The Chicxulub asteroid, responsible for the extinction of the non-avian dinosaurs, is estimated to have been about 10 to 15 kilometers (6 to 9 miles) in diameter. To put that into perspective, it was roughly the size of Mount Everest turned upside down, or large enough to span the entire length of Manhattan Island.
When this massive object struck Earth approximately 66 million years ago, it hit with the force of billions of atomic bombs, creating the Chicxulub crater in what is now the Yucatán Peninsula in Mexico. The crater itself is about 180 kilometers (110 miles) in diameter and 20 kilometers (12 miles) deep, though much of it is now buried under sediment.
The impact triggered a cascade of catastrophic events, including massive tsunamis, widespread wildfires, and a global winter caused by dust and aerosols blocking out the sun. This rapid and severe environmental change led to the K-Pg (Cretaceous–Paleogene) extinction event, wiping out about 75% of all plant and animal species on Earth.
Pro tip: While the asteroid's size is impressive, it was the angle and speed of impact, combined with the specific geology of the impact site (rich in sulfur-bearing rocks), that made it so uniquely devastating. The sulfur released into the atmosphere amplified the global cooling effect, making the aftermath far more lethal than a similar-sized impact elsewhere might have been.