Finding an Abundance of Iridium in the K-Pg Boundary Sequence

question 10

Multiple Choice

Finding an abundance of iridium in the K-Pg boundary sequence worldwide pointed to evidence that this layer was of ____ origin.​

• A) carbon​
• B) ​organic
• C) ​geologically recent
• D) ​prehistoric
• E) ​extraterrestrial

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Definitions:

Rhizobia

Soil bacteria that fix nitrogen after becoming established inside root nodules of legumes.

Infection Threads

Filamentous structures formed by certain bacteria during the infection process of plant roots, facilitating microbial entry.

Legume

(1) A simple, dry fruit that develops from a single carpel and splits open at maturity along two sutures to release seeds. (2) Any member of the pea family (e.g., pea, bean, peanut, alfalfa).

Soil Organisms

A diverse group of living entities in soil, including bacteria, fungi, insects, and earthworms, contributing to nutrient cycling and soil health.