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This led me to thinking, how do we determine the age of the sun? I would have thought some radio spectrometry, but according to NASA[0]: >We look at the age of

by 37 5y ago

This led me to thinking, how do we determine the age of the sun? I would have thought some radio spectrometry, but according to NASA[0]: >We look at the age of the whole solar system, because it all came together around the same time. >To get this number, we look for the oldest things we can find. Moon rocks work well for this. When astronauts brought them back for scientists to study them, they were able to find out how old they are. [0] https://spaceplace.nasa.gov/sun-age/en/ https://spaceplace.nasa.gov/sun-age/en/

politician 5y ago
Isn't it kind of weird to use the Moon to benchmark the age of the solar system when it's well known that the Moon formed after another body collided with the Earth? The Moon is younger than the Earth.
- tshaddox 5y ago
  I assume it’s because the Moon is geologically inactive and thus the rocks we got from the surface are expected to be essentially as old as the Moon itself.
- pdonis 5y ago
  Not to benchmark, precisely, but to give a lower limit on the age that will likely be longer than any other lower limit we could obtain at our current or near future level of technology.
- vlovich123 5y ago
  If Theia is older than the Earth, then wouldn't the Moon also be older?
  - politician 5y ago
    AIUI, the heat of the collision would've melted everything that wasn't already molten. Any "age" information would be lost as the system cooled. At least, that's my understanding from playing with Universe Sandbox.
    - vlovich123 5y ago
      That would only be the case for the piece that collided though right? The side that wasn’t part of the collision should have retained its age information. Also, presumably Theia didn’t bounce off but just merged with the moon being formed from the piece of Earth on the opposite side from the collision that got ejected, right? So at most half the moon surface should be from the collision and half of it should have the age of the Earth?
- treeman79 5y ago
  Moon is a mix of earth and theia. So is Earth. So sort of like a strawberry banana smoothie in two cups. Core of Theia sunk into Earth and there is some recent imaging showing what may be the second core. https://www.iflscience.com/environment/fragments-of-the-planet-that-formed-the-moon-may-be-buried-by-the-earths-core/ https://www.iflscience.com/environment/fragments-of-the-plan...
  - jacquesm 5y ago
    Theia is - for now - a hypothesis, not an established fact.
sokoloff 5y ago
That led me down a “how did they date the moon rocks?” thread, which led me to this explanation: https://www.sciencealert.com/we-finally-know-the-precise-age-of-the-moon-thanks-to-apollo-14-moon-rocks https://www.sciencealert.com/we-finally-know-the-precise-age...
- 37 5y ago
  >researchers say they’ve finally pinpointed the exact age of the Moon Hmm, sounds dubious, but I will read on. A short while later it leads me to the paper[0] and I spend a few more minutes on that, finding myself asking: how do we know the zircon fragments aren't from a meteor that is much older? Surely all the fragments came from approximately the same area, yes? Or maybe not? But nah, these knowledgeable astronomers must have already thought of all this stuff. Astronomy is just filled with rabbit holes I guess. [0] https://www.science.org/doi/10.1126/sciadv.1602365 https://www.science.org/doi/10.1126/sciadv.1602365
  - kfarr 5y ago
    Just wait until you hear how astronomers date the approximate age of rabbit holes…
  - pdonis 5y ago
    > how do we know the zircon fragments aren't from a meteor that is much older? Radiometric dating tells you when the sample you are dating last solidified. Of course the atoms in the sample themselves existed before that, but that doesn't matter for radiometric dating since what is being measured is not the age of the atoms but the time the sample, the piece of rock you're analyzing, last solidified. > Surely all the fragments came from approximately the same area, yes? Um, yes, since the Apollo 14 astronauts only collected samples from a very small area. > nah, these knowledgeable astronomers must have already thought of all this stuff. Yes, in fact, they have, plus a lot more things that haven't even occurred to you.
    - jacquesm 5y ago
      > Yes, in fact, they have, plus a lot more things that haven't even occurred to you. Exactly. Like that comment about the JWST last week that was wondering why they didn't bring down the number of single-points-of-failure. Backseat driving at its best.

by 37 5y ago

politician 5y ago

Isn't it kind of weird to use the Moon to benchmark the age of the solar system when it's well known that the Moon formed after another body collided with the Earth? The Moon is younger than the Earth.

tshaddox 5y ago
I assume it’s because the Moon is geologically inactive and thus the rocks we got from the surface are expected to be essentially as old as the Moon itself.
pdonis 5y ago
Not to benchmark, precisely, but to give a lower limit on the age that will likely be longer than any other lower limit we could obtain at our current or near future level of technology.
vlovich123 5y ago
If Theia is older than the Earth, then wouldn't the Moon also be older?
- politician 5y ago
  AIUI, the heat of the collision would've melted everything that wasn't already molten. Any "age" information would be lost as the system cooled. At least, that's my understanding from playing with Universe Sandbox.
  - vlovich123 5y ago
    That would only be the case for the piece that collided though right? The side that wasn’t part of the collision should have retained its age information. Also, presumably Theia didn’t bounce off but just merged with the moon being formed from the piece of Earth on the opposite side from the collision that got ejected, right? So at most half the moon surface should be from the collision and half of it should have the age of the Earth?
treeman79 5y ago
Moon is a mix of earth and theia. So is Earth. So sort of like a strawberry banana smoothie in two cups. Core of Theia sunk into Earth and there is some recent imaging showing what may be the second core. https://www.iflscience.com/environment/fragments-of-the-planet-that-formed-the-moon-may-be-buried-by-the-earths-core/ https://www.iflscience.com/environment/fragments-of-the-plan...
- jacquesm 5y ago
  Theia is - for now - a hypothesis, not an established fact.

sokoloff 5y ago

That led me down a “how did they date the moon rocks?” thread, which led me to this explanation: https://www.sciencealert.com/we-finally-know-the-precise-age-of-the-moon-thanks-to-apollo-14-moon-rocks https://www.sciencealert.com/we-finally-know-the-precise-age...

37 5y ago
>researchers say they’ve finally pinpointed the exact age of the Moon Hmm, sounds dubious, but I will read on. A short while later it leads me to the paper[0] and I spend a few more minutes on that, finding myself asking: how do we know the zircon fragments aren't from a meteor that is much older? Surely all the fragments came from approximately the same area, yes? Or maybe not? But nah, these knowledgeable astronomers must have already thought of all this stuff. Astronomy is just filled with rabbit holes I guess. [0] https://www.science.org/doi/10.1126/sciadv.1602365 https://www.science.org/doi/10.1126/sciadv.1602365
- kfarr 5y ago
  Just wait until you hear how astronomers date the approximate age of rabbit holes…
- pdonis 5y ago
  > how do we know the zircon fragments aren't from a meteor that is much older? Radiometric dating tells you when the sample you are dating last solidified. Of course the atoms in the sample themselves existed before that, but that doesn't matter for radiometric dating since what is being measured is not the age of the atoms but the time the sample, the piece of rock you're analyzing, last solidified. > Surely all the fragments came from approximately the same area, yes? Um, yes, since the Apollo 14 astronauts only collected samples from a very small area. > nah, these knowledgeable astronomers must have already thought of all this stuff. Yes, in fact, they have, plus a lot more things that haven't even occurred to you.
  - jacquesm 5y ago
    > Yes, in fact, they have, plus a lot more things that haven't even occurred to you. Exactly. Like that comment about the JWST last week that was wondering why they didn't bring down the number of single-points-of-failure. Backseat driving at its best.