NEEP602 Course Notes (Fall 1996)
Resources from Space

Lecture #11: What does the Moon tell us about our future!

Title: Evolution of the Moon: The Apollo Model, continued


Slides illustrating the phases of lunar evolution


Geologic Map of the Lunar Nearside (Upper Imbrian System) (Wilhelms, 1987) [277 kB]
Geologic Map of the Lunar Farside (Upper Imbrian System (Wilhelms, 1987) [233 kB]

Cratering on the Moon: A dominating process! Most impact velocities are between 15 and 20 km/sec, giving associated pressures of several hundred GPa and extraordinary amounts of heat as conversion of kenetic energy into forward and rearward shock waves takes place almost instantaneously. Most of the projectile is melted, vaporized, or ionized.

<10 m diameter craters (transition up to 100 m diameter)
o normally do not penetrate regolith
o depth to diameter ratio variable
o glass-lined pits in center of fresh craters
o deep pits in the center of some craters
o inner benches common
o impact breccias present in and outside larger craters
<10 km diameter craters (transition up to 30 km diameter)
o normally penetrate regolith
o hemispherical hole with raised rim
o depth to diameter ratio 1:3 to 1:4
o ejecta blankets extend to about one crater diameter
o target strata overturned but preserved in ejecta blanket
o inner benches and impact breccias associated with smaller craters
<100 km diameter craters
o flat floors with central mound or peak
o slumped (landslide) benches on walls
o indications of pools and flows of impact melt
o ejecta blankets extend to about one crater diameter
o target strata overturned but preserved in ejecta blanket
o secondary impact craters, crater clusters, and crater chains extent many crater diameters
>100 km diameter basins
o generally flat, fractured floors with partial of complete inner rings of peaks
o slumped (landslide) benches on walls
o extensive pools and flows of impact melt inside and outside the primary impact crater rim
o ejecta blankets extend many crater diameters with evidence of significant lateral flow (do lithostatic pressures become a factor?)
o one to six rings of mountains outside primary impact crater rim (multiring basins generally >400 km in diameter)

Lunar Evolution: The Apollo Model
Major Lunar Features: End of the Young Large Basin Stage

Note: Lunar wide, light-colored debris deposits in closed basins, whose deposition appears to post-date the large basins, may have several origins, including gas-charged impact debris and gas-charged precursors to eruptions of mare basalt that entrained light-colored crustal debris.

Stage Six: The Basaltic Maria - 3.8-3.0(?) eons. Mare basalt, including pyroclastic debris from late fire fountains, erupted at the lunar surface and intruded the subsurface.

Note: The Earth continues to evolve toward compositional, thermal, and gravitational equilibrium due to convection, melting, and differentiation (Bowring and Housh, 1995). The influence of such processes on the Moon was much more limited and largely concluded with the end of the Basaltic Maria period, about 3.0 eons ago, although there is some evidence of continuing local mare basalt eruptions in the Procellarum region.

Major Lunar Features: End of the Basaltic Maria Stage
Full Moon albedo variations
Map of Nearside Maria (Wilhelms, 1987) [250 kB]
Mare Imbrium surface structures at sunrise from 60 nm.
Taurus-Littrow Mare from 60 nm.
Boulder field around Camelot crater at Taurus-Littrow.
Mare basalt boulder in situ at Taurus-Littrow.
Vesicular basalt from Taurus-Littrow.
Non vesicular basalt from Taurus-Littrow.
Orange soil deposit in rim Shorty crater.
Shorty Crater, about 80m in diameter.
Orange soil deposits in the Sulpicious Galles region on the southern rim of Serenitatis.

Stage Seven: The Mature Surface - 3.0(?) to present. Formation of rayed impact craters and the regolith continued in all regions and included the implantation of solar wind gases in the regolith materials.

Light-colored swirls of unknown origin have formed on, and possibly in, the regolith, particularly in regions east of Smythii.

Changes to Major Lunar Features: Mature Surface Stage

Regolith: " a terrestrial term, also used for the Moon. It has been defined as 'a general term for the layer or mantle of fragmental and unconsolidated rock material, whether residual or transported and of highly varied character, that nearly everywhere forms the surface of the land and overlies or covers bedrock. It includes rock debris of all kinds, including volcanic ash .. '... lunar regolith consists of particles <1 cm in size although larger cobbles and boulders, some as much as several meters across, are commonly found at the surface....much of the pulverized material is melted and welded together to produce breccias (fragmental rocks) and impact melt rocks, which make up a significant portion of the regolith ..." (Heiken, et al, 1991) Shoemaker, et al., 1968, is a particularly important reference in regard to characterization of the lunar regolith.
A particularly important part of the lunar regolith consists of aggregates of rock, mineral, and glass fragments, held together by impact melt glass, called agglutinates. Further, the lunar regolith contains adsorbed solar wind gases, meteoritic material, and the products of solar and cosmic radiation.

Pit bottomed crater in th.e regolith.
Incompletely mixed regolith units.
Everyman's Moon: Geophysical Constraints
A schematic cross section of the Moon as it probably exists today


1. What are the arguments, pro and con, for an origin of the Moon through the "great Mars-sized asteroid impact on the Earth theory" (fission)? (Start with Hartmann, 1986, and Alfven, H, and Arrhenius, G, 1972, in Lecture #10, but later refinements by both should be sought in the literature.)

2. What might be the implications of the events of Stages Two through Seven of lunar evolution on the evolution of life on Earth? (See the text for Lectures #10 and 11 as a start.)

3. List six major scientific issues yet to be resolved about the evolution of the Moon other than its Beginning.


Evolution of the Moon: The Apollo Model (continued)

Based on material originally published by the author in American Mineralogist, v 76, 773-784.

References (see Lecture #10)

Bowring, S.A., and Housh, Todd, 1995, The Earth's Early Evolution. Science, v 269, 1535-1540.

Shoemaker, E.M., et al, 1968, Television observations from Surveyor , In Surveyor Project Final Report, Part II, JPL Technical Report 32-1265, NASA SP-146, p 21-136.

Williams, D.A., et al, 1995, Multispectral studies of western limb and farside maria from Galileo Earth-Moon Encounter 1, Journal of Geophysical research, v 100, 23291-23299.

Heiken, G., et al, 1991, Lunar Source Book, Cambridge University Press, Cambridge.

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