Question

Cosmic rays knock neutrons out of atomic nuclei in the upper atmosphere. Displaced neutrons hit ordinary nitrogen (14N) at lower altitudes, converting it into 14C. Unlike common carbon (12C), 14C is unstable and slowly decays, changing it back to nitrogen and releasing energy (radioactivity). Living organisms turn atmospheric carbon into tissue with the same ratio 14C/ 12C as in the atmosphere (1 in a trillion). How is this process utilized to determine the age of organic items that are less than 30,000 years old? A. When organism dies, 12C remains, but 14C decays with a half-life of 5730 years B. 14C gives off X-rays which can be tracked with a Geiger counter C. The amount of 14C in the atmosphere has been steadily decreasing at a known rate for 30,000 years so we can compare 12C / 14C ratios to determine the age D. 12C as present in carbon dioxide gas is more volatile that 14C present in carbon dioxide gas so we can look at the isotope ratios in carbon dioxide gas within the item we are dating

Answer 1

Solution:

The correct answer is A. When organism dies, 12C remains, but 14C decays with a half-life of 5730 years .

Explanation:

For carbon dating, the amount of Carbon-14 (radioactive form) is compared to the amount of Carbon-12 (the stable form ) to determine how much radiocarbon has decayed. At any particular time all living organisms have approximately the same ratio of carbon 12 to carbon 14 in their tissues. When an organism dies it ceases to replenish carbon in its tissues and the decay of carbon 14 to nitrogen 14 changes the ratio of carbon 12 to carbon 14. The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of oraganic items which are less than 30,000 years old.