Transcript Earth and the Terrestrial Worlds

Chapter 7
Earth and the Terrestrial Worlds
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, when they formed
at the same time from nearly the
same materials?
7.1 Earth as a Planet
Our Goals for Learning
• Why is Earth geologically active?
• What processes shape Earth’s
surface?
• How does Earth’s atmosphere affect
the planet?
Why is Earth geologically active?
Why is Earth geologically active?
Short answer: the Earth is big enough to still have a
hot interior.
So what do we know about the interior of the Earth
and why is it hot?
Internal Structure, by density
lithosphere
Internal structure, by rock
strength
The lithosphere is the cool rigid rock that
forms a planet’s outer layer: the crust and
some of the mantle.
The lithosphere “floats” on the lower layers.
The thickness of the lithosphere
controls many geologic processes
Internal Structure of the
Terrestrial Planets
Sources of Internal Heat
1) Gravitational
potential energy of
accreting
planetesimals
2) Differentiation
3) Radioactivity
Why do water and oil separate?
A. Water molecules repel oil molecules
electrically.
B. Water is denser than oil, so oil floats on
water.
C. Oil is more slippery than water, so it slides
to the surface of the water.
D. Oil molecules are bigger than the spaces
between water molecules.
Why do water and oil separate?
A. Water molecules repel oil molecules
electrically.
B. Water is denser than oil, so oil floats on
water.
C. Oil is more slippery than water, so it slides
to the surface of the water.
D. Oil molecules are bigger than the spaces
between water molecules.
Differentiation
• Layers controlled by density
• Highest density on the bottom (sinks)
• Gravity sorts materials by density.
• Differentiation converts gravitational
potential energy to heat.
What cools off faster?
A. A grande-size cup of Starbucks coffee
B. A teaspoon of capuccino in the same cup.
What cools off faster?
A. A grande-size cup of Starbucks coffee
B. A teaspoon of capuccino in the same
cup.
What cools off faster?
A. A big terrestrial planet.
B. A tiny terrestrial planet.
What cools off faster?
A. A big terrestrial planet.
B. A tiny terrestrial planet.
Why?
Heat Drives Geological Activity
Convection: hot rock
rises, cool rock falls.
1 cycle takes 100
million years on
Earth.
A large planet…
•
•
•
•
Is still warm inside
Has a convecting mantle
Has a thinner, weaker lithosphere
Has molten rock nearer the surface
…which makes it more geologically active
Comparing the Planets
Which planets have the most and least
geological activity?
Planetary magnetic fields
Moving charged particles create magnetic fields.
So can a planet’s core if it is electrically conducting,
convecting, and rotating
Earth’s Magnetosphere
Earth’s magnetic fields protects us from
charged particles from the Sun
The charged particles can create aurorae
(“Northern lights”)
How do we know what is inside
the Earth?
A. We can drill deep inside the Earth.
B. We can use optical fibers to see deep
inside the Earth.
C. X-ray machines allow us to view the
inside of the Earth.
D. Seismic waves generated by earthquakes
probe the Earth’s interior.
How do we know what is inside
the Earth?
A. We can drill deep inside the Earth.
B. We can use optical fibers to see deep
inside the Earth.
C. X-ray machines allow us to view the
inside of the Earth.
D. Seismic waves generated by
earthquakes probe the Earth’s interior.
What processes shape Earth’s
surface?
What processes shape Earth’s
surface?
1)
2)
3)
4)
Impact cratering
Volcanism
Tectonics
Erosion
Impact Cratering
Impact Cratering
• Moon must be hit as
often as Earth.
• Where are Earth’s
craters?
• Erased by tectonic
activity and erosion.
The more craters, the
older the surface
Volcanism
Molten rock rises when
it is:
• Less dense than its
surroundings.
• Squeezed by its
surroundings.
• Pushed by expanding
trapped gas (water
vapor, CO2, N2, H2S,
SO2)
Volcanism
• Erases other geologic features
• Provides gas for our atmosphere
• Provides water for our oceans
Why doesn’t Mars have as much
volcanic activity as Earth?
A. It’s too far from the Sun, so it cooled off
faster.
B. It’s smaller than the Earth, so it cooled off
faster.
C. It might, we just haven’t seen them erupt
yet.
Why doesn’t Mars have as much
volcanic activity as Earth?
A. It’s too far from the Sun, so it cooled off
faster.
B. It’s smaller than the Earth, so it cooled
off faster.
C. It might, we just haven’t seen them erupt
yet.
Tectonics and Plate Tectonics
Tectonics: any surface reshaping from forces
on the lithosphere
Internal Heat Required!
Plate tectonics: pieces of lithosphere moving
around on mantle
Responsible for mountains, earthquakes,
volcanoes
Only Earth has plate tectonics.
Erosion
• Wearing down of geologic features by wind, water and
ice (weather)
• Important on Earth - why?
How does Earth’s atmosphere
affect the planet ?
How does Earth’s atmosphere
affect Earth?
1) Erosion
2) Protection from radiation
3) Changes the surface temperature:
greenhouse effect
4) Allows the existence of liquid water at the
surface
Radiation Protection
• X-ray light absorbed
very high in the
atmosphere.
• Ultraviolet light
absorbed by ozone
(O3)
The Greenhouse Effect
How does the greenhouse effect
alter surface temperature?
Earth’s atmosphere absorbs light at most wavelengths.
Greenhouse
effect:
Certain
molecules let
sunlight through
but trap escaping
infrared photons
(H2O, CO2, CH4)
A Greenhouse Gas
• Any gas that absorbs infrared
• Greenhouse gas: molecules with 2 different types
of elements (CO2, H2O, CH4)
• Not a greenhouse gas: molecules with single or 2
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.
What have we learned?
• Why is Earth geologically
active?
• Internal heat drives geological
activity, and Earth retains
plenty of internal heat because
of its relatively large size for a
terrestrial world. This heat
causes mantle convection and
keeps Earth’s lithosphere thin,
ensuring active surface
geology. It also keeps part of
Earth’s core melted, and the
circulation of this molten metal
creates Earth’s magnetic field.
What have we learned?
• What processes shape Earth’s surface?
• The four major geological processes are
impact cratering, volcanism, tectonics, and
erosion. Earth has experienced many
impacts, but most craters have been erased
by other processes. We owe the existence of
our atmosphere and oceans to volcanic
outgassing. A special brand of tectonics—
plate tectonics—shapes much of Earth’s
surface. Ice, water, and wind drive rampant
erosion on our planet.
What have we learned?
• How does Earth’s atmosphere affect the
planet?
• Two crucial effects are (1) protecting the
surface from dangerous solar radiation—
ultraviolet is absorbed by ozone and X rays
are absorbed high in the atmosphere— and
(2) the greenhouse effect, without which the
surface temperature would be below freezing.