Scientific Doomsday: Ways the World Could Actually End

2012 is sure to be filled with too many end-of-the-world jokes, and probably a fair amount of genuine fear as well.

But assuming the Mayans were wrong and doomsday isn't on Dec. 21 this year, you may be wondering how the world as we know it might really end. We've collected several scientifically valid scenarios for you to worry about.

Supervolcano

The chances of an earthquake unzipping the world’s fault system are negligible, says seismologist Thorne Lay of the University of California, Santa Cruz.

This is because the energy released by a quake is related to the length of the fault that is ruptured during the event. For example, the 2004 magnitude 9.1 Sumatra quake that triggered the Indian Ocean tsunami and killed nearly 300,000 people, ruptured around 900 miles of a subduction zone fault, the longest ever recorded for a single quake. But the major fault zones that mark boundaries between tectonic plates are not continuous, and irregularities like changes in the type of faulting and the existence of smaller plates with shorter boundaries stop ruptures short of apocalyptic lengths.

But other geologic hazards may have more potential for doom.

“It’s more plausible that you have a truly mammoth eruption,” like an eruption of the supervolcano that lies beneath the Yellowstone National Park area, Lay said. Yellowstone has experienced colossal volcanic explosions in the past, most recently 2 million and 640,000 years ago. Another such mega eruption would be devastating for much of North America, he says.

Giant eruptions have contributed to mass extinctions, including the one that killed off the dinosaurs around 65 million years ago. At that time, volcanoes spewed out a roughly 2,000-foot-deep layer of lava to form part of the 10,000-foot-thick Deccan Traps of India, the world’s largest lava beds, geophysicist Anne-Lise Chenet of the Paris Geophysical Institute wrote in an email. And scientists have also shown that a Siberian volcano may have precipitated the largest extinction on record about 250 million years ago. These blazing behemoths belched out so much sulfur, carbon dioxide and ash that they may have altered the climate enough to collapse the food chain, Lay says.

Yellowstone's giant volcanic crater has risen about 10 inches in the last decade, suggesting molten rock may be building up underneath. During its lifetime, the megavolcano has probably experienced more than a dozen giant eruptions, Lay says. Lately, it’s been blowing off steam through little vents, but it’s unclear whether it’s gearing up for another Earth-shattering blast.

Asteroid Accident

Asteroids typically top the list of extraterrestrial objects that could hit Earth. A 9-mile wide asteroid that crashed into what is now Mexico’s Yucatan Peninsula was partly responsible for the dinosaurs' extinction about 65 million years ago.

The 2004 announcement that 900-foot long Apophis had more than a 2 percent chance of colliding with Earth in 2029 revved up research on asteroid detection and defense, when scientists recalculated the odds down to 1 in 250,000.

Luckily, nothing of that size is in Earth’s path currently, so “we may be safe for at least a few million years,” said planetary scientist Jay Melosh of Purdue University.

But smaller threats may be looming.

NASA expects that roughly every 100 years, an asteroid larger than 55 yards wide will strike. The impact could cause local catastrophes like massive floods, destruction of entire cities and agricultural collapse. Around once every few 100,000 years, chunks of rock more than three-fifths of a mile wide — the equivalent of about 12 New York City blocks — could come tumbling through the atmosphere causing much more serious problems, on a global scale. Acid rain would kill crops, debris would shield Earth from sunlight, and firestorms would ensue, according to NASA’s Near Earth Object Program.

To understand our cosmic risks, scientists are inspecting the solar system to find asteroids that may be heading our way, said UCSC planetary scientist Erik Asphaug. They’ve discovered about 900 of an estimated 1,000 asteroids wider than three-fifths of a mile thought to have an Earth-crossing orbit. None appears to have Earth as its target.

“The plain vanilla odds are very low” that anything already discovered of that size will strike in the near future, Asphaug said. But that doesn’t mean Earth is 100 percent safe.

It’s close to impossible to find every asteroid that could be a threat to Earth.

“There’s always some uncertainty that we’re going to have to live with,” he said. “Or die with.”

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