Freethought & Rationalism Archive

ishalon · 06-14-2002, 08:16 AM

Quote:

Give this person a Nobel prize! I bet you're going to tell us about all these sea creatures (the mollusck shell one is a favourite among the scientifically illiterate) that have been dated wrongly with carbon dating. Carbon dating does not apply to sea creatures, who do not have the same carbon cycle as land creatures, where it does apply. Please read a book about how carbon dating works, you are desperately in the need of an education. And this was known before the sea creature "disproofs" were reported, because it is based on C-14 forming in the upper atmosphere via cosmic irradiation then being absorbed by trees and continuing on the terrestrial carbon cycle, which has little to nothing to do with the sea environment.

Is this true? I don't see the difference with being absorbed by trees and being absorbed by seaweed, plankton and anything else with chloroplasts. What makes it not work on sea creatures?

Coragyps · 06-14-2002, 09:16 AM

Ishalon: 14C dating doesn't work "properly" on many aquatic critters for a couple of reasons. First, the dissolved carbon (in the form of bicarbonate, mostly) in the oceans is not terribly "new." It's been in solution for some hundreds of years, circulating down to the deeps and back up again. The carbon-14 in this bicarbonate came from carbon dioxide in the atmosphere, but it has been decaying while in the water and so appears "old."

This same sort of thing can be seen elsewhere, too. One paper from Science that is cited by creationists as "debunking" 14C dating is actually an early (1970? I may have it at home) study on when you can't believe 14C dates. Living snails in a pond in Nevada were dated as thousands of years old - the water they lived in was from a spring that was fed from a big aquifer, and all the bicarbonate in that water was thousands of years old. Its 14C had all decayed, and the snail apparent age was from the mixture of it with "young" atmospheric CO2.

One other cause for bad ages that I have heard of is that some aquatic organisms ingest, or metabolize, some amount of limestone, which can be ancient and so devoid of 14C.

ishalon · 06-14-2002, 09:40 AM

thanks alot, but to the last sentence, whats the maximum- carbon- date?

and how do we know some million-year old fossil didnt eat limestone for 1 reason or the other?

Coragyps · 06-14-2002, 09:58 AM

Carbon 14 has a half-life of about 5700 years, so only one part in 1,024 is left after 57,000 years = ten half-lives. About 50,000 years is the maximum that it can be used for, though technology may be able to push that back a bit. Other methods, like rubidium/strontium, must be used for million-year ages.

brighid · 06-14-2002, 10:08 AM

Quote:

Although little is known about this sinister organization, it is believed that "Cabal" is a euphemism for the Vast Worldwide Evilutionist Conspiracy which seeks to undermine the morality, sovreignty and freedom of the United States through a coordinated campaign of intimidation, propaganda, and falsehood directed at brainwashing the youth of the nation. The VWEC is trying to force the world to accept its long-dicredited religious dogma known as the "Theory of Evolution". Allegedly, tens of thousands of scientists from around the world are involved in this effort.

Change a few words around and you have the description of the Christian Right in America.

B

ishalon · 06-14-2002, 10:37 AM

i c... so since im asking endless questions, whats the maximum dating we can do?

scigirl · 06-14-2002, 11:44 AM

Quote:

Originally posted by ishalon:
<strong>i c... so since im asking endless questions, whats the maximum dating we can do?</strong>

Oh, you must have discoverd infidel chat!

There must be some good educational links about this subject. . . <a href="http://gened.emc.maricopa.edu/bio/bio181/BIOBK/BioBookPaleo1.html" target="_blank">Try this on-line bio book for "simple" explanations.</a>

scigirl

Corwin · 06-14-2002, 11:45 AM

Depends on the element used. C14 only works back to around fifty thousand years... (and a lot of people don't like to use it much past thirty thousand... it depends on how precise their instruments are.) If you go into the transuranics, (uranium and thorium for example) or potassium-argon dating, it can go back millions of years.

Skydancer · 06-14-2002, 12:02 PM

Quote:

Originally posted by Corwin:
<strong>Depends on the element used. C14 only works back to around fifty thousand years... (and a lot of people don't like to use it much past thirty thousand... it depends on how precise their instruments are.) If you go into the transuranics, (uranium and thorium for example) or potassium-argon dating, it can go back millions of years.</strong>

Billions. K-Ar and uranium/thorium are hard to work with at any scale less than a few dozen million years.... so there's an annoying gap in there for the 100,000 to 10,000,000 year range. The maximum age we've ever found is about 4 and 1/2 billion years, which appears to be the age of the solar system.

lpetrich · 06-14-2002, 12:15 PM

Some radioactive elements often used in radiometric dating, their stable decay products, and their half-lives:

Potassium-40 -> Argon-40 (1.25 billion years)
Rubidium-87 -> Strontium-87 (48.8 billion years)
Thorium-232 -> Lead-208 (14 billion years)
Uranium-235 -> Lead-207 (0.704 billion years)
Uranium-238 -> Lead-206 (4.47 billion years)
Carbon-14 -> Nitrogen-14 (5730 years)

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06-14-2002, 09:16 AM	#62
Coragyps Veteran Join Date: Aug 2001 Location: Snyder,Texas,USA Posts: 4,411	Ishalon: 14C dating doesn't work "properly" on many aquatic critters for a couple of reasons. First, the dissolved carbon (in the form of bicarbonate, mostly) in the oceans is not terribly "new." It's been in solution for some hundreds of years, circulating down to the deeps and back up again. The carbon-14 in this bicarbonate came from carbon dioxide in the atmosphere, but it has been decaying while in the water and so appears "old." This same sort of thing can be seen elsewhere, too. One paper from Science that is cited by creationists as "debunking" 14C dating is actually an early (1970? I may have it at home) study on when you can't believe 14C dates. Living snails in a pond in Nevada were dated as thousands of years old - the water they lived in was from a spring that was fed from a big aquifer, and all the bicarbonate in that water was thousands of years old. Its 14C had all decayed, and the snail apparent age was from the mixture of it with "young" atmospheric CO2. One other cause for bad ages that I have heard of is that some aquatic organisms ingest, or metabolize, some amount of limestone, which can be ancient and so devoid of 14C.

06-14-2002, 09:40 AM	#63
ishalon Regular Member Join Date: May 2002 Location: From: Posts: 203	thanks alot, but to the last sentence, whats the maximum- carbon- date? and how do we know some million-year old fossil didnt eat limestone for 1 reason or the other?

06-14-2002, 09:58 AM	#64
Coragyps Veteran Join Date: Aug 2001 Location: Snyder,Texas,USA Posts: 4,411	Carbon 14 has a half-life of about 5700 years, so only one part in 1,024 is left after 57,000 years = ten half-lives. About 50,000 years is the maximum that it can be used for, though technology may be able to push that back a bit. Other methods, like rubidium/strontium, must be used for million-year ages.

06-14-2002, 10:37 AM	#66
ishalon Regular Member Join Date: May 2002 Location: From: Posts: 203	i c... so since im asking endless questions, whats the maximum dating we can do?

06-14-2002, 11:45 AM	#68
Corwin Veteran Member Join Date: Jan 2002 Posts: 4,369	Depends on the element used. C14 only works back to around fifty thousand years... (and a lot of people don't like to use it much past thirty thousand... it depends on how precise their instruments are.) If you go into the transuranics, (uranium and thorium for example) or potassium-argon dating, it can go back millions of years.

06-14-2002, 12:15 PM	#70
lpetrich Contributor Join Date: Jul 2000 Location: Lebanon, OR, USA Posts: 16,829	Some radioactive elements often used in radiometric dating, their stable decay products, and their half-lives: Potassium-40 -> Argon-40 (1.25 billion years) Rubidium-87 -> Strontium-87 (48.8 billion years) Thorium-232 -> Lead-208 (14 billion years) Uranium-235 -> Lead-207 (0.704 billion years) Uranium-238 -> Lead-206 (4.47 billion years) Carbon-14 -> Nitrogen-14 (5730 years)

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