
Scientists Find Record 2.7M-Year-Old Ice Core in Antarctica - Mz
http://www.smithsonianmag.com/smart-news/scientists-find-27-million-year-old-ice-core-antarctica-180964566/?no-ist
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greglindahl
This appears to be how they computed the date:
[https://en.wikipedia.org/wiki/K%E2%80%93Ar_dating](https://en.wikipedia.org/wiki/K%E2%80%93Ar_dating)

With just 1 sample they can't conclude much, but if they find a bunch of
others, they'll have an interesting set of datapoints from the composition of
the tiny air pockets in the ice.

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llccbb
You can read more in this open-access PNAS article[0].

[0][http://www.pnas.org/content/105/24/8232.full](http://www.pnas.org/content/105/24/8232.full)

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EGreg
Does this mean it should have 2.7 million ice core layers in the cross
section?

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diggernet
Apparently not. They say the ice "is not organized into neat layers", so they
have approximated the age based on potassium and argon concentration.

Though it doesn't mention what potassium and argon have to do with age. Short
explanation, anyone?

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sir_kitty
Isotopes of potassium decay to argon and the amount of accumulated argon -
combined with knowledge of the decay rate - allows one to use the system as a
clock:

[https://en.wikipedia.org/wiki/K%E2%80%93Ar_dating](https://en.wikipedia.org/wiki/K%E2%80%93Ar_dating)

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jhawk28
that assumes you know how much it started with and what the environment was
like then

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greglindahl
The Wikipedia page covers these issues, albeit for crystalized rock instead of
ice. The measurement is a ratio, so the key thing is establishing that Argon
40 is normally not present in rain or brand new ice.

