The science of predicting whether an asteroid will cause massive casualties is nearly impossible: There have been large meteorites that have hit Earth with very little damage.
"There have been many huge impacts with no extinctions," he says. "It depends on how they hit, where they hit, whether they land in the sea or not."
According to NASA, "there are no threatening asteroids as large as the one that killed the dinosaurs" on the horizon.
Last year, a scientist in the Netherlands genetically altered an H5N1 bird flu virus so that it was transmissible between ferrets, which are often used as stand-ins for humans in lab tests, because they have similar immune systems.
That bird flu strain is particularly dangerous one, known to be very deadly when passed from birds to humans, having killed more than 500 people worldwide since 2004. Luckily, the virus hasn't mutated to be transmissible between humans. The results could be catastrophic otherwise.
When the controversial research was published, Paul Keim, a geneticist with the U.S. National Science Advisory Board for Biosecurity, said the development was particularly scary.
"I can't think of another pathogenic organism that is as scary as this one," he said. "I don't think anthrax is scary at all compared to this."
Over the past year, the sun has been particularly volatile as it reaches what's known as "solar max." Though solar storms have the potential to knock out electronics on Earth, NASA insists that "killer solar flares are a physical impossibility." But one day, if humans or something else doesn't destroy it first, the sun will eventually destroy the Earth.
"It's in all likelihood that if a natural occurrence were to destroy the world, it is 4.5 billion years from now, when our sun starts going through its end-of-life sequence," says Phil Chamberlin, of NASA's solar physics laboratory.
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Jason Koebler is a science and technology reporter for U.S. News & World Report. You can follow him on Twitter or reach him at email@example.com.