the
geologic time scale in order of
longest to shortest units of time?
A eons, eras, periods, epochs
B eons, epochs, eras, periods
C epochs, eons, periods, eras
D epochs, eons, eras, periods
8.1 Geologic Time and
Mass Extinctions
What is the likely immediate
outcome of an explosive volcanic
eruption that sends dust into the
atmosphere?
A global warming
B global cooling
C basalt flows
D volcanic haze
8.1 Geologic Time and
Mass Extinctions
What type of eruption emits the
largest volume of matter?
A basalt flows
B explosive eruptions
C non-explosive eruptions
D volcanic haze
Which is not an effect of an asteroid
impact?
A sunlight blocked by dust
B basalt flows causing a complex
sequence of events
C carbon dioxide causing global
warming
D the death of primary producers
causing mass extinctions
Why have some paleontologists proposed
that asteroid impacts did not cause all the
mass extinctions at the end of the
Cretaceous period?
A There is no evidence of an asteroid impact
at the end of the Cretaceous period.
B Volcanic haze is a more likely cause.
C Many species were already extinct by the
time of the impact.
D The fossil record does not support a mass
extinction at the end of the Cretaceous
period.