How was the age of the Moon determined?

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dougettinger
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How was the age of the Moon determined?

Post by dougettinger » Wed Jun 02, 2010 11:03 pm

The Moon is covered with impact basins and lava flows created from impacts. Some highlands possibly not disturbed by impacts or eruptions are radiometrically dated as forming 4.4 billion year ago. So how do scientists propose its formation at 4.527 + or - 0.010 bya ?

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Re: How was the age of the Moon determined?

Post by alter-ego » Sun Jun 06, 2010 2:00 am

dougettinger wrote:The Moon is covered with impact basins and lava flows created from impacts. Some highlands possibly not disturbed by impacts or eruptions are radiometrically dated as forming 4.4 billion year ago. So how do scientists propose its formation at 4.527 + or - 0.010 bya ?
This is only one source, but it answers your question pretty well, I think.

<<More recent research measured tungsten content in rocks returned from the moon. Tungsten-182 is what you get when hafnium-182 decays. So the scientists measured the ratios of tungsten to hafnium to determine exactly when the moon formed. This is where the number 4.527 billion years (give or take 10 million years).>>

http://www.universetoday.com/guide-to-s ... -the-moon/

Post Script I responded more to the question posed in the topic title, but the article does mention near identical measured oxygen isotop ratio(s) between the Earth and moon, and provides other links that may better answer the question you asked in the message. :idea:
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Re: How was the age of the Moon determined?

Post by dougettinger » Wed Jun 09, 2010 2:52 pm

alter-ego wrote:
dougettinger wrote:The Moon is covered with impact basins and lava flows created from impacts. Some highlands possibly not disturbed by impacts or eruptions are radiometrically dated as forming 4.4 billion year ago. So how do scientists propose its formation at 4.527 + or - 0.010 bya ?
This is only one source, but it answers your question pretty well, I think.

<<More recent research measured tungsten content in rocks returned from the moon. Tungsten-182 is what you get when hafnium-182 decays. So the scientists measured the ratios of tungsten to hafnium to determine exactly when the moon formed. This is where the number 4.527 billion years (give or take 10 million years).>>
Hafnium 182 decay has a starting point. How do scientists know when it started to decay ? Do they assume it started near the formation of the solar system and why if that is the case ?

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Re: How was the age of the Moon determined?

Post by bystander » Wed Jun 09, 2010 3:56 pm

dougettinger wrote:Hafnium 182 decay has a starting point. How do scientists know when it started to decay ?

Ratio of Tungsten-182 to Hafnium-182. Same principle used in any radio-isotope dating.

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Re: How was the age of the Moon determined?

Post by dougettinger » Wed Jun 09, 2010 7:12 pm

The starting point is when closure temperature occurred - presumably when the moon originally accreted and was entirely molten. Unlikely, the dating could be incorrect, if the Moon is older and final accretion obliterated or melted all older rock. Also, later bombardments could have created meteorites and/or regolith that is younger than the first rock that soldified. I looked up radiometric dating and answered for myself. The starting date is when the daughter nuclide is heated that have been accumulated over time and is lost through diffusion, setting the isotopic clock to zero. Thanks for you help.

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Re: How was the age of the Moon determined?

Post by Beyond » Wed Jun 09, 2010 8:35 pm

Being the "dumb" bunny about lots of things that i am, i should think that if you really wanted to make sure you have the correct age of the Moon, you would have to get samples from beneath the surface that were not contaminated from all the "stuff" that has hit the outside of the moon.
It could turn out that ALL the rocks on the Moon have come from Meteors and the like that may have been made about the same time, but not the same time as the Moon came into being. At times we have to stop and remember that there are lots of strange things going on all over and sometimes, things just are not what they seem to be.
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Re: How was the age of the Moon determined?

Post by Chris Peterson » Wed Jun 09, 2010 9:59 pm

beyond wrote:It could turn out that ALL the rocks on the Moon have come from Meteors and the like that may have been made about the same time, but not the same time as the Moon came into being.
The analysis of sampled moon rocks and lunar meteorites involves looking at oxygen isotope ratios. When lunar samples are compared with surface rock samples from the Earth, all are found to lie on a single line called the Terrestrial Fractionation Line. This by itself isn't sufficient for dating, but does very reliably argue that the materials came from exactly the same source at the same time. Meteorites are not found to lie on this line. Other isotope ratios are then used for actual dating.
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Re: How was the age of the Moon determined?

Post by dougettinger » Fri Jun 11, 2010 12:57 am

Chris Peterson wrote:
beyond wrote:It could turn out that ALL the rocks on the Moon have come from Meteors and the like that may have been made about the same time, but not the same time as the Moon came into being.
The analysis of sampled moon rocks and lunar meteorites involves looking at oxygen isotope ratios. When lunar samples are compared with surface rock samples from the Earth, all are found to lie on a single line called the Terrestrial Fractionation Line. This by itself isn't sufficient for dating, but does very reliably argue that the materials came from exactly the same source at the same time. Meteorites are not found to lie on this line. Other isotope ratios are then used for actual dating.
Does this Terrestrial Fractionation Line include rocks on Mars ? You speak of lunar samples compared with surface rock samples from the Earth. Are these lunar samples Moon rocks or lunar meteorites ? Your explanation is not clear.

It is quite possible that the Later Heavy Bombardment involved both Earth and the Moon, and consequently, produced similar oxygen isotope ratios. Please check my thought process. Thanks.

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Re: How was the age of the Moon determined?

Post by Chris Peterson » Fri Jun 11, 2010 1:22 am

dougettinger wrote:Does this Terrestrial Fractionation Line include rocks on Mars ?
The small number of Martian rock samples (all meteorites) do not have oxygen isotope ratios that lie on the TFL. It is assumed, therefore, that Mars did not form at the same solar radius as the Earth.
You speak of lunar samples compared with surface rock samples from the Earth. Are these lunar samples Moon rocks or lunar meteorites ?
Both.
It is quite possible that the Later Heavy Bombardment involved both Earth and the Moon, and consequently, produced similar oxygen isotope ratios.
It also also included Mars. But the oxygen isotope ratios of Martian material appear to be different. The LHB presumably contributed negligible new mass to any planets (or the Moon) in comparison with their existing mass, and involved bodies of sizes that only resulted in surface modification, not modification of entire bodies. I don't think there is any support for the LHB making any sort of radical change in the isotope ratios of planets.
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Re: How was the age of the Moon determined?

Post by dougettinger » Fri Jun 11, 2010 1:48 am

Is the oxygen isotope ratio considered uniquely different for each orbital distance from the Sun as you hinted ? Is this ratio linear between the Earth-Moon, Mars, and the Asteroidal orbital regions ? I am sorry. I am probably appearing like a crazed student with all these questions.

Is there any chance that the Later Heavy Bombardment was caused by ejecta from the Earth-Moon collision scenario 3.9 bya ?

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Re: How was the age of the Moon determined?

Post by Chris Peterson » Fri Jun 11, 2010 1:58 am

dougettinger wrote:Is the oxygen isotope ratio considered uniquely different for each orbital distance from the Sun as you hinted?
It is different for materials that appear to have been created under different conditions. The most common assumption is that it is related to differences in the presolar and parasolar nebula, which probably means differences in radial position. But there are a lot of unknowns. I'd say nobody is very confident what it all really means.
Is this ratio linear between the Earth-Moon, Mars, and the Asteroidal orbital regions?
I don't think so. One problem is that there isn't enough material to test to get good statistics. Very little material is associated with bodies which have a known position of formation (none, in fact, but some can at least have reasonable guesses applied).
Is there any chance that the Later Heavy Bombardment was caused by ejecta from the Earth-Moon collision scenario 3.9 bya?
I've not heard it suggested. Something like the Nice scenario or some other perturbation induced scenario seems to be much more likely. Most debris from the collision that created the Moon would probably be ejected from the Solar System completely, or end up in the inner System where it would have been cleared long before the LHB.
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