Common Donor - Capture Theory of Moon Origin

Questions this theory answers.

See the movies:

  1. Solar System Introduction
  2. Solar System Origin Outline
  3. Moon Origin


Ever since the Apollo Astronauts brought back rocks from the moon, speculation about that body’s origin has been rife. On first appearances, the moon rocks laid to rest earlier theories such as simultaneous coeval formation — the earth as the ‘brother’ of the moon; the fission hypothesis — the earth as the ‘parent’ of the moon; and the capture hypothesis in which the earth is the ‘foster parent’ of the moon. A theory that has subsequently gained credence is a compromise of these three - the Earth Impact Theory. Under this model an impactor the size of Mars or larger strikes the earth and fragments or vaporises, and the bulk of the moon forms from the remains of the impactor. However this compromise theory struggles to account for common rock chemistry of the earth and moon, and the mechanics of this theory continue to encounter some difficulty.

Of the discarded theories, the capture hypothesis suddenly comes back into contention if the chemical evidence of common moon and earth rock origin can be shown to be harmonious with the introduction hypothesis and the mechanics of the introduction can be explained.

The mechanical problem: To introduce a body the size of our satellite into its present orbit without destroying it and devastating the surface of the earth through repeated close encounters. To do so would be an extremely sophisticated and unlikely procedure.

The chemical problem: The chemistry of (sampled) rocks of Earth and Moon is similar, yet it is different. A chemical similarity is found in factors such as a unifying mathematical relationship of oxygen isotopes — indicative of some sort of syn-genesis. Differences centre on the moon’s relative depletion in iron and some volatile substances — as though the moon rocks are a lighter, dryer product of a differentiating process which left heavier and more volatile elements as the earth's portion.

Consider yourself in the position of the designer of a life-supporting planetary system.

On one planet — the planet third from the sun — you have chosen to place life. In pursuit of your plan for life, and a suitable planet for it, you have calculated the need for a satellite or moon of a certain size and mass, needed from a specific time onwards in history. This time will be relatively late in geologic history. Your moon will not be required until immediately preceding the advent of complex organisms. This means that for at the very least four-fifths of the history of the planet, the moon is not needed. Placing it into orbit around the earth from the earliest times would slow the earth’s spin and necessitate various major orbital re-adjustments from time to time. Yet the best time to form the moon is back in time, when the planets are younger. You have a moon, but you do not need it in its final location as yet. What do you do with it?

You store it somewhere.

Where do you store it?

You logically store it at or near its place of origin, and in a place from which its final "owner" can "collect" it.

What is the moon’s place of origin?

It has been built to size and weight. It is exceptional among the stony planets for being large for its mass. It is built from rock, with very little heavy metallic core. Being mostly rock, it is of similar composition to the rock mantle which overlies the metal cores of the stony planets. Mercury, the body currently closest to the sun, is missing a quantity of its mantle. Whether this was the source of the moon, or whether another planet even closer to the centre of the solar system was divided up for the purpose, the end result is the same. The moon almost certainly came from near the centre of our planetary wheel, at a time of upheaval. Heat and disturbance logically had the effect of making nearby bodies ready to shed parts of themselves.

You have made the moon to specifications. You need now to store it and transport it to its final site — at the desired time. It seems probable you will bring something with it, or arrange for it to gain it during arrival — an atmosphere. This atmosphere will gradually fret away under the force of the sun’s radiation and the earth’s superior gravitational attraction, and will thus be a standing supply of essential re-supply compounds for the earth’s atmosphere. As the yet-to-be-revealed trees and the complex forms of life draw essential compounds out of the atmosphere and waters, and tie them into the earth as limestones, fossil fuels, and so on, you will re-supply these compounds by a steady stream from the newly-positioned moon. The element which will by far be the most heavily drawn upon will be carbon, so you arrange for the moon to be coated in a rich supply of carbon dioxide — either bringing it with itself from its storage site, or gaining it en route or soon after arrival. This could be achieved by encasing it in a sizeable dry-ice-rich comet. This supply will fully deplete at a time allowing carbon dioxide levels in the earth’s atmosphere to deplete to crisis levels — just as industry begins to re-supply this compound by burning the fossil fuels. (Life on earth had just a few centuries remaining when man began to re-supply the atmosphere with this vital compound. (Krauskopf, 1967, p 600-630))

You have manufactured a suitable body of rock, shaped it, begun to mark its surface to make it an excellent all-over reflector, and stored it for the duration. Where did you store it?

The planetary sequence outwards from the centre of the solar system is: Mercury, at or near the probable source of the moon; Venus (the Morning Star); and Earth. Of all the planets, these three have their orbits closest each other’s, and are the most logical "stairway" out which the moon could have travelled. Tie the moon as loosely as is feasible to one of these, and allow the next planet out from it to swerve in towards it, or perhaps utilize a propelling impact on the moon at the propitious moment — and, transfer! It could be done, although mathematicians tell us it would be a sophisticated procedure.

Assume the moon was projected outwards from the region of Mercury and the sun early in history. Assume it resided with Venus for much of earth’s early existence, only being captured by our planet relatively late in geologic time. What evidence exists of prolonged association between Venus (the Morning Star, next closest the sun to us) and the moon? Venus is only a little smaller than the earth, and therefore able to control a moon-sized satellite. As we have learned, it is a step on the stairway between the moon’s probable origin and its destiny. Prolonged association with a body the size of the moon should have greatly reduced Venus’s spin-rate. Venus has almost zero rate of spin. The moon causes tides and some movement and heating effects within the earth itself. It should have had some effect on the history of Venus. At a time which could have been co-incident with a pivotal change in the earth’s geologic history, Venus’s crust and interior appears to have gone dead (Taylor, 1998, p132-3). Apart from a few impact craters, nothing has happened to Venus’s rocks for a long time — while the history of the earth is the reverse. This could also be reflected by magnetic activity. The "Morning Star" has no magnetic field. If it ever did have one, it was so weak or so long defunct that its "ghost" cannot be detected as yet by man-made instruments. The nearby earth, of only approximately one-fifth more mass, has magnetism. This magnetism is yet another essential of the modern world, and could well be a product of tide-like stresses and movements generated deep within the earth. Finally, Venus is shrouded in a thick atmosphere of — carbon dioxide. Whether any of this could have come with the moon — perhaps as dry ice (frozen carbon dioxide) — is problematical: the fact is, the earth has used up approximately six hundred times its current atmospheric reserves of this compound, and its nearest neighbour is coated in it; and this nearest neighbour logically harboured the moon.

You, as engineer of the planetary system, have acted in a logical pattern. You made the moon at a time propitious for such actions: you have kept it at a suitable site; you introduced it precisely when it was required and not a moment before. And so this inspiration of poets and lovers alike makes her stately progress across the sky in a manner at once graceful, and deeply significant for all complex life.

When did she arrive?

If the earth had no large moon for a period of time, then acquired one, the event would be reflected in the rock strata in an unequivocal fashion. The record of it would appear in the geologic strata as a trumpet-blast, as the change between a horse-drawn cart and an automobile. It would stand out universally, it would be in the language of every geologic text.

Is there a trumpet-blast in the rocks, the signal event of all geologic time? Is there a feature in rock-strata which is agreed upon as a sign of a single, contemporaneous event world-wide? An event which generated great turbulence in all but the deepest or most protected waters, and for perhaps tens of millions of years kept most of the world’s sediments from finding permanent rest whilst mountains rose and were cut off, and strata were tilted and folded? From this point in the geologic column upwards, strata and world history would have been profoundly changed in some way. In the system of strata immediately above it, underwater deposits would prevail almost to the exclusion of land deposits; and these water-laid strata could be expected to contain abundant fossils of complex life.

Consult almost any geologic history of the earth and you will find evidence of such an event!

This is the so-called Pre-Cambrian/Cambrian Unconformity, which is the only geologic feature recognizable almost world-wide. It lies at the base of what could perhaps be paraphrased as "The Strata of Ancient Life", or Palaeozoic -- of which the Cambrian System is the lowermost strata-grouping. From this point -- the bottom of the Cambrian -- the familiar geologic column with its shadow of a tree of life within it progresses upwards as though it has really only just begun. (Although simple unicellular life existed for the bulk of the earth’s history, and although there is evidence of a last-minute advance in the complexity of this simple life to a level perhaps equating to structured seaweed, there is every reason to believe that the level of life after this event was an octave above the level of life before the event. Even in places where there is no visible unconformity, there is a revolutionary change in the complexity of life -- which may be discerned in sedimentary rocks by the abrupt appearance of a kaleidoscope of new and advanced fossils.)

Although a relatively few outcrops do not display an unconformity at this level, geology from its early times has recognized the Pre-Cambrian/Cambrian interface as coincident with a subtle and deep-seated change in the environment in which rock strata were deposited. And some have conjectured moon-capture as a possible cause. The event was no more than 550 million years past.

It goes without saying that there were regular tides and some other engines of atmospheric/oceanic movement prior to our moon’s timely debut — but the new arrival injected new meaning into all these processes, and indeed brought something new to the whole earth.

We have strong circumstantial evidence for capture. Do the chemistry and mechanics fit? What if, instead of postulating an earth impact to explain our moon, we postulate a common donor planet supplying materials to both the moon and the earth’s surface?

Mercury, aptly named, is well in front in the race to be the source. It is, almost assuredly, what it is today because of a combination of sloughing and impacts since roughly half of Mercury’s rock mantle is missing. Models of the impacts point to quantities of re-worked stony materials being thrown into the gravitational paths of Venus and Earth. Suppose our moon formed as a sloughing product of a fast-spinning, overheated planet such as Mercury. A subsequent wave of impacts could then have cratered the moon, propelled it into Venus’s influence, and concurrently have stripped materials from Mercury and propelled them towards Earth. Subsequent major cratering of the moon would logically be a product of ice impacts during transport and settling into Earth’s orbit.

One of the most striking features of the earth, not only in comparison with the moon but in comparison with all other explored planets, is the crustal structure of lighter continental rock bodies floating on a heavier substrate. Coupled with this unusual structure of the crust is enrichment by heavy and valuable minerals of the continental land-masses. Our planet has concentrations of metallic elements not only in the core, but also on the surface — highly suggestive of two input events at two different times. Models of the early earth encounter grave difficulties in accounting for these unique compositional features. Some even turn to a rain of Space materials onto the early earth to account for our surface. It seems possible that some other planet, such as Mercury, may have been the source of this material.

The first sloughing/impact event gave rise to the moon: the second, throwing metals-enriched substances towards Earth from deeper in the donor planet, gave rise to a chemical similarity, Earth-Moon.

When our moon finally was delivered, the momentous event was written in the earth as the Pre-Cambrian/Cambrian Unconformity. And the corollary of the Pre-Cambrian/Cambrian event saw Venus pour out her soul in a planet-wide sea of basalt lava, presumably triggered by the upwards pull and perhaps partial impact of a system of massive ice bodies passing in close on their errand of fetching the moon bride. What a train! What a party upon arrival!

Probably only an astronaut could envisage the procedures in docking fast-moving dry-ice buffers onto a planet, and then hurtling effectively a giant comet into earth orbit guided by appropriate impacts from other buffered ice bodies. Mechanics tell us the timing must have been split-second.


The above article has been adapted from the recently published book, ‘The Tree of Life and the Origin of the Species’ published by Daylight Publications, Theodore, Queensland, Australia. The author has drawn his inspiration from two sources: a scientific background as a geologist and the Authorized Version of the Bible.

Further Reading

Beatty, Kelly (2012, March 27). Did the Moon Come From Earth? [Online]. Retrieved April 22, 2012, from Quote, "Zhang and her team find that the Earth-Moon titanium ratios are also matched by aubrite meteorites, now considered the best geochemical match to Mercury's surface."

Brown University (2011, May 26). Scientists detect Earth-equivalent amount of water within the moon. ScienceDaily. Retrieved June 11, 2011, from­ /releases/2011/05/110526141400.htm. Quote, "this new research shows that aspects of this [giant impact] theory must be reevaluated." COMMENT: Hot water held under pressure so that it cannot boil (superheated water), if suddenly released, boils instantaneously and becomes an explosive propellant. This, combined with rapid spin of the donor planet, goes much of the way to explaining how part of a planet's mantle could slough. Substantial water content therefore is compatible with the sloughing proposal. Giant impact demands extreme heat generated by shock which theoretically would eliminate most of the water.

Carnegie Institution (2011, June 17). Mercury: Messenger orbital data confirm theories, reveal surprises. ScienceDaily. Retrieved June 28, 2011, from Quote, "Mercury's surface is not dominated by feldspar-rich rocks. XRS observations have also revealed substantial amounts of sulfur at Mercury's surface, lending support to suggestions from ground-based observations that sulfide minerals are present. This discovery suggests that Mercury's original building blocks may have been less oxidized than those that formed the other terrestrial planets." COMMENT: This suggests that the current surface of Mercury is not the original surface! The feldspar-rich stony material that was expected, could well now be part of the feldspar rich continents here on Earth and of the feldspar bearing parts of the lunar surface. The sulphur is suggestive of the interior of a planet rather than the original surface.

Geoscience News, 29/01/2003, "The only geologist to walk on the moon looks back after 30 years", Published by the Australian Institute of Geoscientists. Quote: "The major problem with [the giant Earth impact] hypothesis," says Schmitt, "is that the . . . lower lunar mantle . . . has a chondritic, that is, primordial elemental and isotopic imprint. This . . . imprint would have disappeared or have been significantly modified if the mantles of the Earth and the impactor had already formed as required by the current giant impact hypothesis." COMMENT: Astro-geologist Schmitt's observations perforce are based on lunar rock samples, meteorite analyses, and on what is known of the mineralogy of the Earth. He opines that the (scant and fragmentary) evidence elicited from such sources suggests that the moon rock samples do not imply the same settling and sorting processes as have occured over time in the earth, but are more akin to supposedly primordial materials such as is found in certain meteorites. (These are the so-called chondritic meteorites). Schmitt's opinion rides comfortably with our Common-Donor Theory, if, say, the minerals of the donor planet had not had time to settle and sort, or, if part of the moon is actually a primordial (i.e. chondritic, after Schmitt's terminology) body, coated with materials from the donor. There is no need to assume that the moon consists entirely of materials from a mantle-sloughing donor.

Goldreich P., 1972, 'Tides and the Earth-Moon System' in Scientific American April 1972, pp. 259-268, Quote: ". . . the one really new hypothesis of lunar origin that has appeared during the past half century . . . was conceived by Gerstenkorn . . . the moon had initially been captured in ... an [highly inclined, eccentric] orbit, and . . . tidal friction had subsequently decreased the orbital eccentricity and inclination . . ."

Lissauer J.J., 25 Sept. 1997, "It's not easy to make the moon", Nature, Vol. 389, pp. 327-328. Quote: "Theory has it that the moon grew within a disk of material splashed out of the Earth by a body the size of Mars. According to new calculations, however, the impacting body was at least twice that size."

NASA (2011, September 29). Orbital observations of Mercury reveal flood lavas, hollows, and unprecedented surface details. ScienceDaily. Retrieved October 1, 2011, from Quote: "These new data rule out most existing models for Mercury's formation that had been developed to explain the unusually high density of the innermost planet, which has a much higher mass fraction of iron metal than Venus, Earth, or Mars, Peplowski pointed out. Overall, Mercury's surface composition is similar to that expected if the planet's bulk composition is broadly similar to that of highly reduced or metal-rich chondritic meteorites (material that is left over from the formation of the solar system)." COMMENT: The model these findings affirm is accretion of Mercury without an ignited sun close by, followed by sloughing of the outer mantle, followed again by massive impact and by partial reconstruction around the remnant iron core. Probably the best chance of observing the original surface of Mercury is to look at our Moon: and parts of Mercury's deeper interior are beneath our feet! What Messenger is looking at is the interior of a planet, which become a planetary surface. Any wonder that NASA is scratching its head?

Science and Technology Facilities Council (2007, July 3). 'Earth And Mars Are Different To The Core, Scientists Find'. ScienceDaily. Retrieved October 21, 2009, from /2007/06/070628162400.htm. Quote: "We were quite startled . . . the heavier isotopes from . . . earth samples contained increased proportions of the heavier isotopes of silicon. This is quite different from meteorites from . . . Mars and the large asteroid Vesta -- which do not display such an effect. . . . unlike Mars and Vesta, the Earth's silicon has been divided into two sorts . . .. at depths the silicates change structure to denser forms so the isotopic make-up would depend on the pressure. . .. This effect is the subject of ongoing studies . . .. the Moon has the same silicon isotopic composition as the Earth." COMMENT: A meteorite splashed to the Earth from the surface of a large body such as Mars or the asteroid Vesta, is scarcely likely to tell us everything that is to be known about the chemistry of those bodies. Samples of the Earth and Moon are likewise taken from the surface or near surface of those bodies and therefore suffer similiar constraints. These constraints notwithstanding, these silicon analyses fit very comfortably with Common Donor-Capture. They suggest that an element currently found in rock at the surfaces of the Earth and Moon may have been subject to temperatures and pressures such as occur in the interior of planets. They strongly suggest that the Earth and Moon have events in their histories different from the histories of Mars and an asteroid. Is this difference bound up in the fact that Mars and the asteroid did not receive large quantities of material from the interior of a donor planet, whilst the Moon and the surface of the Earth did receive materials from the interior of another body?

University of Bristol (2011, September 9). Where does all Earth's gold come from? Precious metals the result of meteorite bombardment, rock analysis finds. ScienceDaily. Retrieved September 20, 2011, from

University of Copenhagen (2011, August 18). Moon younger than previously thought, analysis of lunar rock reveals. ScienceDaily. Retrieved August 21, 2011, from COMMENT: A moon slightly younger than the other planets concurs with formation from another planet.

University of Toronto (2009, October 19). 'Geologists Point To Outer Space As Source Of The Earth's Mineral Riches'. ScienceDaily. Retrieved October 21, 2009, from /releases/2009/10/091018141608.htm.

Wikipedia: 'Angrites', 'Aubrites' and 'EH Chondrites'. These three unusual meteorite types are of interest in regard to moon origin. Additional information is available online. Angrites have features suggestive of an origin near the center of the solar system. EH chondrites and aubrites are exceptional in having oxygen isotopes concomitant with those of the earth and the moon. Aubrites are of particular interest in that they have features suggestive of a possible origin in the planet Mercury. This means that pieces of another planetary body, possibly of Mercury or of some lost planet, are now finding their way to the earth and moon, as we hypothesize happened in the past.

Williams G.E., Science Adelaide News, July 1996 (University of Adelaide, South Australia), Quote: ". . . in late Precambrian times the year contained about 400 days . . . which gives a mean rate of lunar retreat of about 2.05 cm/yr over the last 620 million years. This is little more than half the present rate of lunar retreat . . . the present rate of lunar retreat is . . . high."

Zhang J., et al, The proto-Earth as a significant source of lunar material, Nature Geoscience, 5, 240–241
(2012) Published online 25 March 2012.

References Krauskopf, K. B. 1967. Introduction to Geochemistry. McGraw-Hill/Kogakusha, Tokyo

Taylor, Stuart Ross, 1998 Destiny or Chance: Our Solar System and its Place in the Cosmos Cambridge University Press, Cambridge


This paper was first published 2000 and kept fully updated. As may be deduced from updates in Further Reading this theory of lunar origin may be regarded as proved at least in its general outline.

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