1. Terrestrial Planetary Geology: Basic Processes & Earth

2. What are terrestrial planets like on the inside?
Planets (inc. Moon) to scale, with typical surface features

3. Earth’s Interior Core: Highest density; nickel and iron
Mantle: Moderate density; silicon, oxygen, etc.
Crust: Lowest density; granite, basalt, etc.
Other terrestrial planets have similar layers

4. Terrestrial Planet Interiors
Applying what we have learned about Earth’s interior to other planets tells us what their interiors are probably like

5. Differentiation Gravity pulls high-density material to center
Lower-density material rises to surface
Material ends up separated by density
This generates heat inside planet

6. Lithosphere
A planet’s outer layer of cool, rigid rock is called the lithosphere: crust + outer mantle
It “floats” on the warmer, softer rock that lies beneath: most of the mantle is “plastic”-- the rock slowly deforms

7. Strength of Rock
Rock stretches when pulled slowly but breaks when pulled rapidly--like Silly Putty but MUCH slower
The gravity of a large world pulls slowly on its rocky content, shaping the world into a sphere if bigger than about 300 km in diameter
Rapid shear, like an earthquake or impact breaks rock

8. Seismic Waves Let Us Know What’s Inside a Planet
P (primary) waves push matter back and forth (longitudinal like sound waves)
S (secondary) waves shake matter side to side (transverse, like water waves)

9. SEISMIC WAVES REVEAL INTERIOR
SEISMOGRAPHS detect EARTHQUAKES, VOLCANOS, and EXPLOSIONS at varied distances.
Long surface (L) waves travel fastest, but are not very useful as they don't probe the interior.
P-waves, PRIMARY, (push-pull waves) are COMPRESSIONAL, LONGITUDINAL waves. Propagate through liquids as well as solids VP = function of (compressibility; composition, T, P)
S-waves, SECONDARY, (side-slip) are SHEAR, TRANSVERSE waves. CANNOT propagate through liquids (OUTER core). VS = (a new) function of (rigidity; composition, T, P)
We have some seismic measurements for the Moon too: seismometers left by Apollo astronauts

10. Seismic Wave Paths
Both S and P waves can be detected from earthquakes on the same side of the earth,
ONLY P waves are detected on the opposite side of the earth
“shadow zone”: region where no S (absorbed) & only weak P (refracted) waves are detected.
Tells us the outer core of the earth is LIQUID

11. Seismographic measurements have found for Earth
Boundaries between: inner/outer core; outer core/mantle; composition changes in mantle (600 km); oil and natural gas deposits in crust.
Seismic measurements can even detect excess rotation of earth’s inner core, upwellings and sideways motions in the mantle.
MODERN SEISMOLOGY CAN GIVE A 3-D PICTURE, CHANGING IN TIME, OF THE EARTH'S INTERIOR! Tomography
There is a good analogy with 3-D images of people's interiors from MRI or CAT scans.

12. Thought Question
What is necessary for differentiation to occur in a planet?
a) It must have metal and rock in it
b) It must be a mix of materials of different density
c) Material inside must be able to flow
d) All of the above
e) b and c

13. Thought Question
What is necessary for differentiation to occur in a planet?
a) It must have metal and rock in it
b) It must be a mix of materials of different density
c) Material inside must be able to flow
d) All of the above
e) b and c