What would be the most convincing evidence that an extraterrestrial event had led to a climatic change that resulted in extinction of a group of organisms?

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High iridium concentrations are often found in a thin layer of sedimentary rock between strata of the Cretaceous and Paleogene periods, which suggests that an extraterrestrial event (such as an asteroid impact) led to the extinction of the dinosaurs and other organisms. This is considered a strong piece of evidence for an extraterrestrial cause for a climatic change that resulted in extinction of a group of organisms.

What Would Be the Most Convincing Evidence That an Extraterrestrial