Out-of-control mini self-replicating robots would consume all of the matter on Earth in their endless quest to clone themselves. Not an actual "goo," the tiny nano-robots would move across the planet, replicating infinitely until they run out of raw matter to use. The Earth would be completely overtaken by these machines, and organic life would be no more.

In the MAN-MADE BLACK HOLE scenario…
The CERN Large Hadron Collider in France, the largest and most advanced machine on the planet, would accidentally create a black hole on Earth. A giant particle accelerator used by physicists to study the universe's smallest known particles, it works by crashing beams of them together at high speeds, recreating Big Bang conditions. While the chances of this happening are slim, if the LHC were to accidentally create a black hole and it grew out of control, first the CERN facility, then the countries of France and Switzerland, and eventually the Earth itself would be sucked into its vacant depths.

In the ASTEROID IMPACT scenario…
An asteroid as large as the one that killed the dinosaurs would obliterate the human race. We are, in fact, overdue for another large asteroid collision here on Earth. If it hit, humans, as the dominant life form, would be in danger of immediate extinction—the asteroid would immediately vaporize all living things for miles around and send waves of destruction around the world.

In the GLOBAL CLIMATE CHANGE scenario…
Minor oddities like snow in June and shorts in January would give way to floods overtaking coastal cities, unending droughts, extreme hurricanes, melted glaciers, and acidic oceans. Quickened by pollution and the human race's ever-expanding carbon footprint, Earth's ability to support thriving life would diminish more and more quickly, until finally it would be uninhabitable.

In the EXTREME OVERPOPULATION scenario…
There would be no food. No water. No resources to go around. The Earth's population has more than doubled in the past 50 years. If it continues to grow and becomes too much to control, sanitation would be more and more difficult to accomplish and people would live in squalor. Disease, starvation, and dehydration would claim the lives of the weak and only the strong would survive, attempting to continue the reign of the human race on planet Earth.

In the NUCLEAR DISASTER scenario…
Tensions in the world would continue to grow, and war would become more and more sophisticated. There are over 20,000 nuclear weapons in the world today. If we experienced World War III, we would all be in danger of a global nuclear holocaust. When the bombs did drop, nuclear fallout in the form of deadly radiation and electromagnetic pulses would have immediate and lasting effects on humanity—and if enough of them were deployed, life would no longer be possible in the nuclear wasteland.

In the DEADLY EPIDEMIC scenario…
A natural spread of a new disease—or biological warfare utilizing existing ones—would devastate the world's population, as healthy humans would be decimated by lethal illness. We've seen it before: plague killed as much as one-third of Europe's population in the 14th century, and the Spanish Flu of the late 1910s is believed to have ended more lives than World War I. Even more frightening, it is now technologically possible to equip missiles and bombs with diseases like smallpox, against which much of the world is no longer immune.

In the DEATH OF THE BEES scenario…
The 30 percent of the world's food that relies on bee activity would gradually disappear, causing food shortages and an inevitable struggle for survival. This is not as far-fetched as it may seem. Colony Collapse Disorder (CCD) is an actual syndrome in which all of a colony's worker bees mysteriously die off, leaving a lone queen wandering around the hive. In the winter of 2008, 36 percent of the commercial beehives in the U.S. succumbed to CCD, the direct cause is unknown, and there is no known cure.