Our planet is tougher than you think - but people aren't.

After dominating the Earth for more than 160 million years, the dinosaurs finally met their doom thanks to a visitor from space.

About 66 million years ago, a 10-kilometer asteroid dealt a devastating blow to the world of dinosaurs, triggering earthquakes, tsunamis, volcanic eruptions, and climate catastrophes that quickly wiped out 75% of all living creatures.

But through it all, Earth itself remained.

Does this mean our planet is immune to an asteroid Armageddon? If the dreaded dinosaur-killing asteroid wasn't enough to end the world, then what would be?

Could a space rock destroy the entire Earth – and how big would it have to be?

The short answer is: It would probably take a rock the size of a planet to destroy our planet. But it would take much, much less to wipe out life on Earth—or most of it, anyway.

"An object larger than Mars hit Earth early in its history and created the Moon, without destroying Earth," Brian Toon, a professor of atmospheric and oceanic sciences at the University of Colorado Boulder, who has studied asteroid impacts.

Toon refers to the giant impact hypothesis - a scientific theory that suggests a Mars-sized planet called Theia collided with Earth 4.5 billion years ago, sending a shower of rocky debris into space that eventually coalesced into the moon. ours.

Scientists theorize that part of Theia's core and mantle melted with ours, remaining underfoot in future eons when the first life evolved.

Experts disagree on whether this ancient collision was head-on or just a glancing blow, but there's no doubt that if there had been anything alive on Earth at the time, Theia would have wiped it out. Scientists think life could have appeared as early as 4.4 billion years ago, a few million years after Theia's impact.

As the mass extinction of the dinosaurs shows, it takes much less than a rogue planet to destroy life on Earth, even if the planet itself remains.

NASA considers any space rock a potential hazard if it is at least 140 meters in diameter and orbits within 7.4 million km of Earth. An impact from such a rock could wipe out an entire city and destroy the land around it, according to NASA.

A collision with a larger rock, measuring at least 1 km across, would probably cause the end of civilization by triggering global climate catastrophes, says Gerrit L. Verschuur, an astrophysicist at Rhodes College in Memphis, Tennessee.

And if an impactor the size of the dinosaur-killing asteroid were to arrive today, it would surely make humans and countless other species extinct.

"Generally, the initial impact creates a huge fireball that kills anyone who can see it. Then dust from the impact and smoke from the fires surround the Earth, plunging our planet into the so-called impact winter," Verschuur said.

During this season of suffering, so much dust and noxious gas would cloud the sky that plants could no longer turn sunlight into energy through photosynthesis.

Plant life would disappear worldwide and animals would soon follow suit. Only very small, land-dwelling animals, like our early mammalian ancestors, would have had a chance to survive.

NASA and other space agencies take the threat of asteroid impacts very seriously, closely monitoring thousands of potential impacts in our solar system.

The good news is that there is no threat of any potentially dangerous asteroids reaching our planet for at least the next 100 years.

And, if a potentially dangerous space rock should suddenly change course and put our planet in its sights, NASA is testing a plan to deal with it.

On September 26, the space agency successfully shot an unmanned rocket at a 160-meter-wide asteroid called Dimorphos, altering its trajectory.

Dimorphos wasn't coming toward Earth, but through this mission — known as the Double Asteroid Redirect Test (DART) — NASA hopes to test whether crashing a spacecraft into an asteroid is a viable means of planetary defense in the future. .