Age of fossils in the past was generally determined by radiocarbon method and other methods involving radioactive elements found in the rocks. More precise methods, which were used recently and led to the revision of the evolutionary periods for different groups of organisms, includes

Options

A. Study of carbohydrates proteins in fossils
B. Study of the condiitions of fossilization.
C. Electron spin resonance and fossil
D. Study of carbohydrates / proteins in rocks.

Answer

To answer the question regarding the more precise methods used recently for determining the age of fossils, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding Fossil Dating**: Fossils were traditionally dated using methods like radiocarbon dating, which relies on the decay of radioactive isotopes such as carbon-14. This method is effective for relatively recent fossils (up to about 50,000 years).

2. **Need for More Precise Methods**: As the field of paleontology evolved, scientists recognized the need for more precise dating methods to revise the evolutionary timelines of various organisms. This is particularly important for older fossils, where radiocarbon dating is not applicable.

3. **Introduction of Electron Spin Resonance (ESR)**: One of the more recent and precise methods developed is Electron Spin Resonance (ESR), also known as Electron Paramagnetic Resonance (EPR). This technique measures the unpaired electrons in the crystal structure of minerals found in fossils.

4. **Mechanism of ESR**: In ESR, scientists analyze the number of unpaired spins of electrons that are trapped in the mineral lattice of the fossil. This allows for dating of materials that are much older than those that can be dated by radiocarbon methods.

5. **Applications of ESR**: ESR has been successfully used to date coral reefs and tooth enamel, providing more accurate age estimates for these materials compared to traditional methods.

6. **Conclusion**: Therefore, the more precise methods that have been used recently to revise the evolutionary periods for different groups of organisms include Electron Spin Resonance and fossil DNA analysis.

### Final Answer:
The more precise methods recently used for determining the age of fossils include **Electron Spin Resonance (ESR)** and **fossil DNA analysis**.

---