There are not nearly enough craters on Earth for the large number of asteroids that impact us every year. Over the past 250 million years, Earth should have been hit around 440 times by asteroids larger than a mile across. But scientists have found only 38 large impact craters from this period. Scientists now think that when many of them hit the Earth, they keep right on going and punch through the Earth’s crust, triggering huge volcanic eruptions.

During the 1948-1952 UFO flap, green fireballs kept appearing over the western U.S. These were officially classified as meteors, and appeared in the same general area of the country as the green fireball that was seen last weekend in the West. Many UFO investigators have speculated about a possible connection between the green fireballs and the high number of UFO sightings that took place during the same time period.

Residents of Utah, Colorado and southern Wyoming saw the fireball Sunday at 7:30 pm, and witnesses say it had a long tail of green, orange and purple flames. “People said it had a 500-foot tail and it was huge, like a meteor, and green and orange,” says Colorado sheriff dispatcher Kristy Lee.

Astronomers want to find all the asteroids that may be heading for an impact with Earth, so they’re searching for the legendary group of asteroids called “Vulcanoids” that may be circling the sun. We can’t see these asteroids, but we know they?re there because they effect Mercury’s orbit and make the planet wobble. In the 19th century, astronomers thought Mercury’s strange orbit must be caused by a hidden planet, which they called “Vulcan,” after the Roman god of fire. Astronomers now think hundreds of space rocks, up to 20 miles in diameter, can be found between Mercury and the sun. They could be pieces of a planet that broke apart millions of years ago, and if the orbit of one of them gets deflected, it could head our way.

An asteroid may have wiped out the dinosaurs 65 million years ago, but an earlier one probably allowed the rise of the giant creatures, who dominated the planet for 135 million years. After their demise, mammals took over and eventually evolved into humans, so our domination was caused by an asteroid as well. Will asteroids also bring about the end of human civilization?