From WASHINGTON UNIVERSITY IN ST. LOUIS
Chemistry says Moon is proto-Earth’s mantle, relocated
Data confirm model in which impact pulverizes Earth like a sledgehammer hitting a watermelon
Tiny differences in the segregation of the isotopes of potassium between the Moon and Earth were hidden below the detection limits of analytical techniques until recently. But in 2015, Washington University in St. Louis geochemist Kun Wang, then the Harvard Origins of Life Initiative Prize postdoctoral fellow, and Stein Jacobsen, professor of geochemistry at Harvard University, developed a technique for analyzing these isotopes that can hit precisions 10 times better than the best previous method .
Wang and Jacobsen now report isotopic differences between lunar and terrestrial rocks that provide the first experimental evidence that can discriminate between the two leading models for the Moon’s origin. In one model, a low-energy impact leaves the proto-Earth and Moon shrouded in a silicate atmosphere; in the other, a much more violent impact vaporizes the impactor and most of the proto-Earth, expanding to form an enormous superfluid disk out of which the Moon eventually crystallizes.
The isotopic study, which supports the high-energy model, is published in the advance online edition of Nature Sep.12, 2016. “Our results provide the first hard evidence that the impact really did (largely) vaporize Earth,” said Wang, assistant professor in Earth and Planetary Sciences in Arts & Sciences.
An isotopic crisis
In the mid-1970s, two groups of astrophysicists independently proposed that the Moon was formed by a grazing collision between a Mars-sized body and the proto-Earth. The giant impact hypothesis, which explains many observations, such as the large size of the Moon relative to the Earth and the rotation rates of the Earth and Moon, eventually became the leading hypothesis for the Moon’s origin.
In 2001, however, a team of scientists reported that the isotopic compositions of a variety of elements in terrestrial and lunar rocks are nearly identical. Analyses of samples brought back from the Apollo missions in the 1970s showed that the Moon has the same abundances of the three stable isotopes of oxygen as the Earth.
This was very strange. Numerical simulations of the impact predicted that most of the material (60-80 percent) that coalesced into the Moon came from the impactor rather than from Earth. But planetary bodies that formed in different parts of the solar system generally have different isotopic compositions, so different that the isotopic signatures serve as “fingerprints” for planets and meteorites from the same body.
The probability that the impactor just happened to have the same isotopic signature as the Earth was vanishingly small.
So the giant impact hypothesis had a major problem. It could match many physical characteristics of the Earth-Moon system but not their geochemistry. The isotopic composition studies had created an “isotopic crisis” for the hypothesis.
At first, scientists thought more precise measurements might resolve the crisis. But more accurate measurements of oxygen isotopes published in 2016 only confirmed that the isotopic compositions are not distinguishable. “These are the most precise measurements we can make, and they’re still identical,” Wang said.
A slap, a slug or a wallop?
“So people decided to change the giant impact hypothesis,” Wang said. “The goal was to find a way to make the Moon mostly from the Earth rather than mostly from the impactor. There are many new models — everyone is trying to come up with one — but two have been very influential.”
In the original giant impact model, the impact melted a part of the Earth and the entire impactor, flinging some of the melt outward, like clay from a potter’s wheel.
A model proposed in 2007 adds a silicate vapor atmosphere around the Earth and the lunar disk (the magma disk that is the residue of the impactor). The idea is that the silicate vapor allows exchange between the Earth, the vapor, and the material in the disk, before the Moon condenses from the melted disk.
“They’re trying to explain the isotopic similarities by addition of this atmosphere,” Wang said, “but they still start from a low-energy impact like the original model.”
But exchanging material through an atmosphere is really slow, Wang said. You’d never have enough time for the material to mix thoroughly before it started to fall back to Earth.
So another model, proposed in 2015, assumes the impact was extremely violent, so violent that the impactor and Earth’s mantle vaporized and mixed together to form a dense melt/vapor mantle atmosphere that expanded to fill a space more than 500 times bigger than today’s Earth. As this atmosphere cooled, the Moon condensed from it.
The thorough mixing of this atmosphere explains the identical isotope composition of the Earth and Moon, Wang said. The mantle atmosphere was a “supercritical fluid,” without distinct liquid and gas phases. Supercritical fluids can flow through solids like a gas and dissolve materials like a liquid.
Why potassium is decisive
The Nature paper reports high-precision potassium isotopic data for a representative sample of lunar and terrestrial rocks. Potassium has three stable isotopes, but only two of them, potassium-41 and potassium-39, are abundant enough to be measured with sufficient precision for this study.
Wang and Jacobsen examined seven lunar rock samples from different lunar missions and compared their potassium isotope ratios to those of eight terrestrial rocks representative of Earth’s mantle. They found that the lunar rocks were enriched by about 0.4 parts per thousand in the heavier isotope of potassium, potassium-41.
The only high-temperature process that could separate the potassium isotopes in this way, said Wang, is incomplete condensation of the potassium from the vapor phase during the Moon’s formation. Compared to the lighter isotope, the heavier isotope would preferentially fall out of the vapor and condense.
Calculations show, however, that if this process happened in an absolute vacuum, it would lead to an enrichment of heavy potassium isotopes in lunar samples of about 100 parts per thousand, much higher than the value Wang and Jacobsen found. But higher pressure would suppress fractionation, Wang said. For this reason, he and his colleague predict the Moon condensed in a pressure of more than 10 bar, or roughly 10 times the sea level atmospheric pressure on Earth.
Their finding that the lunar rocks are enriched in the heavier potassium isotope does not favor the silicate atmosphere model, which predicts lunar rocks will contain less of the heavier isotope than terrestrial rocks, the opposite of what the scientists found.
Instead it supports the mantle atmosphere model that predicts lunar rocks will contain more of the heavier isotope than terrestrial rocks.
Silent for billions of years, the potassium isotopes are finally found a voice, and they have quite a tale to tell.
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Full study here: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature19341.html
This is pretty cool stuff. It’s likely we’ll never know for sure, we can’t time travel, yet. But, until we do a heck of a lot more exploration of the moon and gather a lot more data it’ll remain a plausible theory, and nothing more. Still, pretty cool stuff.
I’d be afraid to send anything back to look. From current theories, it looks like it was far from a sure thing that our solar system would end up as friendly to life as ours is. Even a small perturbation, over 4+ billion years could result in a big change today.
But higher pressure would suppress fractionation, Wang said. For this reason, he and his colleague predict the Moon condensed in a pressure of more than 10 bar, or roughly 10 times the sea level atmospheric pressure on Earth.
I have problems with this theory based upon the above quote. Here are my questions:
The hypothesis is that we have “supercritical-fluid” silicates at 10+ bar and sufficiently high temperature to be above the critical point …. at an earth radii in the vicinity of the moon.
1. How much energy is required to vaporize all that mantle and impactor? (note, the earth’s mantle was already hot and under thousands of atmospheres of pressure at initial conditions — it probably matters.)
2. Does that much energy exist in the collision of two planetary masses coming together at, say 15-18 km per sec? We aren’t talking about the energy to fling a mass as large as the moon to near earth escape velocity. No. We need that much energy PLUS the energy to vaporize that mass to the point of supercritical-fluid and 10bar at the radii of the moon.
2a — what lunar formation radii is compatible with this theory. It would be much closer to the earth than the moon is today. But how close CAN it be for the condensation to work?
3. Suppose you got an ‘atmosphere’ of silicates at that temperature and pressure. Wouldn’t a large bulk of the mass reach escape velocity from thermodynamics alone?
4. If things were that hot and gaseous, how is it the earth has any light elements at all? These elements would preferentially escape gravity. (see Q3 above).
Addendum: Why 15-18 km per sec?
Earth escape velocity is about 11.5 km per sec. So any body striking earth would have that speed as a minimum. A smaller body (the impactor) would have it’s own escape speed and would add to that 11.5.
The earth’s velocity around the sun is 30 km per sec. So it is theoretically possible to have a head on collision (60 km/sec) , but that would require the impactor to be in retrograde motion. A more realistic assumption is that the impactor is moving roughly in the same direction around the sun as Earth, but the orbits chaotically intersected at some point. In this case, the differences in orbital speeds are small and the impact speed is govern by mutual gravitation.
Another possibility, I suppose, is that the impactor was in a cometary orbit. In which case the collision speed would be in the 40-55 km/sec range. But then wouldn’t post collision gravitational capture be most unlikely?
The earth as we know has an almost circular orbit. A major collision with an object in a cometary orbit would have significantly perturbed the earth’s orbit, making it much less circular.
Good answer, MarkW. But wouldn’t 4 billion years of orbital resonances circularize the orbit?
It does beg the question of why Mercury’s orbit is so elliptical. Was it hit by something comparatively big and fast?
Answer to 2a: There is a table -in Wikipedia [Roche limit (fluid)] which states the Roche limit for a comet sized body with a “fluidized” rather than solid composition is greater than 34,000 km. Since the theory is that the Moon condensed out of an atmosphere, it started out small and grew. Therefore by this theory, the moon had to condense at a radius of at least 34,000 km. Geosynchronous orbits are at 42,164 km.
From this Delta-V chart of the solar system:
it seems that the energy to reach geosynchronous is about 90% of the energy to reach escape velocity. So the fluid Roche-limit must be 80-85% of escape velocity.
To me that is too little margin for error for the “high-impact” supercritical fluid theory. You must get matter beyond the fluid Roche radius, but give it 20% more and the matter escapes into space. That theory won’t hunt.
The Roche radius is smaller ( under 19,000 km) if you start with solid cores around which ejecta can accumulate. But that is the Scenario 1 and the magma disk.
We aren’t launching a single body to a single orbit.
I would presume that a non-trivial amount of matter was given enough energy to reach escape velocity.
There was a lot of matter that was given little enough energy that it fell back to earth over the next few centuries.
Other matter that was given energy to reach orbits both higher and lower than the moons were eventually pulled into the forming moon. Other objects had their orbits perturbed enough so that they were either ejected from the earth/moon system, or fell back to the earth.
@MarkW. Yes, I agree with all that, but the argument applies to both the subject scenarios, and on balance applies to Scenario 1 more than Scenario 2. I prefer Scenario 1 since I don’t have to vaporize all the rock. — I just have to “launch” and scatter it into obit.
Re point 2. The Moon has been moving outward due to tidal orbital decay, so it is much further out now than it was billions of years ago. By the same mechanism, Earth is rotating considerably slower. A much faster rotating Earth means the the geosynchronous orbital distance would have been much closer in. We know that the Moon formed outside the then geosynchronous orbital distance, because that is a requirement of tidal orbital decay moving it outward, if it had been inside the distance, the Moon would have been pulled inward.
@LarryD — The moon had to form above the geosynchronous orbit (at the faster early Earth rate) or tidal friction would have worked in reverse, causing the moon to slow down and fall closer to the earth and eventually cross the Roche limit and break up.
My main point about Geosynchronous orbits was to compare the Roche (cometary fluid) radius of 38,000 km to a known orbit (42,164 km) with known energy levels compared to escape velocity. Geosynchronous orbit was used for an energy benchmark.
Why are planets “round” and not just heaps of what they have managed to accrete ?
Gravity
OK, but lets add time.
Minor typo in the title: should be “its mantle,” not “it’s mantle”.
Measurements of an element in Earth and Moon rocks…
First you have to assume those moon rocks actually came from the moon…
http://oldsite.david-tyler.com/uploaded_images/moon%203-4-09%2016%20x%209%20%20Stoffler%20Maginus.jpg
… and then you have to assume for this purpose that a sample of seven rocks a few hundred rocks scooped up from the surface at only six clusters, that is manned landing locations that were practically accessible (1), is an adequate representation of what the moon is made of.
(1) Crater Tycho for instance was considered for a landing site, but the orbit and lunar lander flight path was judged risky and used too much fuel and weight. Tycho was kept on the list for the last “J” mission, probably Apollo 20.
I don’t think there is any doubt the rocks came from the Moon.
There is little doubt that the rocks brought back from the moon came from the moon. I think the point of the photo and associated question is “where were the rocks BEFORE they came to lay on the surface of the moon.?”
The moon rocks came from the sound stage somewhere in Arizona…
/sarc…
Yeah J,
I think that’s what I read that Lew believes…We never went to the moon.
He published his survey results (and also withheld some survey data) to try to prove his belief.
Has anyone ever wondered why the moon’s craters are so uniform in depth? That always seemed strange to me.
I have wondered about that as well but if all these impacts happen all in the same time frame ( a short geological time frame) so they would have hit when the surface of the moon would have reacted the same for each impact. I would compare it to something hitting a soft surface but a few “days” later that same surface would be “frozen” and so react differently, does that make sense?
There are some other ideas about at least some of those craters:
Nonsense on stilts. I gave up when they declared that a single rock could conclusively prove that the entire moon had been bombarded at various times in it’s history.
A single rock would record local impacts, and that’s all.
PS: A grand total of nobody has ever claimed that Jupiter and Saturn combined to eject another large body from the solar system.
A lot of the big craters were formed when the moon was still young. Magma flowing in leveled out the craters.
Has anyone explained the hexagon shaped craters on some of Saturn moons?
Sorry gotta go…hit run or drive by as someone refers to my posts like this. But impactors can be fun…
“”The moon is not round—it is shaped like an egg. e
http://www.randomhistory.com/photos/2010/moon-egg.jpg
The volume of Earth’s moon is the same as the volume of the Pacific Ocean. e
e Graham, Ian. 1999. The Best Book of the Moon. New York, NY: Kingfisher Chambers Inc.””
http://facts.randomhistory.com/moon-facts.html
The volume of Earth’s moon is the same as the volume of the Pacific Ocean
No.
The area of the moon is less than that of the Pacific Ocean. About 1/4 the area.
But the volume of the moon is about 30 time bigger than the volume of the Pacific. The Pacific is on average only 4 km deep.
In fact, all the worlds oceans make up only about 1/16 of the moon’s volume.
We don’t even know where nor if there were continents prior to an impact of this magnitude. Comparing modern earth features to some imaginary impact and imaginary earth long ago doesn’t seem like science. I have to admit being previously impressed by the Pacific Ocean/Moon conjecture forty years ago or so, but it makes little sense now.
Even if they earth had continents at that early date, it wouldn’t have mattered since the impact would have completely melted the earth’s surface.
If this actually happened, wouldn’t some earth rocks extracted & studied be EXACTLY the same as the moon rocks studied?
The most pertinent comment above is whether 7 lunar rocks is sufficient sample size to conclude they represent the make up of the entire moon. Not very convincing in my book. Same for the Earth samples.
The observation that “planetary bodies that formed in different parts of the solar system generally have different isotopic compositions” is quite reasonable, given that the entire solar system condensed from the plasma cloud formed in a nova. The similarity of the isotopic compositions of the proto-earth and Theia could be accounted for if they both formed at about the distance from the sun – co-orbitally. A co-orbital origin would also account for the relatively low kinetic energy of the impact required to leave the present earth-moon system rather than a belt of shattered planetoids.
Roche Limit: “The shortest distance at which a satellite not held together by any force other than its own gravity can orbit another celestial body without being torn apart by the tidal force between them. The distance depends on the densities of the two bodies and the orbit of the satellite. If the satellite and the object are of similar densities, the Roche limit is about two and a half times the radius of the larger object. Since most natural satellites are rigid bodies, their tensile strength allows them to orbit much closer than their Roche limit; however, rigid bodies too may be broken up by tidal forces.”
Small particles can form inside the Roche Limit, as atoms form molecules and molecules bind to one another, the Roche Limit just imposes a size limit on the particles. If tidal friction moves the cloud of particles outward, then they can aggregate to form a moon, after they move outside the Roche Limit.
Using the rule of thumb and Earth’s current radius (6,371 km), the Roche Limit is somewhat over 15,000 km (from Earth’s center, or over 9,000 km from the surface).
The hardest part of the new theory to swallow is the 10 bar extended silicate atmosphere.
I would imagine that the size of the object would impact the Roche limit. After all, the larger the object, the greater the gravitational difference between the inner most and outer most points of the object.
As an example, we have quite a few satellites that orbit only about 100 miles or so up, yet they aren’t being torn apart.
The Roche limit of a two body problem is dependent upon the primary mass and the mass and composition of the secondary. The greater the mass of the secondary the smaller will be the Roche limit of the pair because the secondary has its own greater mass to hold itself together.
The Scenario 2 discussed in the main paper, is the absolute worst case (largest value) for the Roche limit. The secondary must start out as a greater-than-average density cloud in the “silicate atmosphere”. Therefore the fluid Roche limit should be used, greater than 38,000 km for the (current) mass of the Earth. The seed of the Moon in this scenario is a cloud with no tensile strength and weak gravity.
Earth satellites hold together because they have high tensile strength. But should a satellite split in two, like a tethered satellite, the two parts will separate. The miniscule mutual gravitation of the two parts are no match for the tidal forces of Low Earth Orbit.
@LarryD, Yes, the 10 bar silicate atmosphere at the radius consistent with a fluid Roche limit is very hard to swallow. But let’s suppose we do swallow it: 10 bar silicate atmo (at greater than 3000+ degrees C). What should be the pressure curve as a function of Earth radius? I think you would be forced to have many thousands of bar (at an incredible temperature!) will above the current surface of the earth. There isn’t that much mass available in our current Earth – Moon system. Scenario 2 has far too many problems compared to Scenario 1.
We have 4B yrs (proto-earth) of the same meteoritic material raining down on both bodies and likely bombardment of
a large amount bolides in the early years. The surface samples taken by astronauts represent this material. Why would we be surprised they had similar geochemistry? S’Truth! As a mining exploration geologist, I’d be fired for a sampling job like this?
Bodies have different isotopic ratios if they form at different distances from the sun. If the body that collided with the earth formed in a similar orbit as did the earth, than it’s isotopic rations would be very nearly identical.
My favorite hypothesis about how the Moon formed was as the result of a massive fission explosion that blew out one side of the planet, leaving a hole that eventually filled in with ocean, the resulting crustal fractures on the opposite side of the planet kicked off plate tectonics,brought some heavier elements closer to the surface and it left the Moon in its wake. In effect, the Earth is the remnants of a very short lived fission star.
4.5 B years ago, the U235/U238 ratio was at least 3-4% which as it was separated by gravity in the core to become a shell of U235 surrounding a core of U238 and lead and this shell went critical.
An interesting feature of this hypothesis is that its far more likely to occur than the extremely precise collision otherwise required, which means that there are likely to be many other planets in the Universe that have a similar moon.
An explosion of sufficient magnitude to launch an object the size of the moon into an orbit out past the Roche limit, would have completely shattered the rest of the planet, leaving just an expanding cloud of debris in it’s wake.
Markw,
“leaving just an expanding cloud of debris”
This is more or less what the article says happened, except that the cloud was gaseous although gravity will surely pull it back together. If the explosion was uniform, you can envision the surface expanding outwards and collapsing back in without forming a Moon, which is a possibility for what happened on Venus when its U235/U238 ratio was high enough for gravity to induce fission. An asymmetric explosion would blow out only one side of the planet and that could be what happened on Earth.
First off, I said expanding. The violence of the explosion would have been sufficient to give the remaining particles enough energy to escape the mutual gravitation.
PS: You don’t need to fracture the crust in order to get plate tectonics started.
Secondly, how do you get those radioactive elements close enough together to create the explosion.
In the real world, as those elements got closer together over thousands to 10’s of thousands of years, the rate of decay would gradually increase, as the rate of neutron bombardment very gradually increased.
As a result, even as concentration increased due to some mythical forces, the concentration was decreasing due to the interaction of the uranium atoms.
The end result is an increase in heat, but no boom. Despite what Ivanova says, there is not always a boom.
“Secondly, how do you get those radioactive elements close enough together to create the explosion.”
Gravitational separation, similar to the way that a centrifuge works.
“due to some mythical forces,”
Gravity is not a mystery.
“the rate of decay would gradually increase, as the rate of neutron bombardment very gradually increased.”
Once neutron bombardment gets high enough, it’s the definition of going critical.
First off, gravity would take millions of years to concentrate the uranium sufficiently. And that’s without convection constantly keeping things stirred up.
Due to the time it takes to concentrate, neutron bombardment will never get high enough to create an explosion. As I explained earlier, when the concentration proceeds slowly, the gradual increase in neutron bombardment burns off the uranium long, long before it can reach critical mass.
If an atomic bomb took 100 years to bring the masses together, and the two masses in this case is pretty close to 100% pure, the bomb would never explode. It would be pure lead long before the two masses got close enough.
“neutron bombardment will never get high enough to create an explosion”
You need to reassess this in light of a much higher primordial U235/U238 ratio, which would even be far larger than a few percent if the primordial U235 was also being consumed at a significantly faster rate then it would ordinarily decay at its half life of about 700M years. It’s also quite possible that an ordinary impact event could have been the trigger as a shock wave from a surface impact passes through the core.
Doesn’t matter. It can’t get together fast enough to reach critical mass. EVER.
Unless you can figure out a way to concentrate all of the unstable U isotopes in a small area, IE no more than 100 feet across, and do it in a matter of minutes, you will not be able to reach critical mass.
That reminds me. Merely have more uranium is meaningless if you can’t seperate the fissionable isotopes from the non-fissionable ones. Gravity isn’t going to do it. The difference in mass is way, way, way to small.
The best you could ever hope for is a bit more heat than might otherwise have been generated.
I agree with you, Mark.
The force of gravity gets smaller and smaller as you approach to core. It is for this reason I am not a fan of convection as the primary driver of plate tectonics. I am a [“Slab Pull” with “Ridge Push” assistance] adherent. I think it best explains the formation of back-arc island chains, horst-graben landscapes, and continental rifting and volcanic chains.
I do like the low-level core fission model. Fission must be going on in the core, if even at very low activity levels. The question is how much of the core’s heat generation is by
A) radio-active decay of the primordial soup material,
B) how much is direct fission energy release, and
C) how much is radio-active decay of fission daughter products?
None of these quantities are zero, but are B and C significant compared to A?
What really attracts me to the core fission model is it provides a way for the earth to have a NON_CONSTANT, oscillating radius over geologic time scales. I’m no “Expanding Earther”, but a radius that oscillates one part in 3000 over a period of 10,000 years helps the mechanism of plate tectonics immensely.
Early on in the Manhattan Project, the reactor physicists got a nasty surprise when their first plutonium breeder reactor at Hanford went into unexpected oscillation. Fission daughter products were poisoning the reactor. Some of these poisons had half-lives in the units of hours or days. So once the reactor created the daughters, it dropped in intensity until the poisons dropped below a threshold, then the reactor would spin up again. They solved the problem by putting more U-235 in the reactor than originally designed by the physicists. The reactor design engineers had allowed for more uranium because they new the physicists were guessing at a lot of the specs since it had never been done before.
Those reactor poisons would also exist in any core fission reaction. Given the immense size of the core that could participate in fission (hundreds of miles in diameter), the concentration of poison products could vary over a long time. So, it become possible for the fission in the core to be non-constant. It follows, then that the temperature of the core would oscillate with the rate of fission. If the temperature of the core oscillates, then the radius of the earth would oscillate, too, from thermal expansion.
The radius of the earth wouldn’t have to change much…. maybe one part in 5000 over the span of 10,000 years. But what would that buy you? It give a circumference of the earth that is not constant, expanding and contracting over a geologic time scale. This give us a ratchet mechanism to initiate and perpetuate plate tectonics via rifting (during expansion) and subduction (during contraction) in addition to the other proposed tectonic forces.
The test of this theory can come from geoneutrino experiments and discovery that their detection level changes over decades.
I think WUWT commenters have collectively given a better context to the serious doubt one should read such reports with. Question is – how much should the tax payer be contributing to these science fiction/fantasy essaying scientits? – oops typo, but, wait a minute, perhaps not… 🙂
I think Pluto and Charon are an excellent example to take notice of in moon creation theory. They act as two bodies circling a central point between them. It could be a death spiral that would lead them to smash into each other or they could be an example of how similar, yet different bodies can attract one another from within the same orbital path.
What bothers me about the cosmic marble game theory is the exacting conditions that needed to occur to produce the required results. The universe is chaotic, not exacting. We took our moon rocks from impact sites. We have yet to see much of anything below the surface of the bombardment debris. Even the recent detonation to search for water possibilities only managed to stir up surface dust. I’m glad their model is working for them but its reality may not necessarily be what actually occurred. We learn more by sending out probes then we ever do by modeling anything. I have an old science book where they set out Saturn’s ring composition and how they formed… one fly by and all of that was proved to be the flight of imagination that it was. I suspect this will be much the same.
Saturn’s rings are maintained by something, EM maybe, that is patently obvious. To uniform and undisturbed to be “gravity” alone
If you see the universe through explosions and gravity it really does limit the theory.
Earth may have just captured the moon from another body in the past. While you’re theory can disprove another theory, no one can prove their own theory on the moon.
First off, the fact that the material that the moon and the earth are made of is nearly identical is solid evidence that the moon did not form in another part of the solar system.
Secondly, it’s impossible for the earth to have captured the moon without the help of a third body to siphon off enough of the moon’s momentum so that it could be captured.