Heredity, Natural Selection, and Evolution


What is one of the most famous mass extinctions and why?

One of the most famous mass extinctions occurred around sixty-five million years ago, between the Cretaceous and Tertiary periods: the demise of about 76 percent of species—including the dinosaurs. Speculations over time as to the reason included a change in the climate due to volcanic eruptions or a difference in output from the Sun, making it difficult for the dinosaurs to adapt and survive.

The most “agreed-upon” solution for the dinosaur demise is the impact theory: objects from space collided with the Earth and changed the climate. Scientists know of impact craters on the Earth—evidence that comets and asteroids have struck our planet in the past. The one impact crater they are pointing to the most is found around the Yucatan peninsula in Mexico—the Chicxulub—an impact crater that dates to around the demise of the dinosaurs. Although it may only be partially responsible, scientists speculate that the impact would throw enough dust and debris high into the atmosphere to filter or block out the sunlight; the result would be a change in the worldwide climate. Vegetation would change, as would the normal habitats of the creatures. Eventually the food chain would collapse—as would the dinosaur species.


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