Somewhere deep in space there exists a massive rock, and it has got the Earth in its sights. As we reported recently, the B612 Foundation, a group composed of scientists and astronomers, predicts that the planet is majorly vulnerable to a existence-ending strike, but it is worth looking at the astonishing history of asteroids on our planet to understand the threat that faces us.

Just five years ago, an asteroid of 20 meters in width injured more than 1,000 people and damaged thousands of buildings in Russia. Compare that to the Chicxulub crater, which scientists believe was caused by an asteroid or comet 10 to 15 kilometers in diameter and wiped out the dinosaurs 65 million years ago.

The Cretaceous-Paleogene extinction, as it is known among scientists, is perhaps the best known of the “Big 5.” The fourth was the Triassic-Jurassic extinction 199 to 214 million years ago that may have been a result of an asteroid impact. The third was the worst in Earth history, and it happened 251 million years ago with 96 percent of species lost. That one was likely caused by a huge volcanic eruption.

The second extinction, likely caused by volcanic ash, was the Late Devonian Extinction, which wiped out 75 percent of species about 364 million years ago. And the first major extinction, the Ordovician-Silurian Extinction 439 million years ago, killed 86 percent of life on Earth. This one was most likely caused by glaciation and falling sea levels.

So the question again is not if a mass extinction event will occur in the future, but when. And with an asteroid being the most likely cause, it explains why the B612 Foundation is spending much of their time trying to tackle what may be the defining challenge of our species.

“B612 is an organization that works towards protecting the Earth from asteroid impacts and informing and forwarding world-wide decision-making on planetary defense issues,” the B612 website states. “B612 provides a non-governmental voice on the risks, options, and implications of asteroid data while advancing the technical means by which that data is acquired. We work to make interpretation of asteroid data open and accessible, and we serve as an informed source for an international community of policy makers and scientists who can best help to achieve these goals.”