Chapter 7
Earth and the Terrestrial
Worlds
WHAT DO YOU THINK?
1.
Why are Venus (too HOT), Mars (too
COLD) and Earth (just right!) so different
in their atmospheres?
2.
Could Mars have supported life long
ago? How do we know?
3.
Is life known to exist on Mars today?
Final Exam Essay Question

Describe the atmospheres of Venus, Earth,
and Mars. Why are these three atmospheres so
different?
Mercury
craters
smooth plains
cliffs
Venus
volcanoes
few craters
Radar view of a twinpeaked volcano
Mars
some craters
volcanoes
riverbeds?
Moon
craters
smooth plains
Earth
volcanoes
craters
mountains
riverbeds
Why have the planets turned
out so differently, even though
they formed at the same time
from the same materials?
Goals: Understanding Earth
as a Planet

Why is Earth geologically active?

What processes shape Earth’s surface?

How does Earth’s atmosphere affect the
planet?
Why is Earth geologically
active?
Earth’s Interior

Core:
Highest density; nickel
& iron

Mantle:
Moderate density;
silicon, oxygen,
etc.

Crust:
Lowest density;
granite, basalt, etc.
Terrestrial Planet Interiors

Applying what we learn about Earth’s
interior to other planets tells us what their
interiors are probably like.
Why do water and oil separate?
A.
B.
C.
D.
Water molecules repel oil molecules
electrically.
Water is denser than oil, so oil floats
on water.
Oil is more slippery than water, so it
slides to the surface of the water.
Oil molecules are bigger than the
spaces between water molecules.
Why do water and oil separate?
A.
B.
C.
D.
Water molecules repel oil molecules
electrically.
Water is denser than oil, so oil
floats on water.
Oil is more slippery than water, so it
slides to the surface of the water.
Oil molecules are bigger than the
spaces between water molecules.
Differentiation
Gravity pulls highdensity material to
center
 Lower-density
material rises to
surface
 Material ends up
separated by
density

Thought Question
What is necessary for differentiation to occur in a
planet?
A.
B.
C.
D.
E.
It must have metal and rock in it.
It must be a mix of materials of different
density.
Material inside must be able to flow.
All of the above.
b and c.
Thought Question
What is necessary for differentiation to occur in a
planet?
D.
It must have metal and rock in it.
It must be a mix of materials of different
density.
Material inside must be able to flow.
All of the above.
E.
b and c!
A.
B.
C.
Lithosphere

A planet’s outer
layer of cool,
rigid rock

Lithosphere
“floats” on
warmer, softer
rock beneath.
Thought Question
Do rocks s-t-r-e-t-c-h?
A.
B.
C.
No—rock is rigid and cannot deform
without breaking.
Yes—but only if it is molten rock.
Yes—rock under strain may slowly
deform.
Thought Question
Do rocks s-t-r-e-t-c-h?
A.
B.
C.
No—rock is rigid and cannot deform
without breaking.
Yes—but only if it is molten rock.
Yes—rock under strain may slowly
deform.
Strength of Rock

Rock stretches when
pulled slowly but
breaks when pulled
rapidly.

The gravity of a large
world pulls slowly on
its rocky content,
shaping the world into
a sphere.
Heat Drives Geological Activity
Convection: hot rock
rises, cool rock falls.
One convection cycle
takes ~100 million
years on Earth.
Sources of Internal Heat
1.
Accretion
releases
gravitational
potential energy
2.
Differentiation
3.
Radioactivity
Heating of Interior over Time

Accretion and
differentiation
when planets
were young

Radioactive
decay is most
important heat
source today
Cooling of Interior

Convection

Conduction

Radiation
Cooling of Interior

Convection transports
heat as hot material rises
and cool material falls

Conduction transfers
heat from hot material to
cool material

Radiation sends energy
into space
Thought Question
What cools off faster?
A.
A grande-size cup of Starbucks coffee
B.
A teaspoon of cappuccino in the same
cup
Thought Question
What cools off faster?
A.
A grande-size cup of Starbucks coffee
B.
A teaspoon of cappuccino in the same
cup
Thought Question
What cools off faster?
A.
A big terrestrial planet
B.
A tiny terrestrial planet
Thought Question
What cools off faster?
A.
A big terrestrial planet
Brrrr!
B.
A tiny terrestrial planet
Role of Size

Smaller worlds cool off faster and harden earlier

Moon and Mercury are now geologically “dead”
Surface Area to Volume Ratio

Heat content depends on volume.

Loss of heat through radiation depends on
surface area.
2
4r
3 divided
 Timesurface
to cool
depends
on
surface
area
area to volume ratio =

4
by volume:
r 3 r
3


Larger objects have a smaller ratio and cool
more slowly.
Planetary Magnetic Fields
Moving charged particles create magnetic fields.
A planet’s interior can create magnetic fields if
- it is electrically conducting, &
- it is circulating and/or rotating.
Earth’s Magnetosphere
Earth’s magnetic fields protects us from
charged particles from the Sun.
The charged particles can create aurorae
(“Northern lights”).
Thought Question
If the planet core is cold, do you expect it to
have magnetic fields?
A.
Yes, refrigerator magnets are cold, and
they have magnetic fields.
B.
No, planetary magnetic fields are
generated by moving charges around,
and if the core is cold, nothing is moving.
Thought Question
If the planet core is cold, do you expect it to
have magnetic fields?
A.
Yes, refrigerator magnets are cold, and
they have magnetic fields.
B.
No, planetary magnetic fields are
generated by moving charges around,
and if the core is cold, nothing is
moving.
How do we know what’s inside a planet?

“P” waves
push matter
back and
forth.

“S” waves
shake matter
side to side.
How do we know what’s inside a planet?

P waves go
through Earth’s
core, but S
waves do not.

Earth’s core
must have a
liquid outer layer.
What processes shape Earth’s
surface?
Geological Processes

Impact cratering
—

Volcanism
—

Eruption of molten rock onto surface
Tectonics
—

Impacts by asteroids or comets
Disruption of surface by internal stresses
Erosion
—
Changes made by wind, water, or ice
Impact Cratering

Most cratering happened
soon after solar system
formed.

Craters about 10 times
wider than objects that
made them.

Small craters greatly
outnumber large ones.
Impact Craters
Meteor Crater (Arizona)
Tycho (Moon)
Volcanism

Molten rock
(magma) finds path
through lithosphere
to surface.

Molten rock is
called lava after it
reaches the
surface.
Lava and Volcanoes
Runny lava makes flat
lava plains.
Slightly thicker lava Thickest lava makes
makes broad shield steep stratovolcanoes.
volcanoes.
Outgassing

No, not from cows…
Outgassing

Volcanism also releases gases from Earth’s
interior into the atmosphere.
Tectonics



Convection of the mantle creates stresses in the crust
called tectonic forces.
Compression forces make mountain ranges.
A valley can form where the crust is pulled apart.
Erosion

Weather-driven processes that break
down or transport rock.

Processes include
—
—
—
Water/Ice movement by glaciers & rivers
Atmospheric Movement by wind, storms
Cyclic heating/cooling
Erosion by Water

The Colorado
River continues
to carve the
Grand Canyon.
Erosion by Ice

Glaciers
carved the
Yosemite
Valley.
Erosion by Wind

Wind wears
away rock and
builds up sand
dunes.
Erosional Debris

Erosion can
create new
features by
depositing
debris.
How does Earth’s atmosphere
affect the planet ?
Effects of Atmosphere on Earth
1.
Erosion
2.
Makes the sky blue!
3.
Radiation protection
4.
Greenhouse effect
Thought Question
Why is the sky blue?
A.
The sky reflects light from the oceans.
B.
Oxygen atoms are blue.
C.
Nitrogen atoms are blue.
D.
Air molecules scatter blue light more than
red light.
E.
Air molecules absorb red light.
Thought Question
Why is the sky blue?
A.
The sky reflects light from the oceans.
B.
Oxygen atoms are blue.
C.
Nitrogen atoms are blue.
D.
Air molecules scatter blue light more than
red light.
E.
Air molecules absorb red light.
Why the sky is blue

Atmosphere scatters
blue light from the
Sun, making it
appear to come from
different directions.

Sunsets are red
because less of the
red light from the Sun
is scattered.
Earth’s atmosphere absorbs light at most wavelengths.
Radiation Protection

All X-ray light is
absorbed very high in
the atmosphere.

Ultraviolet light is
absorbed by ozone
(O3) ~ 30 miles high
The Greenhouse Effect
The Greenhouse Effect on
Earth
Greenhouse
effect:
Certain
molecules let
sunlight through
but trap escaping
infrared photons.
(H2O, CO2, CH4)
Greenhouse Gases

Any gas that absorbs infrared

Greenhouse gas: often molecules with two
different types of elements (CO2, H2O, CH4)

Not a greenhouse gas: molecules with one or
two atoms of the same element (O2, N2)
Greenhouse Effect: Bad?
The Earth is much warmer because of the
greenhouse effect than it would be without
an atmosphere…but so is Venus.
The Goldilocks Question!
Why is Venus too hot, Mars
too cold, and Earth just right??
The Goldilocks Question!
Why is Venus too hot, Mars too cold, and
Earth just right??
• Distance?
• Venus is too close, Mars too far away
from the Sun, and Earth just right?
• Size?
• Mars too small to retain its heat?
• Life?
• Earth’s oceans and life forms
tranform the planet?
The Role of Distance?
Earth is located at an optimal distance
from the Sun for liquid water to exist…
Distance can’t be the only factor!
We now know MARS had liquid water,
too!
The Role of SIZE?
Earth is large enough for internal heat to
drive volcanoes and create an
atmosphere
SIZE can’t be the only factor!
Earth and Venus are almost the same
size, and seem identical in composition!
The Role of Atmosphere?
Earth is able to recycle CO2 and retain
water in its atmosphere…
A Combination of Factors…
Earth is habitable because it is:

large enough to remain geologically active,

at the right distance from Sun so oceans
could form, AND
 able to
retain water in the atmosphere to help
cycle CO2
The Greenhouse Effect
Greenhouse Gases

Any gas that absorbs infrared light

Greenhouse gas: often molecules with two
different types of elements (CO2, H2O, CH4)

Not a greenhouse gas: molecules with one or
two atoms of the same element (O2, N2)
The Greenhouse Effect on
Earth
Greenhouse Effect: Bad?
The Earth is much warmer because of the
greenhouse effect than it would be without
an atmosphere…but so is Venus.
How can Earth “regulate” CO2?
Goldilocks & the Earth’s
CO2 cycle
What does COKE have to do with
Astronomy??
Goldilocks & the Earth’s
CO2 cycle
Carbonation was not initially part of Coke!
Goldilocks & the Earth’s
CO2 cycle
Carbonation occurs naturally when pushing
water with CO2 gas!
Carbon Dioxide Cycle
•
How does our
atmosphere &
tectonics
combine to
regulate
temperatures?
•
How does life
play a role?
Carbon Dioxide Cycle
Step 1: Evaporation/Rain
1
•
Liquid water evaporates
•
Condenses into clouds
in lower atmosphere
•
Rain falls through
atmosphere forming
Carbonic Acid (H2CO3)
 CO2 gas is absorbed
Carbon Dioxide Cycle
Step 2: Mineral Erosion by Acid Rain
•
Carbonic Acid (H2CO3)
in rivers erodes rocks
•
Carbonate (CO32-) ion
picked up in minerals
washed to ocean
•
Calcium easily absorbed
2
 CO2 is carried to oceans
Carbon Dioxide Cycle
Step 3: Tying Carbon into Rocks &
Life!
3
•
Calcium from rocks
forms CaCO3 (Calcium
Carbonate)
•
CaCO3 = Limestone
•
CaCO3 = Coral, Mollusk
shells!
 CO2 accumulates on
seafloor
Carbon Dioxide Cycle
Step 4: Tectonics & Subduction!
4
•
Tectonics gradually pulls
seafloor down
•
CaCO3 broken back into
CO2 & other minerals
 CO2 now inside crust
Carbon Dioxide Cycle
Step 5: Volcanic Outgassing!
•
5
Eventual Volcanic
Activity pushes CO2
back into atmosphere
 CO2 now in
atmosphere again!
Carbon Dioxide Cycle
•
“Recycle” CO2
from atmosphere
to crust to
atmosphere over
time
•
Estimate ~25
million years or
more for this to
occur globally
Carbon Dioxide Cycle
“Feedback Loop”
Suppose evaporation stopped,
during an ice age….
What would happen over time?
Carbon Dioxide Cycle
Feedback Loop: Ice Age
•
1
•
•
No evaporation
No Rain
NO CO2 gas absorbed
Carbon Dioxide Cycle
Feedback Loop: Ice Age
No evaporation
•
No Rain
•
NO CO2 gas absorbed
But…
•
Tectonic Activity &
Volcanoes continue!
•
Gradual CO2
concentration increase!
•
1
5
Carbon Dioxide Cycle
Feedback Loop: Ice Age
•
1
5
•
•
•
•
Tectonic Activity &
Volcanoes continue!
Gradual CO2
concentration increase!
More Greenhouse
Effect => warmer!
Ice Melts!
Cycle restored!
Long-Term Climate Change

Changes in Earth’s axis tilt might lead to
ice ages.

Widespread ice tends to lower global
temperatures by increasing Earth’s
reflectivity.
Long-Term Climate Change
CO2 from outgassing will build up if oceans are
frozen, ultimately raising global temperatures
again.
Carbon Dioxide Cycle
“Feedback Loop”
Suppose CO2 in our
atmosphere traps too much
heat, and we heat up?
What would happen over time?
Carbon Dioxide Cycle
Feedback Loop: Global Warming
•
Liquid water
evaporates FASTER
•
MORE Rain
1
5
 MORE CO2 gas is
absorbed
Carbon Dioxide Cycle
Feedback Loop: Global Warming
•
1
•
5
•
•
Volcanoes continue at
“normal” rate…
Gradual CO2
concentration
decrease!
Less Greenhouse
Effect => cooler!
Cycle restored!
Earth as a “Living” Planet

What unique features on Earth are
important for human life?

How is human activity changing our
planet?

What makes a planet habitable?
What unique features of Earth
are important for life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
What unique features of Earth
are important to human life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
Earth’s distance from the
Sun and moderate
greenhouse effect make
liquid water possible.
What unique features of Earth
are important to human life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
PHOTOSYNTHESIS
Climate stability
(plant life) is required to
make high concentrations
of O2, which also
produces the protective
layer of O3.
What unique features of Earth
are important to human life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
Plate tectonics
are an important
step in the
carbon dioxide
cycle.
Continental Motion

Idea of
continental drift
was inspired by
puzzle-like fit of
continents

Mantle material
erupts where
seafloor
spreads
Plate Motions
Continental Motion

Motion of continents can be
measured with GPS
Tectonics & Seafloor Recycling

Seafloor is recycled through a process
known as subduction
Carbon Dioxide Cycle
•
How does our
atmosphere &
tectonics
combine to
regulate
temperatures?
•
How does life
play a role?
Carbon Dioxide Cycle
Step 1: Evaporation/Rain
1
•
Liquid water evaporates
•
Condenses into clouds
in lower atmosphere
•
Rain falls through
atmosphere forming
Carbonic Acid (H2CO3)
 CO2 gas is absorbed
Carbon Dioxide Cycle
Step 2: Mineral Erosion by Acid Rain
•
Carbonic Acid (H2CO3)
in rivers erodes rocks
•
Carbonate (CO32-) ion
picked up in minerals
washed to ocean
•
Calcium easily absorbed
2
 CO2 is carried to oceans
Carbon Dioxide Cycle
Step 3: Tying Carbon into Rocks &
Life!
3
•
Calcium from rocks
forms CaCO3 (Calcium
Carbonate)
•
CaCO3 = Limestone
•
CaCO3 = Coral, Mollusk
shells!
 CO2 accumulates on
seafloor
Carbon Dioxide Cycle
Step 4: Tectonics & Subduction!
4
•
Tectonics gradually pulls
seafloor down
•
CaCO3 broken back into
CO2 & other minerals
 CO2 now inside crust
Carbon Dioxide Cycle
Step 5: Volcanic Outgassing!
•
5
Eventual Volcanic
Activity pushes CO2
back into atmosphere
 CO2 now in
atmosphere again!
Carbon Dioxide Cycle
•
“Recycle” CO2
from atmosphere
to crust to
atmosphere over
time
•
Estimate ~25
million years or
more for this to
occur globally
Carbon Dioxide Cycle
“Feedback Loop”
Suppose evaporation stopped,
during an ice age….
What would happen over time?
Carbon Dioxide Cycle
Feedback Loop: Ice Age
•
1
•
•
No evaporation
No Rain
NO CO2 gas absorbed
Carbon Dioxide Cycle
Feedback Loop: Ice Age
No evaporation
•
No Rain
•
NO CO2 gas absorbed
But…
•
Tectonic Activity &
Volcanoes continue!
•
Gradual CO2
concentration increase!
•
1
5
Carbon Dioxide Cycle
Feedback Loop: Ice Age
•
1
5
•
•
•
•
Tectonic Activity &
Volcanoes continue!
Gradual CO2
concentration increase!
More Greenhouse
Effect => warmer!
Ice Melts!
Cycle restored!
Long-Term Climate Change

Changes in Earth’s axis tilt might lead to
ice ages.

Widespread ice tends to lower global
temperatures by increasing Earth’s
reflectivity.
Long-Term Climate Change
CO2 from outgassing will build up if oceans are
frozen, ultimately raising global temperatures
again.
Carbon Dioxide Cycle
“Feedback Loop”
Suppose CO2 in our
atmosphere traps too much
heat, and we heat up?
What would happen over time?
Carbon Dioxide Cycle
Feedback Loop: Global Warming
•
Liquid water
evaporates FASTER
•
MORE Rain
1
5
 MORE CO2 gas is
absorbed
Carbon Dioxide Cycle
Feedback Loop: Global Warming
•
1
•
5
•
•
Volcanoes continue at
“normal” rate…
Gradual CO2
concentration
decrease!
Less Greenhouse
Effect => cooler!
Cycle restored!
What unique features of Earth
are important to human life?
1.
2.
3.
4.
Surface liquid water
Atmospheric oxygen
Plate tectonics
Climate stability
The CO2 cycle acts like a
thermostat for Earth’s
temperature.
These unique features are intertwined:
•
•
•
•
Plate tectonics create climate stability
Climate stability allows liquid water
Liquid water is necessary for life
Life is necessary for atmospheric
oxygen
How many other connections between
these can you think of?
How is human activity
changing our planet?
Dangers of Human Activity

Human-made CFCs in the atmosphere destroy
ozone, reducing protection from UV radiation.

Human activity is driving many other species to
extinction.

Human use of fossil fuels produces
greenhouse gases that can cause global
warming.
Global Climate Change

Earth’s average temperature has
increased by 0.5°C in the past 50 years.

The concentration of CO2 is rising rapidly.

An unchecked rise in greenhouse gases
is leading to global climate change.
CO2 Concentration

Global temperatures
have tracked CO2
concentration for the
last 500,000 years.

Antarctic air bubbles
indicate the current
CO2 concentration is
at its highest level in
at least 500,000
years.
CO2 Concentration
Most of the CO2 increase has happened
in last 50 years!
Modeling of Climate Change

Build climate models
based on current/past
data

Models suggest
recent temperature
increase is consistent
with human
production of
greenhouse gases.
What makes a planet habitable?
Located at an optimal distance from the
Sun for liquid water to exist
What makes a planet habitable?
Large enough for geological activity to
release and retain water and
atmosphere
Planetary Destiny
Earth is
habitable
because it is
large enough to
remain
geologically
active, and it is
at the right
distance from
the Sun so
oceans could
form.
Planetary Destiny
Earth is habitable because it is large enough to
remain geologically active, and it is at the right
distance from the Sun so oceans could form.