Question

In living things, what is the source of the carbon-14 that is used in radiocarbon dating?

A. Carbon dioxide in rocks
B. Carbonic acid in caves
C. Carbon dioxide in the atmosphere
D. Carbon dioxide in water

Answer 1

"The primary natural source of carbon-14 on Earth is cosmic ray action on nitrogen in the atmosphere, and it is therefore a cosmogenic nuclide."
Carbon-14 - Wikipedia

Answer 2

Isn't Wikipedia untrustworthy??

Answer 3

No. I would, of course, get other opinions on a controversial subject -- but Wikipedia is right on scientific and historical questions. No one has any motivation to change anything that is not controversial.

However -- feel free to use another source.

Answer 4

Give me six water, six carbon dioxide. . . I take that and look what I do on the inside. Sunlight as my engine, I can’t wait to taste The glucose I make, chuck six oxygen as waste. I’m the chloroplast. Photosynthesis is my task. It’s a blast and I’m jazzed. Why’d I tell you? ‘cause you asked