Question

Which one of the following features is used to define the K-Pg boundary globally?

• A. Absence of dinosaur fossils
• B. Presence of iridium anomaly in sediments
• C. Presence of high mercury content in sediments
• D. End of Deccan volcanism

Hint:

The iridium anomaly at the K-Pg boundary is a critical marker for the mass extinction event caused by the asteroid impact.

Answer 1

The Correct Option is B

Step 1: Understanding the K-Pg boundary.
The K-Pg boundary marks the end of the Cretaceous period and the beginning of the Paleogene period. It is most famously associated with the mass extinction event that led to the demise of the dinosaurs and many other species.
The boundary is globally recognized based on specific geological features found in the stratigraphic record.

Step 2: Analyzing the iridium anomaly.
One of the key characteristics used to define the K-Pg boundary is the iridium anomaly found in sediments. Iridium is a rare metal that is more abundant in asteroids than in Earth's crust.
The high levels of iridium found in the boundary layer suggest the impact of a large asteroid or comet, which is believed to have contributed to the mass extinction event at the end of the Cretaceous. This iridium layer is a global marker used to define the K-Pg boundary.

Step 3: Analyzing the other options.
- (A) Absence of dinosaur fossils: While the disappearance of dinosaurs is a significant consequence of the K-Pg extinction, it is not used as a precise marker to define the boundary. The extinction of dinosaurs is more of an outcome than a defining feature.
- (C) Presence of high mercury content in sediments: While some studies have noted an increase in mercury related to the asteroid impact, the iridium anomaly is a more widely used and definitive marker.
- (D) End of Deccan volcanism: The end of Deccan volcanism is a contributing factor to the mass extinction but is not the primary global feature used to define the K-Pg boundary. The volcanic activity occurred over a longer period and does not serve as a distinct boundary marker.

Step 4: Conclusion.
The presence of the iridium anomaly in sediments is the most widely used feature to define the K-Pg boundary globally. Hence, the correct answer is (B).
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