Radiokoolstofdatering - Wikipedia
Radiokoolstofdatering, of koolstof 14-datering, word algemeen deur veral argeoloë gebruik om die ouderdom van voorwerpe te bepaal wat jonger as 50 000 jaar is (laat-Kwartêr en Holoseen), en koolstof in hulle samestelling bevat. Hierdie voorwerpe sluit houtskool, hout, been, stuifmeel, skulpe, grondwater en kalkreet in.
Daar bestaan ’n algemene wanopvatting dat koolstof 14-datering gebruik kan word om die ouderdom van die aarde te bepaal. Dit is egter onmoontlik aangesien die halfleeftyd van die koolstof-14 (14C)-isotoop net sowat 5 715 jaar is, en dus slegs geskik is om ouderdomme van sowat 50 000 jaar of minder te bepaal. Radiodateringsmetodes waarmee geologiese tyd gemeet kan word, sluit uraan-lood (U/Pb)-, kalium-argon (K/Ar)- en rubidium-stronsium ( Rb/Sr)-radiodatering in. Hierdie tegnieke is geskik vanweë die baie lang halfleeftyd van die moederelemente.
Koolstof het twee stabiele isotope wat natuurlik voorkom: koolstof 12 (12C; 98,89%) en koolstof 13 (13C; 1,11%), asook ’n onstabiele isotoop, koolstof 14. Laasgenoemde is van groot belang, aangesien die onstabiele aard daarvan radiokoolstofdatering moontlik maak.
Koolstof 14 het ’n halfleeftyd van 5 715 jaar en word gevorm deur kosmiese strale wat stikstof 14-isotope in die boonste atmosfeer verander in 14C-isotope. Hierdie nuut gevormde isotope word gaandeweg in die atmosferiese CO2 opgeneem.
Vanweë die voortdurende vorming van die 14C-isotoop bly die verhouding tussen 14C en 12C redelik konstant. Hierdie verhouding bestaan ook in die CO2 wat deur plante, skulpe, diere en gesteentes opgeneem word. Wanneer die organisme doodgaan, hou dit op om koolstofdioksied CO2 (en dus 14C) op te neem. Die koolstof 14 wat voor die organisme se dood opgeneem is, verminder gaandeweg namate dit weer as gevolg van radioaktiewe verval in stikstof 14 verander. Wanneer ’n monster van die material (hout, been, skulpe ens.) in ’n laboratorium ontleed word, word die 14C /12C-verhouding bepaal en met die atmosferiese verhouding vergelyk.
Aangesien die tempo van radioaktiewe verval bekend is en die atmosferiese verhouding redelik konstant bly, is die hoeveelheid 14C wat verdwyn het relatief tot die oorblywende 12C ’n aanduiding van die ouderdom van die monster.
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RADON – database for European 14C dates
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Last edited on 20 November 2017, at 04:05