The age of a fossil is estimated by measuring radioactivity and the ratio of which isotope to C-12?

1. While alive, an organism keeps taking in carbon, so its C-14 level stays steady. 2. After death, carbon intake stops and the radioactive C-14 begins to decay. 3. C-12 is non-radioactive, so it stays constant in the dead body. 4. Therefore the C-14 to C-12 ratio falls steadily after death. 5. Measuring C-14 radioactivity and this ratio gives the fossil's age, called carbon dating. 6. So the isotope compared with C-12 is C-14. 7. Trap (O-16): oxygen-16 is stable and not used for this dating. 8. Trap (N-14): nitrogen-14 is the decay product, not the measured ratio against C-12. 9. Trap (H-1): hydrogen-1 plays no role in carbon dating. _Source: Balbharati (Maharashtra Board) Class 10 Science & Technology Part 2, Ch 1 "Heredity and Evolution", p.15_