The age of fossils can be estimated now by

Options

A. earth's crust
B. amount of calcium deposited
C. remaining quantity of radioactive carbon in relevant rocks
D. All of the above

Answer

**Step-by-Step Solution:**

1. **Understanding Fossil Age Estimation**: The age of fossils is crucial for understanding the history of life on Earth. Scientists have developed methods to estimate how old these fossils are.

2. **Introduction to Carbon Dating**: One of the most widely used methods for estimating the age of fossils is known as carbon dating. This technique is based on the principles of radioactive decay.

3. **Radioactive Carbon Isotope**: The specific isotope of carbon used in this method is Carbon-14 (C-14). This isotope is radioactive and decays over time.

4. **Decay Process**: When an organism dies, it stops taking in Carbon-14. The Carbon-14 that is present in its tissues begins to decay at a known rate (its half-life is about 5,730 years). By measuring the remaining amount of Carbon-14 in the fossil, scientists can estimate how long it has been since the organism died.

5. **Application of Carbon Dating**: This method is particularly effective for dating organic materials that are up to about 50,000 years old. It is commonly used in archaeology and geology to date ancient remains.

6. **Conclusion**: Therefore, the age of fossils can be estimated by measuring the remaining quantity of radioactive carbon (C-14) in the relevant rocks or organic materials associated with the fossils.

**Final Answer**: The age of fossils can be estimated now by the remaining quantity of radioactive carbon in relevant rocks.

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