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: What the K-Pg boundary marks.
The K-Pg boundary closes the Cretaceous and opens the Paleogene, tied to a great mass extinction. We want the feature used to mark it worldwide.

Step 2: The asteroid signature.
The boundary clay holds a strong spike of iridium. Iridium is rare in crustal rock but common in asteroids, so the spike points to a large impact.

Step 3: Why iridium is the marker.
This iridium layer turns up at the same level all over the world, which makes it a clean global marker for the boundary.

Step 4: Reject the others.
The loss of dinosaurs is a result, not a precise marker. High mercury and the end of Deccan volcanism are linked events but are not the defining global signal.

Step 5: Final choice.
So the defining feature is the iridium anomaly in the sediments.
\[ \boxed{\text{Presence of iridium anomaly in sediments}} \]