copy of 5e.carbon dating 5

8/14/2019 Copy of 5e.carbon Dating 5

1/9

Carbon Dating...HowCarbon Dating...How

accurate are scientistsaccurate are scientistswhen estimating the agewhen estimating the age

of the earth?of the earth?


2/9

Proposed Explanation OfProp

osed Explanation Of

EvolutionEvolution

Fossils preserved in rock strata provide scientistswith clues to evolutionary history. This stratigraphiccolumn is based on paleontological evidence, and

shows the order in which organisms appeared in thefossil-rich Paleozoic Era. Each layer represents aparticular time frame and shows a representativeorganism which flourished during that time. Althoughfossils are rarely found in the idealized and localized

fashion shown here, they are often in more or lesschronological order. Generally, the oldest fossilsappear in lower layers, and the most recent fossils atthe top, so that placement may be used as an aid indating the specimens.


3/9

Radio-Carbon Dating (C-14)Radio-Carbon Dating

(C-14)

All living organisms absorb radiocarbon, an unstable form of carbon thathas a half-life of about 5,730 years. During its lifetime, an organism

continually replenishes its supply of radiocarbon by breathing and eating.After the organism dies and becomes a fossil, C-14 continues to decaywithout being replaced. To measure the amount of radiocarbon left in afossil, scientists burn a small piece to convert it into carbon dioxide gas.Radiation counters are used to detect the electrons given off by decayingC-14 as it turns into nitrogen. The amount of C-14 is compared to theamount of C-12, the stable form of carbon, to determine how much

radiocarbon has decayed and to date the fossil.


4/9

Carbon MoleculesCarbon Molecules

Carbon has three naturallyCarbon has three naturallyoccurring isotopes: carbon-12occurring isotopes: carbon-12constitutes 98.89 percent of allconstitutes 98.89 percent of allcarbon atoms and serves as thecarbon atoms and serves as thestandard for the atomic massstandard for the atomic massscale; carbon-13 is the onlyscale; carbon-13 is the onlymagnetic isotope, which makesmagnetic isotope, which makes

it very important for structuralit very important for structuralstudies of compoundsstudies of compoundscontaining carbon. Carbon-14 iscontaining carbon. Carbon-14 isproduced by cosmic rayproduced by cosmic raybombardment of nitrogen. It isbombardment of nitrogen. It isradioactive with a half-life ofradioactive with a half-life of5,760 years. The amount of5,760 years. The amount of

carbon-14 remaining incarbon-14 remaining inhistorical artifacts can be usedhistorical artifacts can be usedtoto estimateestimate their age.their age. Microsoft MicrosoftEncartaEncarta


5/9

Carbon, used by all living organisms, continuously circulates in theearths ecosystem. In the atmosphere, it exists as colorless, odorless

carbon dioxide gas, which is used by plants in the process ofphotosynthesis. Animals acquire the carbon stored in plant tissue when

they eat and exhale carbon dioxide as a by-product of metabolism.Although some carbon is removed from circulation temporarily as coal,petroleum, fossil fuels, gas, and limestone deposits, respiration andphotosynthesis balance to keep the amount of atmospheric carbon

relatively stable. Industrialization, however, has contributed additionalcarbon dioxide to the environment.

- Microsoft Encarta


6/9

The Half-Life ProblemThe Half-Life Problem Here's an example of how half-life works:Here's an example of how half-life works:

Let's say you have 80 ants, and these antsLet's say you have 80 ants, and these antshave a half-life of ten days. In ten days, then,have a half-life of ten days. In ten days, then,40 of your ants would still be alive. Ten days40 of your ants would still be alive. Ten daysafter that, 20 ants would still be alive. Tenafter that, 20 ants would still be alive. Tenmore days, and ten would be alive. You getmore days, and ten would be alive. You get

the picture.the picture.If you took just one of these ants, though,If you took just one of these ants, though,there would be no way to predict when itthere would be no way to predict when it

would die. It might die right away or it mightwould die. It might die right away or it mightlive for a long time. It's only when you have alive for a long time. It's only when you have a

lot of them that this half-life thing works.lot of them that this half-life thing works.In real life, you can't use the half-life methodIn real life, you can't use the half-life method

to determine ant death rates. You can,to determine ant death rates. You can,however, use the method to determine whenhowever, use the method to determine whenradioactive atoms will decay into some otherradioactive atoms will decay into some other

form.form. Half-lives vary greatly from one radioactiveHalf-lives vary greatly from one radioactive

atom to another. The reason is that a highlyatom to another. The reason is that a highlyunstable atom wants to change quickly,unstable atom wants to change quickly,

whereas a slightly unstable atom is onlywhereas a slightly unstable atom is onlyslightly uncomfortable with its condition. Theslightly uncomfortable with its condition. Thehalf-life of highly unstable radon-222 is lesshalf-life of highly unstable radon-222 is lessthan four days. The half-life of the slightlythan four days. The half-life of the slightlyunstable uranium-238 is 4.5 billion years.unstable uranium-238 is 4.5 billion years.Carbon-14 has a half-life of 5,730 years.Carbon-14 has a half-life of 5,730 years.


7/9

Other ProblemsOther Problems

The Magnetic ProblemThe Magnetic Problem


8/9

Fossil DatingFossil Dating

Levels of C-14 in fossilsLevels of C-14 in fossilsare so low that datingare so low that dating

them is virtuallythem is virtuallyimpossible. Why are C-impossible. Why are C-

14 levels so low?14 levels so low?


9/9

Carbon Dating.impossible?Carbon Dating.impossible?

copy of 5e.carbon dating 5

Documents