NEEP602 Lecture #10

NEEP602 Course Notes (Fall 1996)
Resources from Space

Lecture #10: What does the Moon tell us about the Earth?

Evolution of the Moon: The Apollo Model

Visuals

Slides illustrating the phases of lunar evolution and providing reconstructions of various periods.

Notes

Before Apollo 11, we knew a lot about the relative sequence of major events in lunar history but not the span of time each represented.

Pre-Apollo Model for Lunar Evolution

After the analysis of Apollo 17 data, we now had significant knowledge about the absolute ages of the stages of lunar evolution as well as details of events and processes about which we had never dreamed.

Apollo Model: Stages of Lunar Evolution

Stage One: The Beginning - 4.55 eons. The Moon formed contemporaneously with the Earth.

Major Issue: Did the Moon form by fission of the Earth or by capture by the Earth (Hartmann, 1986 and Alfven and Arrhenius, 1972)?

Major Issue: Once formed, to what extent did the Earth and the Moon follow similar courses of geologic evolution?

Major Issue: What insight does the evolution of the Moon give us about the conditions on Earth as life began and evolved?

Stage Two: The Magma Ocean - 4.5-4.4(?) eons. Accretionary melting, volatile depletion due to high temperatures and low gravity, and crystal settling and floating differentiated the outer 400-500 km of the Moon.

Major Lunar Features: End of the Magma Ocean Stage
A dunite (predominently olivine) fragment in an impact breccia. The oldest rock sampled by Apollo astronauts - about 4.6 billion years old.

Stage Three: The Cratered Highlands - 4.4(?)-4.2(?) eons. Impacts of comets, asteroids, and other debris, capable of forming craters at least 50 km in diameter, saturated the lunar crust once it was capable of supporting itself over the residual magma ocean.

Note: Oldest identified Earth crust is more than 4.0 eons old.

Changes to Lunar Features: End of the Cratered Highlands Stage
Mapping Camera 1566: Typical farside cratered highlands
Typical farside cratered highlands

Stage Four: The Old Large Basins/Crustal Strengthening - 4.2(?)-3.9 eons. Large impact basins formed, but rapid crustal adjustment occurred followed by strengthening of that crust, possibly due to residual liquids (KREEP) from the crystallization of the magma ocean moving into the crust and crystallizing.

Changes to Lunar Features: End of The Old Large Basins/Crustal Strengthening Stage
Full Moon showing eastern limb basins

Stage Five: The Young Large Basins - 3.9-3.8 eons. Additional large impact basins formed, but the crust was strong enough to support mass concentrations and deficiencies indefinitely.

Major Issue: Cataclysm at 3.9 eons or not.

Changes to Major Lunar Features: End of the Young Large Basin Stage
Mapping Camera 1578: View of Tsiolkovskiy
Mapping Camera 2797: View of Tsiolkovskiy
Boulder made up of impact generated breccia.
Contact between two impact breccia units in boulder.
Older, blue-gray impact breccia unit.
Sample of blue-gray impact breccia.
Sample of anothosite fragment from blue-gray unit.
Younger, vesicular impact breccia unit.
Sample of vesicular impact breccia.
Injection veins of glassy impact breccia in breccia.

Text

Evolution of the Moon: The Apollo Model

Originally published by the author in American Mineralogist, v 76, 773-784.

Questions

1. What is the best evidence that the Moon was not pulled from the Earth (leaving the Pacific Ocean Basin in its wake) since life evolved on the Earth? Explain.

2. What explanation(s) can you give for the concentration of ages of samples of lunar impact breccias around 3.9 eons other than a cataclysm at that time?

3. Give a geophysical explanation for the mass concentrations (mascons) and mass deficencies in and around young large basins on the Moon and what conditions are necessary for them to persist for almost 4.0 billion years. Contrast with the Earth.

References

Alfven, H., and Arrhenius, G., 1972, Origin and Evolution of the Earth-Moon System, The Moon, v 5, 210-230.

Cooper, H.S.F., 1970, Moon Rocks, Dial, New York, 197p.

Head, J.W., et al, 1993, Lunar Impact Basins: New Data for the Western Limb and Far Side (Orientale and South Pole-Aitken Basins) from the First Galileo Flyby, Journal of Geophysical Research, v 98, 17149-17181.

Hartmann, W.H., 1986, Origin of the Moon, Lunar and Planetary Institute, Houston.

LPI, 1988, Workshop on Moon in Transition: Apollo 14, KREEP, and Evolved Lunar Rocks, LPI Technical Report Number 89-03,156p.

LPI, 1992, Workshop on the Physics and Chemistry of Magma Oceans from 1 Bar to 4 Mbar, LPI Technical Report Number 92-03, 79p.

Shoemaker, E.M., 1962, Interpretation of lunar craters, in Zdenek Kopal, editor, Physics and astronomy of the Moon, P. 283-359, Academic Press, New York.

Taylor, S.R., 1982, Planetary Science: A Lunar Perspective, Lunar and Planetary Institute, Houston, 481p.

Wilhelms, D. E., 1987, The Geologic History of the Moon, U.S. Geological Survey Professional Paper 1348, U.S. Government Printing Office, Washington, 302p.

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Lecture #10: What does the Moon tell us about the Earth?