A: it suggests extraterrestrial influence.
Iridium is considered significant in the context of the dinosaur extinction because high levels of iridium are found in the geological layer corresponding to the Cretaceous-Paleogene (K-Pg) boundary. This finding supports the hypothesis that an asteroid impact contributed to the mass extinction event that led to the disappearance of the dinosaurs approximately 66 million years ago. Iridium is relatively rare on Earth's surface but more common in asteroids, suggesting that its presence in this layer indicates an extraterrestrial influence.