Fossils are dated by

Options

A. Amount of calcium residue in them
B. Their sodium content
C. Their number in an area.
D. Amount of radioactive carbon isotope in them

Answer

**Step-by-Step Solution:**

1. **Understanding Fossil Dating**: Fossil dating refers to the methods used to determine the age of fossils. This is crucial in understanding the timeline of life on Earth and the evolution of species.

2. **Identifying Methods of Dating**: There are several methods to date fossils, including relative dating and absolute dating. Absolute dating provides a more precise age.

3. **Carbon Dating**: The most commonly used method for absolute dating of fossils is Carbon-14 dating. This technique measures the amount of radioactive carbon isotope (C-14) present in organic materials.

4. **Radioactive Isotopes**: Carbon-14 is a radioactive isotope that decays over time. By measuring the remaining C-14 in a fossil, scientists can calculate how long it has been since the organism died.

5. **Conclusion**: Based on the above information, the correct option for how fossils are dated is the "amount of radioactive carbon isotope in them."

**Final Answer**: The fossils are dated by the amount of radioactive carbon isotope in them (Option D).

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