After ruling the Earth for more than 160 million years, the dinosaurs finally met their doom thanks to a visitor from outer space. About 66 million years ago, an asteroid at least 6 miles (10 kilometers) in diameter dealt the world of dinosaurs a devastating blow, causing earthquakes, tsunamis, volcanic eruptions, and climate catastrophes that soon wiped out 75 percent of all living creatures.
But through it all, Earth she remained.
Does this mean our planet is immune to an asteroid Armageddon? If the dreaded stargazer-killing asteroid wasn’t enough to end the world, then what would it take? Could a space rock really destroy the entire Earth – and how big would it have to be?
Related: 8 Ways to Stop an Asteroid: Nukes, Paint and Bruce Willis
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 did moonwithout destroying the Earth,” Brian Thune, a professor of atmospheric and oceanic sciences at the University of Colorado Boulder who has studied asteroid impacts, told Live Science in an email.
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, launching a salvo of rocky debris into space that eventually coalesced into our moon. (Mars is about 4,200 miles, or 6,700 km wide — more than 500 times the width of the dinosaur-killing asteroid.)
Instead of obliterating our planet, scientists think that part of Theia’s core and mantle merged with ours, remaining underfoot for centuries to come when the first life evolved. Experts disagree as to whether this ancient collision was head-on or just a glancing blow, but there’s no doubt that if there was 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.)
Death from above
As the mass extinction of the birdless dinosaurs shows, it takes much less than a rogue planet to seriously destroy life on Earth, even if the planet itself remains. NASA considers any space rock a potential hazard if it is at least 460 feet (140 meters) in diameter and orbits within 4.6 million miles (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, at least 0.6 miles (1 km) wide, would “likely trigger the end of civilization” by unleashing global climate catastrophes, said Gerrit L. Verschuur, an astrophysicist at Rhodes College in Memphis, Tennessee. , said Scientific American (opens in new tab). And if a dino-killing asteroid-sized impactor were to arrive today, it would likely wipe out humans (and countless other species).
“In general, the initial impact creates a huge fireball that kills anyone who can see it,” Verschuur said. “Then dust from the impact and smoke from the fires envelop the Earth, plunging our planet into a so-called impact winter.”
During this period of suffering, so much dust and noxious gases would cloud the sky that plants could no longer convert sunlight into energy through photosynthesis (opens in new tab). Plant life would disappear around the world and animals would soon follow suit. Only very small land-dwelling animals (like our early mammalian ancestors) could survive.
Understandably, NASA and other space agencies take the threat of asteroid impacts very seriously, closely monitoring thousands of potential impactors in our solar system. The good news is that there is no danger of a potentially dangerous asteroid reaching our planet for at least the next 100 years.
And, if a potentially dangerous space rock unexpectedly changes course and puts our planet in its sights, NASA is testing a plan to deal with it. On September 26, the space agency smashed an unmanned rocket (opens in new tab) to a 525-foot-wide (160 m) asteroid called Dimorphos, in hopes of slightly altering the space rock’s orbit.
Fortunately, Dimorphos is not headed for 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 against future asteroid impact fears.
Dinosaurs would be jealous.
Originally published in Live Science.