An artist's depiction of a large impact event, in this case striking the ocean. Chances are that meteors and comets will strike the Earth's oceans, since 71% of the surface of the Earth is ocean.
It's not true that all dinosaurs went extinct
Between 66 and 65 million years ago, the reign of all dinosaurs, with the exception of birds, came to an end in a short amount of time. The top reason for this is thought to be a large object whizzing through space, most likely a comet, which struck the Earth with devastating worldwide consequences.
It’s odd that this extinction event is most famous for killing off the dinosaurs, when in fact one group survived, the avian dinosaurs, which are the ancestors of modern birds. There were other animal groups that really were entirely wiped out. Some of those that disappeared forever include ammonites, mosasaurs, and plesiosaurs in the oceans, and pterosaurs in the air.
Map of Cretaceous Earth showing the impact site:
The impact occurred at a site that is now situated partially upon Mexico's Yucatan Peninsula, and partially in the Gulf of Mexico.
Massive object, massive impact
The object was about six miles (ten km) in diameter, and struck Earth at tens of thousands of miles per hour at what is now the Yucatan Peninsula in Mexico, as shown above. The resulting explosion was so violent, and released so much energy, that if it was measured according to the Richter scale for earthquakes, it would measure as a magnitude 12.5 earthquake.
The strongest earthquake ever recorded was magnitude 9.6 in Chile, South America in 1960. According to how the Richter scale works, the calculations mean that the comet impact released about 22,000 times as much energy!
Tyrannosaurs went extinct
This is the famous fossil skeleton Sue, now located at the Field Museum of Natural History in Chicago, Illinois. Tyrannosaurus rex was one of many dinosaur species that became extinct at the end of the Mesozoic Era. This particular skelton is 40 feet (12 meters) long, and the animal probably weighed somewhere close to 15,000 lbs (6,800 kg).
Devastating consequences for life on Earth
The planet’s climate was instantly altered and did not recover for hundreds of thousands of years. In total, the majority of species on the Earth went extinct. Some groups were entirely wiped out, the most major of which were mentioned above.
Over billions of years, Earth has been struck by objects flying through space many times. The Earth's oceans, weather, erosion, volcanic activity, and plate tectonic processes hide a lot of the evidence, which is why we see few craters on the Earth’s land masses compared with the surface of the moon.
Out of all impacts known through geological evidence, only two were larger than the one that ended the era of the dinosaurs. They occurred 1.8 billion and 2.0 billion years ago. In other words, this was the largest such impact in the last 1.8 billion years.
The great extinction event that divides the Mesozoic Era from the modern Cenozoic Era allowed mammals to flourish, and for primates to evolve, and then for human beings to become the dominant species upon planet Earth.