End of the World

ARE WE DOOMED?

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The short answer is: Yep. Odds are that a huge asteroid or speeding comet will slam into Earth and destroy all life and perhaps the planet too. Even if that doesn’t happen, our sun will swell into a red giant star about five billion years from now. It will evaporate the oceans and end all life on Earth. Yikes!

But the long answer is more complicated and more hopeful. Most asteroids burn up in the atmosphere without reaching the ground. But there are notable exceptions. On June 30, 1908, a comet or an asteroid exploded in the air over Siberia, Russia. It flattened a forest for miles in all directions, leaving a Paul Bunyan version of a “crop circle.” Plenty of people witnessed the fireball. About 50,000 years ago, an asteroid about a football field in diameter created Meteor Crater in Arizona. The mile wide hole dwarfs tourists who flock to see it. On average, objects as big as this hit earth roughly once in several thousands of years.

Star eating a planet

These two impacts are nothing compared to the last really big impact. To kill off the species, an asteroid needs to be at least half a mile, that is, about a kilometre wide. These medium sized smashers tend to visit Earth about every 300, 000 years or so. They can create monster tsunamis or flatten plenty of miles of real estate.

Really big asteroids, about 6 miles (10 km) in diameter, strike roughly once every 100 million years or so, causing mass extinctions. They kick up so much dust and debris in the atmosphere that little sunlight can get through. Plants die and, soon, some animals that eat the plants die too. The space rock that many scientists think helped kill off the dinosaurs 65 million years ago was probably about 10 miles (16 km) wide.

When will one these killers hit? No one knows. In a minute, or not for millions of years. Meteorites don’t fall on schedule. But they do fall, as the map shows. Even though wind, rain, and volcanoes have worn away traces of most of the Earth’s impact craters, scientists have pinpointed where they’ve landed. Usually, they find rocks that only a high speed impact can create. For example, tektites from when molten rock is tossed into orbit and solidifies into glassy rock on the way down. Also, some asteroids contain an element called iridium that’s rare on Earth.

Asteroid impact

The first challenge to saving Earth from a meteorite is to see it coming. Astronomers are scouring the skies for big and medium asteroids and comets that cross Earth’s orbital path. Really big near-Earth asteroids are rare, but hundreds if medium-sized ones exist. The next step is to avoid or deal with the impact.

End of the world