Mass extinction of species has occurred during

Options

A. KT Boundary
B. Pleistocene
C. Permian
D. All of the above

Answer

### Step-by-Step Solution:

1. **Define Mass Extinction**:
- Mass extinction refers to a rapid and widespread decrease in the biodiversity on Earth, where a significant number of species, both plants and animals, become extinct in a relatively short period of geological time.

2. **Identify Major Mass Extinction Events**:
- There have been several major mass extinction events throughout Earth's history. Some of the most notable ones include:
- Ordovician-Silurian (440 million years ago)
- Late Devonian (365 million years ago)
- Permian-Triassic (250 million years ago)
- Triassic-Jurassic (210 million years ago)
- Cretaceous-Paleogene (65 million years ago)
- Pleistocene (11,000 years ago)

3. **Review the Options Provided**:
- The question provides different time periods as options. We need to determine which of these periods are associated with mass extinction events.

4. **Analyze Each Time Period**:
- **Cretaceous-Tertiary (KT Boundary)**: This period is known for the mass extinction that led to the demise of the dinosaurs and about 75% of Earth's species.
- **Pleistocene**: This period saw the extinction of many large mammals, such as mammoths and saber-toothed cats.
- **Permian**: This is known as the Great Dying, where approximately 95% of marine species and many terrestrial species went extinct.

5. **Conclusion**:
- Since all the options provided (KT boundary, Pleistocene, and Permian) correspond to significant mass extinction events, the correct answer is "All of the above".

### Final Answer:
- The mass extinction of species has occurred during various time periods, specifically including the Cretaceous-Tertiary, Pleistocene, and Permian periods. Therefore, the answer is "All of the above".