The Earth / Moon System



Easiest to study?

Still highly speculative!!

Start here & use Earth as a baseline for the other planets

Personal stats

Get from Appendix 9 & 10

Mass 8.2 X 10^23 grams (9 X 10^17 tons)

The moon

Actually relatively large compared to the size of the earth

An active planet

Apparent from volcanic activity

Must be internal forces still at work

Tough to study

Earthquake waves

Internal Structure - on overhead



Tied to internal structure

Zoned by density

Obviously still quite warm inside

Lots of volcanic activity

Plate tectonics - Describe in general terms

Has a strong magnetic field

Due to dynamo effect from inner/outer core


Original atmosphere probably gone

Blown away by solar wind

What we have has been produced since the earth's formation

Volcanic and biologic processes, also comets


Probably the most distinguishing characteristic

Origin - Volcanic and comets

Makes life possible - Can we imagine life without water?




Density only 3.2 - same as basalt

No iron/nickel core?

Origin of moon?

Chunk of the earth's surface?

No water or other volatiles evident

All lost early in lunar history

Interior - silicates all the way through?

Apparently no volcanism or tectonics of any kind

Small quakes associated with impacts

Little or no heat flow - Basically dead

The surface


Oldest part of the exposed lunar crust

Heavily cratered due to the accumulation of debris

Age of rock from the highlands 4.2 to 4.4 b.y.

Lunar "seas" or marias

Dark plains - covered with basalt (like earth's oceanic crust)

3.3 to 3.8 b.y. old

Most roughly circular in shape - clearly fill impact scars

All volcanic activity apparently stopped 3.3 b.y.a. - geologically dead!

Mountains - From impacts

Surface processes

Soil - Dust from impacts

No wind or water to weather or erode the surface

All shaping due to impacts

Geologic summary

Major bombardment phase - ended 4 b.y.a. w/ 6 or so major impacts (100s of kilometers across)

Volcanically active for another billion years - Created the "maria"

Flood basalt only - no volcanic mountains

Dead for the last 3 billion years

Apparently no volcanism or tectonics of any kind

Small "moonquakes" associated with impacts