K-T boundary is characterised by the presence of

Options

A. Iridium
B. Gold
C. Avian fossile
D. Petroleum

Answer

To answer the question about what characterizes the K-T boundary, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the K-T Boundary**: The K-T boundary, also known as the Cretaceous-Tertiary boundary, is a geological marker that separates the Cretaceous period from the Tertiary period. It is significant in the study of Earth's history, particularly concerning mass extinctions.

2. **Identifying the Key Characteristics**: The K-T boundary is known for specific geological and chemical signatures that indicate a major event in Earth's history, particularly the mass extinction event that led to the demise of the dinosaurs.

3. **Researching the Elements Found**: Among the various elements and minerals studied at the K-T boundary, one of the most notable is iridium. Iridium is a rare element on Earth's surface but is more abundant in asteroids and comets.

4. **Historical Discovery**: The presence of iridium at the K-T boundary was notably studied by scientists Lewis and Walter Alvarez. They discovered that the concentration of iridium in this layer was significantly higher than what is typically found in Earth's crust.

5. **Conclusion**: Based on the evidence and research, the K-T boundary is characterized by the presence of iridium, which is believed to have been deposited by an asteroid impact that contributed to the mass extinction event.

### Final Answer:
The K-T boundary is characterized by the presence of **A. Iridium**.

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