Answer to Question #289695 in Civil and Environmental Engineering for Topher

Question

Radiocarbon Dating Analysis

Radiocarbon dating analysis is a technique used by archeologists and paleonto-

logists to determine the approximate age of an organic sample. It uses C-14/

C-12 ratios to determine the time that has elapsed since a living organism has

died.

a. What is the idea behind this technique? Explain this process. Use illustrations.

b. How is the C-14/C-12 ratio of samples measured?

c. Will radiocarbon dating analysis work for metallic artifacts? What are your

reasons behind your response?

d. Suppose a piece of cloth was found to contain a third of its original C-14/C12

ratio, what is the approximate age of the sample? State any assumptions you

made during calculation.

Answer 1

Nothing good can last—and in the case of carbon-14, a radioactive isotope found in Earth’s atmosphere, that’s great news for archaeologists.

Over time, carbon-14 decays in predictable ways. And with the help of radiocarbon dating, researchers can use that decay as a kind of clock that allows them to peer into the past and determine absolute dates for everything from wood to food, pollen, poop, and even dead animals and humans.

Counting carbon

While plants are alive, they take in carbon through photosynthesis. Humans and other animals ingest the carbon through plant-based foods or by eating other animals that eat plants. Carbon is made up of three isotopes. The most abundant, carbon-12, remains stable in the atmosphere. On the other hand, carbon-14 is radioactive and decays into nitrogen-14 over time. Every 5,730 years, the radioactivity of carbon-14 decays by half.

That half-life is critical to radiocarbon dating. Since carbon-12 doesn’t decay, it’s a good benchmark against which to measure carbon-14’s inevitable demise. The less radioactivity a carbon-14 isotope emits, the older it is. And since animals and plants stop absorbing carbon-14 when they begin to decay, the radioactivity of the carbon-14 that’s left behind reveals their age.

There’s a catch: Atmospheric carbon fluctuates over time. But the amount of carbon-14 in tree rings with known ages can help scientists correct for those fluctuations. To date an object, researchers use mass spectrometers or other instruments to determine the ratio of carbon-14 and carbon-12. The result is then calibrated and presented.