Planetary surfaces share some similar features, but not all.
Impact craters
Volcanoes and lava flowsErosional features
Uplifted mountains
Rift valleys
Examples of geological surface features:
Terrestrial planet interiors have similar layers
All terrestrial planet interiors underwent “differentiation”
How do we know what’s inside the Earth? Have we been there?
NO! Seismic waves are our probes of the Earth’s interior
Seismic waves
P waves: “primary”, “pressure”, or “push-pull”
S waves: “secondary”, “shear”, or “side-to-side”
P waves can penetrate the liquid outer core
S waves can’t
This science is called “seismology”
The waves bend as they move through changing densities
Which is the densest layer of the Earth’s interior?
A) Crust
B) Lithosphere
C) Mantle
D) Liquid core
E) Solid core
What causes geological activity?
HEAT
So where does the heat come from?
Accretion
Impacts bring kinetic energy
Differentiation
Gravitational potential energy is released as denser material sinks
Radioactive decay
Still heating the Earth’s interior today
How do planets lose that heat?
Radiation
Convection
Conduction
When a planet has lost too much heat, it loses its geological activity:
Volcanoes
Plate tectonics
Earthquakes
Large planets stay warm longer:
• More heat to begin with
• Smaller surface area to volume ratio
3 ways:
Note that convection can carry heat all the way out through the crust in the form of volcanoes
Magnetic Fields
Bar magnet –
field created by orbiting electrons
Electromagnet –
field created by electrical current
Earth’s magnetic field –
created by convection in molten core and Earth’s rotation
Magnetic field also depends on internal heat
All magnetic fields are created by moving charges
Volcanism
Wind erosion Impact cratering
Water erosion
Glacial erosion
Plate tectonics
Shaping planetary surfaces
Impact Cratering
The explosion is caused by energy
released (vaporizing the rock), like a bomb going off
The underlying crust is fractured
Ejecta is thrown out and may create
“secondary craters…”
Typical features in larger craters:• Central peak (rebound)
• Terraced walls
These features erode over time
Only relatively young craters retain those features
Theophilus
Cyrillus
Catharina
Fracastorius
Mare Nectaris
Rosse
Madler
Rank the craters, oldest to youngest.
A) Ptolemy, Alphonsus, Arzachel
B) Ptolemy, Arzachel, Alphonsus
C) Arzachel, Alphonsus, Ptolemy
D) Arzachel, Ptolemy, Alphonsus
E) Alphonsus, Ptolemy, Arzachel
Alphonsus
Ptolemy
Arzachel
Volcanism
Low viscosity
Maria
Medium viscosity
Shield volcanoes
High viscosity
Stratovolcanoes
Silica content determines viscosity
Oceanic crust: Denser, sinks below continental
Continental crust: Less dense, rides above oceanic
Mid-ocean ridge: New crust is forming here
Subduction: Where oceanic crust sinks below continental
Rift zone: Where continental plate is being pulled apart
Plate tectonics
Which process formed the geological feature shown?
A) Impact cratering
B) Water erosion
C) Volcanism
D) Tectonics
E) Glacial erosion
Which process formed the geological feature shown?
A) Impact cratering
B) Water erosion
C) Volcanism
D) Tectonics
E) Glacial erosion
You can tell the relative age of surfaces by looking at the number of impact craters
Few craters = relatively young
(3.0 – 3.9 billion years)
Lots of craters = relatively old
(4.4 billion years)