On February 14, a small asteroid known as the Chelyabinsk object hit southwestern Russia. The next day, a 40-meter-long asteroid called 2012 DA14 passed by the earth, coming closer than our own satellites. These recent encounters with large space rocks bring to mind one of the theories of what killed the dinosaurs millions of years ago: an asteroid strike.

A painting by Donald E. Davis that depicts an asteroid crashing into the Yucatan Peninsula in southeast Mexico.

By studying a 110-mile (180-kilometer) wide crater in the Yucatan Peninsula in Mexico, scientists have determined that the asteroid that struck the earth 66 million years ago was 6 miles in diameter. The collision with Earth would have caused wildfires, tsunamis, and particles in the atmosphere. These particles would have blocked the sun, killing the plant-life and causing temperatures to drop significantly. Many scientists believe this series of events led to the demise of dinosaurs.

Dinosaurs may have been killed by a series of volcanic eruptions in what is now India. Credit: National Science Foundation, Zina Deretsky

But perhaps this wasn’t the only cause of extinction. Many scientists believe that a series of volcanic eruptions that occurred 60-68 millions of years ago in what is now India began killing off the dinosaurs before the asteroid strike. These eruptions would have caused dramatic climate change that would threaten many dinosaur populations.

Learn more about these theories at  National Geographic.