About 65.5 million years ago, nearly all large vertebrates and many tropical invertebrates became extinct in what was clearly a geological, climatic and biological event with worldwide consequences. In 1979, a geologist who was studying rock layers between the Cretaceous and Paleogene periods spotted a thin layer of grey clay separating the two eras. Other scientists found this grey layer, now called the K-T boundary, all over the world, and tests showed that it contained high concentrations of iridium, an element that is rare on Earth, but common in most meteorites. Also within this layer are indications of “shocked quartz” and tiny glass-like globes called tektites that form when rock is suddenly vaporized then immediately cooled. Considering this data, what is the most plausible explanation for this extinction event?

Question

About 65.5 million years ago, nearly all large vertebrates and many tropical invertebrates became extinct in what was clearly a geological, climatic and biological event with worldwide consequences. In 1979, a geologist who was studying rock layers between the Cretaceous and Paleogene periods spotted a thin layer of grey clay separating the two eras. Other scientists found this grey layer, now called the K-T boundary, all over the world, and tests showed that it contained high concentrations of iridium, an element that is rare on Earth, but common in most meteorites. Also within this layer are indications of “shocked quartz” and tiny glass-like globes called tektites that form when rock is suddenly vaporized then immediately cooled. Considering this data, what is the most plausible explanation for this extinction event?
Responses
A	The K-T extinction event most likely resulted from the most recent ice age.The K-T extinction event most likely resulted from the most recent ice age.
B	The K-T extinction event most likely resulted from a massive volcanic eruption.The K-T extinction event most likely resulted from a massive volcanic eruption.
C	The K-T extinction event most likely resulted from an asteroid impact that caused widespread geographic and climactic changes.The K-T extinction event most likely resulted from an asteroid impact that caused widespread geographic and climactic changes.
D	The K-T extinction event most likely resulted from a long drought even that slowly caused the loss of large vertebrates and proliferation of smaller species.The K-T extinction event most likely resulted from a long drought even that slowly caused the loss of large vertebrates and proliferation of smaller species.

GPT-4o mini · Answer

The most plausible explanation for the K-T extinction event, based on the evidence of high iridium concentrations, shocked quartz, and tektites found in the K-T boundary layer, is:

C: The K-T extinction event most likely resulted from an asteroid impact that caused widespread geographic and climactic changes.

This interpretation is supported by the presence of iridium, typically associated with extraterrestrial materials, and the geological evidence of widespread disruptions that would have followed such an impact, leading to the mass extinction observed in the fossil record.