Select all of the answers that apply. the cretaceous-tertiary extinction, the most famous of the big five, has been attributed to what major event(s) that triggered the extinction of the dinosaurs? an asteroid hitting the earth massive volcanoes erupting around the world rapid growth of forests on land surfaces falling sea levels increased competition from mammals

The major event that is generally contributed to the Cretaceious-Tertiary extinction is the impact of an enormous asteroid, known as the Chicxulub asteroid. The asteroid struck near the Gulf of Mexico, and evidenced supports that it had a destructive effect on the entire globe. 

While the asteroid is generally accepted as the main event, scientists argue the relevance of changing sea levels and massive volcano eruptions as contributing causes as well. 

Large-scale deforestation (likely due to low sunlight caused by the ash from the asteroid impact and volcano eruptions ) occurred and contributed to the mass extinction, but rapid growth of forests on land was not a factor. In fact, the opposite occurred. 

Mammals benefited from the extinction of larger reptilian predators, and in the millions of years that followed, became the dominant class of animal. However, when they coexisted, they occupied a very different niche from the dinosaurs, and in any case mammals were not abundant enough to compete with the dominant species of the time.