Final answer:
The hypothesis that an asteroid impact killed the dinosaurs came from a spike in iridium levels in geological strata, marking the end of the Cretaceous period. The discovery of a crater near the Yucatán Peninsula and subsequent geological evidence has supported this theory. The asteroid impact is attributed as the critical event leading to the mass extinction known as the 'great dying'.
Step-by-step explanation:
The discovery that an impact killed the dinos is rooted in geological and astrophysical evidence. In 1980, scientists proposed that a spike in iridium levels found in geological strata marking the Cretaceous-Paleogene boundary was due to a large asteroid impact, as iridium is rare on Earth but common in meteorites. This layer corresponded with the sudden disappearance of dinosaurs from the fossil record.
The best-documented evidence of this catastrophic event occurred 65 million years ago, near the Yucatán Peninsula. This marked the Cretaceous period's end and led to a mass extinction event, also known as the "great dying." While mass extinctions can occur due to various reasons, the asteroid was likely the critical factor that led to the extinction of the dinosaurs. It might have been the 'final straw' in a series of climatic disturbances.
In 1991, the discovery of a crater of the correct size and age supported the asteroid impact hypothesis. Now, there is an abundance of geological evidence backing this theory. The immediate aftermath of the impact, which included a debris cloud blocking sunlight, would have been devastating for plant and animal life leading to a prolonged impact on biodiversity.