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Author Topic:   The dating game
Posts: 5552
From: Snyder, Texas, USA
Joined: 11-12-2002

Message 15 of 94 (392672)
04-01-2007 6:26 PM
Reply to: Message 1 by Reserve
03-31-2007 2:11 PM

Hi, Reserve! Welcome!

It says that Potasium-argon does not work for recent dates. I wonder, why not? why only for ages older than 100kya? Radioactivity is a recently discovered tool from around the 19th century which is about 200 years ago.

That first part is nearly true, but there's a variation of potassium-argon dating, called argon-argon, that's been used to date the Pompeii-burying eruption of Vesuvius. That was in 79AD, by historical and tree-ring dates, and argon-argon got it right with an error of +/- 94 years. There, but you must register for free to read it.

Here's the abstract:

Laser incremental heating of sanidine from the pumice deposited by the Plinian eruption of Vesuvius in 79 A.D. yielded a 40Ar/39Ar isochron age of 1925 ± 94 years ago. Close agreement with the Gregorian calendar-based age of 1918 years ago demonstrates that the 40Ar/39Ar method can be reliably extended into the temporal range of recorded history. Excess 40Ar is present in the sanidine in concentrations that would cause significant errors if ignored in dating Holocene samples.

This message is a reply to:
 Message 1 by Reserve, posted 03-31-2007 2:11 PM Reserve has not yet responded

Posts: 5552
From: Snyder, Texas, USA
Joined: 11-12-2002

Message 28 of 94 (392835)
04-02-2007 2:53 PM
Reply to: Message 25 by Reserve
04-02-2007 12:40 PM

Re: No mystery
(Dalrymple GB, Moore JG: Science 1968;161:1132-5)

39 years old, and the abstract says

Submarine pillow basalts from Kilauea Volcano contain excess radiogenic argon-40 and give anomalously high potassium-argon ages. Glassy rims of pillows show a systematic increase in radiogenic argon-40 with depth, and a pillow from a depth of 2590 meters shows a decrease in radiogenic argon40 inward from the pillow rim. The data indicate that the amount of excess radiogenic argon-40 is a direct function of both hydrostatic pressure and rate of cooling, and that many submarine basalts are not suitable for potassium-argon dating.
(my emphasis)

Noble CS, Naughton JJ: Science 1968;162:265-7

39 years old, and the title says
Deep-Ocean Basalts: Inert Gas Content and Uncertainties in Age Dating

Reserve, do you think the authors were complete morons, or perhaps is it your source being less than forthright with what they know?

This message is a reply to:
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Replies to this message:
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Posts: 5552
From: Snyder, Texas, USA
Joined: 11-12-2002

Message 88 of 94 (642764)
12-01-2011 11:05 AM
Reply to: Message 87 by Pollux
12-01-2011 7:21 AM

Technetium is present in some Red Giant stars that are actively dredging up material from their interiors - where fresh technetium is being synthesized by nuclear reactions. Googling "solar technetium" turns up some very old references that raise the possibility of some in the Sun, but more, later references that say probably the spectral lines are misassigned. The Moon doesn't seem to have any.

Some Cretinists claim the the "accelerated nuclear decay" was during their Creation Week - so they will just say that the Sun and Moon were made without Tc or were subject to accelerated decay as well.

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