Geology Reference
In-Depth Information
represented in samples from the Apollo 17 mission, the
Luna 20 site, and possibly from the Apollo 16 site. Other
large basins formed during the Nectarian Period include
Crisium and Humorum. High-aluminum mare lavas and
lavas rich in KREEP components were erupted at this time
as well.
The Imbrian Period began with the formation of the
Imbrium basin at ~3.85 Ga and the emplacement of its ejecta,
the Fra Mauro Formation. The Orientale basin, formed dur-
ing this time, marked the cessation of large impacts on the
Moon (and probably the inner Solar System in general). This
period of time saw extensive eruptions of mare basalts,
flooding the
floors of near side basins and embaying heavily
cratered highland terrains. Mapping the relative ages of mare
materials in accord with this system shows that lunar volcan-
ism began at ~3.9 to 4 Ga to ~1.2 Ga, with most eruptions
occurring in the late Imbrian Period.
The Eratosthenian and Copernican Periods were origi-
nally based on mapping and relative ages of crater depos-
its from the impact craters Eratosthenes and Copernicus.
Eratosthenian-age craters are
“
fresh,
”
with sharp crater
rims and clearly identi
ed secondary craters, although
lacking bright rays, while Copernican-age craters are suf-
ficiently young to still show bright rays (
Fig. 4.8
).
Assignments
1.
Compare and contrast the Apollo lunar landing sites
with those of the former Soviet Union; be speci
c with
regard to the type(s) of terrain (mare, highland, etc.)
and the key scienti
c objectives.
4.
Explain the concept behind the discovery of lunar
mascons.
5.
Compare the
figures showing the distribution of lunar
maria with the diagram for the interior of the Moon
and offer an explanation for why maria are concen-
trated on the near side.
2.
Refer to
Chapter 3
and the relations of the morphology of
volcanic features; consider lunar maria, lunar volcanic
domes, and lunar sinuous rilles and infer the key param-
eters (composition, rate of effusion, etc.) involved in their
formation, taking into account the lunar environment.
6.
Discuss how water-ice can be present on and near the
surface of the Moon.
3.
Discuss what might be expected in ejecta deposits
found in a lunar mare setting 500 km from the source
impact crater in the lunar highlands.
