Which of the following led the scientists to conclude that a large meteorite had impacted Earth?

The correct answer is (D) The sediments found were enriched with Iridium.

• Logical Principle: The hypothesis concerning the extinction of dinosaurs due to a massive meteorite impact (the Alvarez hypothesis) relies on geochemical evidence found in the Cretaceous-Paleogene (K-Pg) boundary layer.
• Deduction: Scientists discovered that a thin layer of clay deposited worldwide at the K-Pg boundary contains unusually high concentrations of Iridium, an element rare in Earth's crust but abundant in asteroids and meteorites. This provided the definitive chemical signature of an extraterrestrial impact.
• Option Contrast: While the discovery of the Chicxulub crater in the Yucatán (Option A) provided physical site evidence, the initial conclusion of a large impact was scientifically driven by the geochemical anomaly of Iridium (Option D). Options B and C describe non-conclusive findings or secondary observations.