If comets can bring life, they can also take it away. Much evidence supports the theory that a comet or asteroid struck the Caribbean basin 65 million years ago. In this scenario, the first result was an incredible earthquake measuring 12 on the Richter scale. Millions of tons of dust surged upward to form a gigantic cloud. The excavated material rushed out with such force that it quickly circled the Earth. For more than an hour, the surface of the Earth was bombarded with this debris, sending temperatures soaring and setting off a global fire-storm. Larger, slow-moving debris landed close to the main crater, in the Gulf of Mexico, creating miles-high tsunamis that devastated the coasts of Mexico and Florida.
Soon the whole planet was shrouded in a cloud of dust and soot, and for more than a month there was no sunlight anywhere on Earth. The huge amount of nitric oxide in the air created rain dense with sulfuric acid. As the air finally cleared, the temperatures rose again and Earth suffered a severe greenhouse effect lasting tor centuries. It is widely believed that this impact, and the consequent climatic changes, caused the mass extinction that claimed 80 percent of all species, including the dinosaurs. This extinction, in turn, led to the rise of mammals.