We're All Gonna Die! (continued)
"The top speed of a swimmer or flyer is proportional to its length," Dyson notes. "A generous upper limit to the speed of a nanorobot flying through air or swimming through water would be a tenth of an inch per second, barely fast enough to chase a snail."
Voracious Black Holes!
If such a rogue black hole happened to find its way into the solar system, its gravitational influence would disrupt the orbits of all the planets and their moons. Earth might slingshot out of the temperate range it now occupies and into frigid reaches more familiar to Mars, or it might be pushed closer to the sun to be singed, charred, or vaporized. Worse, if a sufficiently large black hole were to pass through the globe, it might be lights-out in more ways than one. The planet would be sucked into a vortex of such intense gravity that nothing would escape. The atoms that once made up Earth would be crushed out of existence as it's currently understood.
An encounter between Earth and a black hole is astronomically, as it were, improbable. However, collisions with supermassive objects of any kind would not be survivable.
7. Shifting magnetic poles! As Earth turns, spinning molten rock in its core generates a magnetic field that surrounds the planet. The magma hasn't stopped turning, as happens in the movie The Core. But magnetic effects preserved in Oregon lava flows show that the world's magnetic polarity swaps from time to time. Exactly what causes these reversals is unknown. The last one seems to have happened 16 million years ago, but some researchers speculate that Earth's polarity may change as often as every 10,000 years.
In the aftermath of such an event, a compass needle would point toward Antarctica - but it's the event itself that worries some scientists. As the magnetic poles lurch, charged bodies of lava would suddenly become repelled by areas that once attracted them, causing earthquakes and other seismic disturbances. All magnetic fields might collapse briefly, playing havoc with electronics. Earth's magnetic field repels some forms of solar and cosmic rays; if the field faltered, radiation would pound the planet's surface, possibly killing plants, animals, and people in significant numbers.
It's hard to know how scary polar shift really is, since the frequency of such events is unknown. Anyway, what can anyone do about it? Nada.
Much of India sits on a basalt formation geologists call the Deccan Traps. Hundreds or thousands of huge volcanoes are believed to have erupted in this region, the cataclysms lasting many millennia and covering much of the subcontinent with molten basalt to a depth of 1,000 feet. The Deccan Traps burst forth about 65 million years ago, coincident with the dinosaurian demise. Some researchers think the meteorite usually blamed for that event struck with such violence that it cracked tectonic plates, setting in motion unimaginable seismic upheaval. In addition to 100 percent destruction within the path of the 1,000-foot tidal wave of lava, the Deccan Traps eruptions would have caused an ice age, choking global megasmog, and acid rain from hell.
The Deccan Traps were a municipal fireworks display compared with a huge Siberian basalt formation called the Siberian Traps, the product of eruptions lasting 600,000 years. Those occurred about 250 million years ago, coincident with the Permian extinction - the worst mass extinction in the fossil record.
Then there are supervolcanoes, individual eruptors of extraordinary size and power, far more potent than Krakatau. Some are geologically recent. A supervolcano called Toba exploded near Sumatra 73,000 years ago. Toba pumped 5 billion tons of sulfuric acid into the atmosphere and spewed so much sun-blocking ash that global temperatures are believed to have fallen 9 degrees Fahrenheit for several years - the difference between current temperatures and those of the Pleistocene ice age. Remember the "out of Africa" theory that we're all descended from a small group of people who lived in Olduvai Gorge? They may have been the sole members of genus Homo to survive the supervolcano's global aftereffects.
Nobody knows what triggered the Toba eruption or how to estimate when the next supervolcano will detonate. Disturbing thought: According to the US Geologic Survey, a supervolcano in Yellowstone National Park may be ripe for explosion.
9. Sudden climate change! The world has become 1 degree warmer in the past century. So far, that rise hasn't hurt anyone - in fact, it may have contributed to the ever-higher crop yields that have staved off predicted Malthusian famines - but it's reasonable to expect that global temperatures will get warmer, owing at least in part to artificial greenhouse gases. Eventually the extra warmth might cease to be benign.
The notion that greenhouse gases could trigger such a rapid change keeps serious scientists up at night. Ocean currents, whose dynamics are poorly understood, appear to have been central to past climate shifts. What if they suddenly started changing? Western Europe - most of which lies to the north of Maine - is nicely habitable owing to the Gulf Stream, a conveyor belt of warm water that churns past England. If global warming somehow altered the Gulf Stream's course, the European Union might be plunged into a deep freeze even as world temperatures rise.