Or that the mix of Earth and Theia in the moon is very non homogenous and they took most of their samples from the Earths part.
Actually, now that I think about it, wouldn't the result of the collision cause most of Earths contribution to be on the surface of the moon? If it was otherwise, then Earth would have had an ring much like Saturn at one point which then collected into whole to become the moon. That couldn't be true since we would have easily seen evidence on the moon. This theory of mine would mean that almost any samples taken from the moon would would be originally from Earth.
The giant impact theory predicts that Earth did, at one point, have a proto-ring of debris from the collision. That proto-ring slowly accreted into the moon.
I'm not sure what evidence we would expect to observe on the moon to indicate whether it accreted from a proto-ring or was captured intact - could you elaborate a little?
I'm being picky here, but the word "proven" doesn't really make sense in the context. A more accurate way of expressing the title would be "Evidence supports a different theory" or "Less support for this theory", as theories can never be proven.
If theories could be "proven" in the mathematical sense then they wouldn't be falsifiable and therefore it wouldn't be a "theory" in any scientific meaning of the word. So yes, I completely agree with your being picky about this!
> If theories could be "proven" in the mathematical sense then they wouldn't be falsifiable
Ack! This is not what "falsifiable" means.
Falsifiability is the property that states, there exists some hypothetical evidence which would be accepted as conclusive disproof of the theory. For instance, newton's third law ("equal and opposite") can be falsified by the discovery of a method of applying force which avoids any opposite application.
Extrapolating some, we can see that for all falsifiable theories, there is an extensive class of evidence which doesn't quite prove the theory wrong, but does weigh against the theory. Non-falsifiable theories don't have this property - for any method of assigning a probability of correctness to a non-falsifiable theory, there is a positive number below which that probability cannot go.
The reason the giant-collision theory should not be said to be "proven" incorrect is that it has not been. Its probability of correctness is still non-zero (and significant). However, it's not true that scientific theories cannot be "proven" incorrect - classical mechanics has been, for instance.
In what sense can a scientific theory be "proven" correct of incorrect in the same way that a purely mathematical statement can? Aren't they two completely different things - with the mathematical argument being binary (it's either true or false) and the scientific argument, as you say, involving degrees of confidence based upon supporting or contradictory evidence?
[Of course, a scientific theory could be disproven by being based on incorrect mathematical reasoning - but that's presumably not very interesting]
I don't understand. If "theia" hit earth and formed moon, why would the istopic signatures be any different. Now both earth and moon come from same pair of different objects.
We would expect different proportions of the isotopes on the Earth and the Moon. This is because the Moon according to the models would have a greater proportion of its mass made up of the theorised collider "Theia" than Earth.
In this particular experiment they showed the isotopic proportions matched between here and the Moon.
My understanding of the theory is that Theia hit the earth, that most of it was absorbed into the earth's surface/ molten core, and that the rest, along with some of the earth was ejected out into space.
If that's the case I don't see how there is any way of 'proving' that the isotopic signatures we are matching with those of the moon are 'native' and not already part of some Earth/Theia mix - in which case they'd match with a Moon that was already part of an Earth/Theia mix. Without knowing the composition of the earth 4.5 billion years ago, I'm not sure you can say otherwise?
If the giant impact theory is correct, Theia must have been about the same size as Mars - roughly a tenth of the mass of the earth. Hence it would have a much larger impact on the makeup of the moon than it would on the makeup of the earth - a difference we would expect to be able to detect if the theory is correct.
It would have a negligible impact on the makeup of the Earth as a whole, but should have a large impact on the composition of Earth's crust (and the mantle, to a lesser extent.) It seems to me that the Theia theory should also predict that Earth's crust and Moon's crust (which are the only parts we can get samples of!) have quite similar composition.
I think we should remember the vast differences between reporting about scientific papers and the peer-reviewed papers themselves; I have a good feeling, based on previous experience, that most of the caveats raised here will be tackled by the paper, whose tone will probably be less decisive.
Indeed, according to the abstract (http://www.nature.com/ngeo/journal/v5/n4/full/ngeo1429.html) the paper only presents (additional) evidence against the hypothesis that 40% of the moon material comes from Theia. But it doesn't reject the hypothesis that the moon was formed by an impact:
The isotopic homogeneity of this highly refractory element suggests that lunar material was derived from the proto-Earth mantle, an origin that could be explained by efficient impact ejection, by an exchange of material between the Earth’s magma ocean and the protolunar disk, or by fission from a rapidly rotating post-impact Earth.
One thing I've never understood about this model: according to orbital mechanics, you can't "boost" yourself into an orbit that doesn't include the point you're already in. So if the mass that became the moon started at the surface of the earth, its orbit would just smash it back into the earth again. You can see what I mean here: http://isthis4real.com/orbit.xml
In a 2-body system this is true, but adding many more bodies to the system makes things very chaotic. An object passing by or colliding with the "proto-moon" could easily deflect it from its crash course. Whether that's probable given the evidence is a different question, but mathematically it absolutely is possible.
And that's even assuming that the "mass" is more or less solid - if it were ejected from a violent impact it's more likely that it would be more of a cloud of debris, in which case things get even more complex. So many "bodies" are involved that it becomes more of a fluid dynamics problem than an orbital mechanics one. The individual particles in the cloud interact with each other gravitationally, deflecting each other from their "return-to-sender" orbit. Parts of the cloud would fall to earth, parts would escape to space, and parts would stay in orbit to become a ring system or (as is hypothesized) one or more moons.
The theorized situation isn't so much like skipping a stone across the earth as totally vaporizing a big chunk of both the earth and the planet that hit it, and a fairly small part of the resulting cloud (about half according to some models) of debris managing to end up in orbit and eventually collapsing into a single body (the moon).
The theory was merely proven to be theoretically falsifiable, and not incorrect. They clearly state in the article that they couldn't find any proof of two parents, which for the moment points to the moon having only one parent. This contradicts the previous theory, but doesn't make it false.
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[ 3.1 ms ] story [ 52.9 ms ] threadActually, now that I think about it, wouldn't the result of the collision cause most of Earths contribution to be on the surface of the moon? If it was otherwise, then Earth would have had an ring much like Saturn at one point which then collected into whole to become the moon. That couldn't be true since we would have easily seen evidence on the moon. This theory of mine would mean that almost any samples taken from the moon would would be originally from Earth.
I'm not sure what evidence we would expect to observe on the moon to indicate whether it accreted from a proto-ring or was captured intact - could you elaborate a little?
Ack! This is not what "falsifiable" means.
Falsifiability is the property that states, there exists some hypothetical evidence which would be accepted as conclusive disproof of the theory. For instance, newton's third law ("equal and opposite") can be falsified by the discovery of a method of applying force which avoids any opposite application.
Extrapolating some, we can see that for all falsifiable theories, there is an extensive class of evidence which doesn't quite prove the theory wrong, but does weigh against the theory. Non-falsifiable theories don't have this property - for any method of assigning a probability of correctness to a non-falsifiable theory, there is a positive number below which that probability cannot go.
The reason the giant-collision theory should not be said to be "proven" incorrect is that it has not been. Its probability of correctness is still non-zero (and significant). However, it's not true that scientific theories cannot be "proven" incorrect - classical mechanics has been, for instance.
[Of course, a scientific theory could be disproven by being based on incorrect mathematical reasoning - but that's presumably not very interesting]
In this particular experiment they showed the isotopic proportions matched between here and the Moon.
If that's the case I don't see how there is any way of 'proving' that the isotopic signatures we are matching with those of the moon are 'native' and not already part of some Earth/Theia mix - in which case they'd match with a Moon that was already part of an Earth/Theia mix. Without knowing the composition of the earth 4.5 billion years ago, I'm not sure you can say otherwise?
The isotopic homogeneity of this highly refractory element suggests that lunar material was derived from the proto-Earth mantle, an origin that could be explained by efficient impact ejection, by an exchange of material between the Earth’s magma ocean and the protolunar disk, or by fission from a rapidly rotating post-impact Earth.
And that's even assuming that the "mass" is more or less solid - if it were ejected from a violent impact it's more likely that it would be more of a cloud of debris, in which case things get even more complex. So many "bodies" are involved that it becomes more of a fluid dynamics problem than an orbital mechanics one. The individual particles in the cloud interact with each other gravitationally, deflecting each other from their "return-to-sender" orbit. Parts of the cloud would fall to earth, parts would escape to space, and parts would stay in orbit to become a ring system or (as is hypothesized) one or more moons.
The theorized situation isn't so much like skipping a stone across the earth as totally vaporizing a big chunk of both the earth and the planet that hit it, and a fairly small part of the resulting cloud (about half according to some models) of debris managing to end up in orbit and eventually collapsing into a single body (the moon).