If Mayan Prophecy Doomsayers Are Right…

On Dec. 21, 2012, the Mayan calendar will reach the end of a 394-year cycle called a b’ak’tun. In no sense does that imply that the world is going to end — the Mayan calendar cycle is no more momentous than our own calendar ticking over from 1999 to 2000. But that doesn’t mean catastrophe won’t strike. There are plenty of risks to life on earth, ranging from disasters that threaten millions or billions of people to an all-out “extinction-level event” that wipes out the majority of life on the planet. To understand the infinitesimally small—but nonetheless real—risk of planetary disaster, it helps to travel back in time. Because such events have happened before. And the results weren’t pretty.

To see the evidence, let’s take a trip. Start with a visit to the American Museum of Natural History in New York City. On the fourth floor, just inside the entrance to the Hall of Saurischian Dinosaurs, you’ll find a chunk of Montana dirt with dark and light bands layered like Neapolitan ice cream. Not very exciting compared to the huge creatures on display nearby. But one thin, grayish-beige layer might explain what exterminated these great beasts: It’s the impact residue of a 6-mile-wide asteroid that struck the Yucatán 65 million years ago. “In its aftermath we see extinctions of everything from single-celled organisms to the largest dinosaurs,” says Mark Norell, chairman of the museum’s paleontology division. Could another one seal our own fate? Or could some other extraterrestrial catastrophe bring us death from above?

Or maybe it could come from below. Twenty-two hundred miles west, in Yellowstone National Park, one of America’s most popular tourist attractions, is another ominous harbinger of destruction. About once every hour, the pool around the Old Faithful geyser explodes in a fountain of spray 145 feet tall. It’s a cool effect, until you consider what powers it: geothermal energy radiating up from a subterranean plug of magma. Every 500,000 years or so, the Yellowstone supervolcano erupts and rains lava and ash for hundreds of miles. An eruption 250 million years ago in Siberia may have released enough carbon into the atmosphere to cause the largest mass extinction in earth’s history, the Permian-Triassic, which wiped out 96 percent of all sea life.

In the cruelest of ironies, the gravest threat to human life on earth may be other life on earth—the microbial kind. Let’s turn our tour of all things apocalyptic to the Netherlands, where virologist Ron Fouchier at the Erasmus Medical Center recently synthesized an airborne version of the H5N1 avian flu. The lethality and frequent mutations of H5N1 make it a serious pandemic threat. The last big influenza pandemic, the Spanish flu of 1918, is estimated to have killed more than five times as many people as World War I. The possibility of a naturally occurring global outbreak is ever present, but the threat from labs is becoming more frightening. “The cost of synthesizing a new organism goes down every year,” says Dr. Ali Khan, head of the Office of Public Health Preparedness and Response at the Centers for Disease Control and Prevention. “A bad guy could make his own smallpox.”

Although imminent destruction seems all around us, the probability of extinction in any one year is vanishingly small. Our long-term prognosis, however, is far darker. Very few species survive through the eons like the alligator and the coelacanth. “The safe bet is that we won’t make it, because 99.9 percent of things don’t,” says Timothy Spahr, director of the Minor Planet Center in Cambridge, Mass., an asteroid- and comet-tracking organization.

We’ve got some time, though. On average, vertebrate species stick around 4 to 6 million years, and modern humans are only about 200,000 years old. And we’re not your typical vertebrates. Our science and technology might ultimately migrate off this little planet altogether. So maybe we’re just getting started.

What are the 12 threats that could end life as we know it? Read the rest of my Pop Mech story here.