NEEP602 Course Notes (Fall 1997)
Resources from Space

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

Evolution of the Moon: The Apollo Model


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


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 mission 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 - 4.56-4.57 eons. The Moon formed contemporaneously with the Earth.

  • Major Issue: Did the Earth and Moon and the other terrestrial planets form directly from the condensing solar nebula or was there an intermediate step of planetesimal formation?
  • Initial condensation as well as planetesimal growth would be the result of a slight tendency of particles to stick together after collisions.
  • According to modeling studies (D.N.C. Lin as reported by Peterson, 1993), this would be followed by "runaway" aggregation as gravitational forces began to play a larger and larger role?
  • Major Issue: Did the Moon form by impact induced fission of the Earth or by capture of a nearly co-orbiting small planet by the Earth (Hartmann, 1986 and Alfven and Arrhenius, 1972)?
  • Modeling simulations suggest that the collision of a Mars-sized asteroid with an early, differentiated Earth could have ejected debris that would have coalesced to form the early Moon.
  • Planetary capture of natural satellites has occurred frequently as shown by six satellites in the solar system that are in retrograde orbits. This origin is supported by the following arguments:
  • "Runaway" accretion of the Moon and other terrestrial planets from smaller planetesimals would result in a cool, initially undifferentiated interior with temperatures increasing outwardly as the energy of accretion increased.
  • An initially and still relatively cool interior of the Moon is supported by 1) primordial elemental and isotopic compositions associated with volcanic materials of deep-seated origin and 2) trace element systematics in lunar rocks that are not consistent with earlier differentiation as part of the Earth (----)
  • Strong evidence that only about the outer 500 km of the Moon was molten and fully differentiated (see Magma Ocean discussion below).
  • Major Issue: Once formed, to what extent did the Earth, Moon, and other terrestrial planets follow similar courses of geologic evolution?
  • Initial differentiation of sufficiently heated outer portions of the terrestrial planets and the Moon probably followed similar courses, including formation of a calcium-rich crust over a magnesium and iron-rich mantle with the protocore formed by the migration of immiscible iron-sulfur liquid to the center of the planet (see Stage Two, below).
  • Planets as large as the Earth and Venus continued to differentiate as radioisotopic heat, in excess of that that could be transferred to the surface by conduction, induced internal convection which recycled the early crust and mantle (plate tectonics) and continually modified the chemical composition of each and of the core .
  • Geochemical evidence from the oldest crustal rocks on Earth (4.0 billion year old and younger Archean rocks) indicates that such recycling began very early (Bowing and Housh, 1995).
  • Recycling of the crusts and mantles of the Moon and Mercury have not occurred due to the absence of significant thermal convection and plate tectonics.
  • Some recoiling of Martian crust and mantle has been proposed on the basis of early Pathfinder data

  • Stage Two: The Magma Ocean - 4.5-4.4(?) eons. Accretionary melting, due to conversion of kinetic energy to heat and to the decay of short lived radioisotopes (e.g. 26Al), 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

    Differentiation of the Lunar Magna Ocean by Crystallization.

     A dunite (predominently olivine) fragment in an impact breccia
    The oldest rock sampled by Apollo astronauts - about 4.6 +/-0.1 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 surface of the lunar crust once it was capable of supporting itself over the residual liquids of the magma ocean.





     Changes to Lunar Features: End of the Cratered Highlands Stage

     Mapping Camera 1566: Typical farside cratered highlands

     Typical farside cratered highlands
  • Major Issue: What process or processes produced the light plains materials that partially fill pre-Mare Basalt (Stage Six) basins?
    • Hot and gas mobilized flows of fine impact debris radiating from Large Basin forming impact events (Stages Four and Five)?
    • Pre-Mare Basalt (Stage Six) eruptions of gas mobilized initial partial melting components of the mantle with intrained crustal debris?

  • Stage Four: The Old Large Basins/Crustal Strengthening - 4.2(?)-3.9 eons. The Old Large Basins/Crustal Strengthening - 4.2(?)-3.9 eons. More than 30 large impact basins formed, but rapid crustal adjustment occurred followed by strengthening of that crust. This strengthening was possibly due to potassium, rare earth elements, and phosphorous-rich residual liquids (urKREEP) left over from the crystallization of the magma ocean, moving from the mantle-crust boundary, a strengthening process in and of itself, and into the crust and crystallizing into interlocking dikes within the myriad of crustal fractures.





    Changes to Lunar Features: End of The Old Large Basins/Crustal Strengthening Stage 

    Full Moon showing eastern limb basins

    Topographic map of the South Pole-Aitken Basin area based on Clementine data. The basin is about 2500 km in diameter and the largest of the Old Large Basins

    Stage Five: The Young Large Basins - 3.9-3.8 eons. An additional 8 large impact basins formed, but the crust was strong enough to support mass concentrations and deficiencies indefinitely.

    Changes to Major Lunar Features: End of the Young Large Basin Stage
    Mass concentrations in and mass deficiencies around Young Large Basins as shown by Bouguer gravity anomalies derived from global topography and free-air gravity models based on Clementine data (Nozette, et al., 1994, p.1841)



    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 anothrosite fragment from blue-gray unit
    Younger, vesicular impact breccia unit
    Sample of vesicular impact breccia
    Injection veins of glassy impact breccia in breccia


     Clementine Topographic Map of the Moon showing the distribution of lunar basins (see figure 1 at )
    Figure: Map of Nearside Young Large Basins (Nectarian System) (Wilhelms, 1987)
    Figure: Map of Farside Young Large Basins (Nectarian System) (Wilhelms, 1987)
    Figure: Map of Nearside Young Large Basins (Lower Imbrian System) (Wilhelms, 1987)
    Figure: Map of Farside Young Large Basins (Lower Imbrian System) (Wilhelms, 1987)
    Figure: Map of Nearside Young Large Basins (Upper Imbrian System) (Wilhelms, 1987)
    Figure: Map of Farside Young Large Basins (Upper Imbrian System) (Wilhelms, 1987)

    Evolution of the Moon: The Apollo Model

    Originally published by the author in American Mineralogist, v 76, 773-784, 1991.


    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.


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

    Bowring, S.A., and Housh, T., 1005, The Earth's Early Evolution, Science, 269, 1535-1540.

    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.

    Mojzsis, S.J.., et al, 1996, Nature, November 7

    Nozette, S., et al, 1994, The Clementine Mission to the Moon, Science, 266, 1835-1862.

    Peterson, I, 1993, A Rocky Start, Science News, 143, 190-191

    Schopf, J.W., 1993, Science 260, 640.

    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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