Final answer:
Elevated levels of iridium at the K-Pg boundary are unusual and indicate a rare event, which is supported by the asteroid impact hypothesis. This hypothesis is corroborated by the discovery of an impact crater in the Yucatan Peninsula and changes in biodiversity such as an increase in fern spores after the event.
Step-by-step explanation:
The elevated levels of iridium found in the geologic layer at the K-Pg boundary are indeed unusual. Iridium is typically scarce in the Earth's crust, but it is abundant in most meteorites. The discovery in 1980 by scientists Luis and Walter Alvarez, Frank Asaro, and Helen Michels of a worldwide iridium anomaly was groundbreaking. They hypothesized that this anomaly was due to an asteroid impact that marked the end of the Cretaceous period and led to a mass extinction event. This event is notably associated with the disappearance of the dinosaurs among other species.
The layer of iridium serves as a critical piece of evidence for the asteroid impact hypothesis. The high concentration of iridium in the Cretaceous-Paleogene layers, along with other factors such as the discovery of a large impact crater in the Yucatan Peninsula, have led to widespread acceptance of this theory among scientists. The iridium spike is also associated with significant changes in biodiversity, including an increase in fern spores above the K-Pg boundary, which indicates a dramatic change in plant life after the impact event.