'We're paranoid for a reason' collision chronology:
65 million years ago -- A 10-kilometer asteroid strikes north of the Yucatan Peninsula, causes a global firestorm, then a cold snap and finally a global warming that extinguishes the dinosaurs. Mammals move to center stage.
3.3 million years ago -- An impact in Argentina precedes numerous extinctions and a global cooling trend.
50,000 years ago -- An iron meteorite a few dozen meters across gouges the famous 1 mile wide Barringer meteorite crater in Arizona.
1490 -- About 10,000 people die in China when an asteroid breaks up overhead resulting in a mid air explosion.
1908 -- An asteroid estimated at 50 meters across explodes above Tunguska, Siberia, blowing down trees across 2,000 square miles and killing a thousand reindeer, but apparently no people. Because the stony object exploded in the atmosphere, there's no crater.
1937 -- Asteroid Hermes -- about a mile in diameter -- misses Earth by 600,000 miles. Hermes, although smaller than the asteroid that supposedly wiped out the dinosaurs, could have been a true "category killer," able to cause epic devastation and kill millions.
1980 -- Spacewatch program starts at the University of Arizona, intent on cataloging asteroids. The goal is to get a statistical picture of orbiting rocks anywhere in the solar system.
1994 -- Comet Shoemaker-Levy 9 breaks apart, then smashes into Jupiter under the watchful eye of dozens of telescopes. The resulting zone of chaos is estimated to be as large as the Earth and lends urgency to the search for asteroids and comets. Shoemaker-Levy was a turning point, if it can happen in front of your nose -- practically in your backyard -- it can also happen on Earth.
1998 -- Greenish glass bodies found in Argentina associated with the extinction of 36 local animals (including one we'd love to see, a carnivorous, flightless bird). The glass contains iridium, the same chemical that helped prove the impact theory of dinosaur extinction. Still, correlation is not proof. The climate change -- the sudden, dramatic cooling came immediately after the impact, still we were careful to call this a coincidence.
2000 -- NASA's Near-Earth Asteroid Tracking System announces new data about large asteroids. "Until now, scientists thought the population of large, near-Earth asteroids was between 1,000 and 2,000, but we've downgraded that number significantly.We now believe there are between 500 and 1,000 near-Earth asteroids larger than one kilometer in diameter.
2000 --An Australian engineer, announces a new computer analysis of asteroid impacts indicating that asteroids may cause considerable chaos over a 100,000-year period. Most disturbing was a 5-kilometer asteroid, which exploded with a power of 23 million megatons, easily enough to wipe out the human population. It is estimated the annual risk of a fatal asteroid impact at one in 90, and concluded that an average of 120,000 people died per event. A particular concern was tsunamis. When an asteroid hits the ocean, which covers about 70 percent of the planet, it can trigger a tsunami. According to the simulation, the average tsunami would kill 470,000 people.
The Apophis pass in 2029