A 23-kiloton nuclear bomb detonated on 18 April, 1953, at a Nevada test site released this mushroom cloud. (National Nuclear Security Administration / Nevada Site Office)
Oil plumes threaten to choke the oceans and methane gas explosions shoot sky high -- and those are hardly the biggest threats facing the Earth. From cosmic rays to asteroid impacts to the threat of general destruction, our planet may be less safe than you think.
Here are the top eight risks to life as we know it, detailed by scientists and science fiction writers -- and whether it's even possible to save ourselves.
1. A sudden gamma ray burst strikes
When a supernova explodes, it unleashes a massive gamma ray. Thankfully, most of these tremendous bursts of energy are so far away that they’re harmless. But if one were too close ...
"Were a supernova to explode within 30 light years from the sun -- which is just around the corner in terms of cosmic scale -- it would blow away a portion of the Earth's atmosphere, produce global fires, fry the atmosphere, and kill the majority of species alive on the planet within months, even for species that live underground and hundreds of meters under water," said Annie McQuade, who is working on a book about global calamities.
Gamma rays or other radiation could also cause damage to satellites orbiting the planet. But not to worry, said Chris DePree, a professor at Agnes Scott College and the director of the Bradley Observatory. He noted that the explosion would not only need to be close to Earth, but also pointed in our direction. And there are precious few high-mass stars that could explode, he said, so the probability of the event is quite low.
2. A deadly mind virus kills us all
In his book, Directive 51, sci-fi author John Barnes explained how a "mind virus" could destroy the world.
"In recent years, the Internet has made it possible for ideas to spread very fast and develop very quickly," Barnes said. "There is nothing that says humanity can't collectively come down with a truly bad idea -- something self-destructive, short-sighted, maybe just the equivalent of a mass tantrum."
Sci-fi author Walter Jon Williams detailed the idea in his 2008 novel Implied Spaces. Williams told FoxNews.com that it could be possible in the future to introduce what he called a nano-reconstructor (or some other mind-altering agent) to use a region of your brain for nefarious purposes -- to introduce some other agent that causes you to act violently, for example.
There is no obvious protective measure from a mind virus, but Barrett Caldwell, an aeronautics and astronautics professor at Purdue University, likened it to the known "mass psychogenic illnesses" that have infected people in the past and that were self-contained and isolated.
"The genocide in Rwanda is the closest example I can think of for this kind of behavior," elaborated Howard Davidson, a physicist and Stanford professor. "It required active measures by a large group of instigators, and quite a bit of time to get started." But not to worry, he said. "Even in these cases only part of the population is entrained," he told FoxNews.com.
3. The North and South Poles flip-flop
Every few hundred thousand years, the Earth's magnetic poles reverse. When that happens, they can swirl around for a while before finding their new home. Or they might pick multiple spots on the planet. "The problem is not the poles flipping, but that the Earth's magnetic field draws down solar radiation around its poles," Williams explained. "So if one of the poles parks itself over, say, Chicago, a lot of inhabitants could get burned."
"Magnetic poles do reverse and have done so in the past, but it does not happen suddenly," added Caldwell. "The energy involved makes this unlikely at a rate that would lead to a sudden cataclysm."
Seth Shostak, a senior astronomer at the SETI Institute, told FoxNews.com the real danger is the period during the magnetic reversal when the Earth would be unshielded from atomic particles from space. He said we’d need to protect ourselves using goggles and headgear -- or stay indoors at all times.
4. The universe keeps expanding … and expanding
Williams calls it the Big Rip. We already know that dark energy causes the universe to expand. As it expands faster and faster and stars move farther away from each other, a curious thing happens: The observable universe get smaller -- and atomic particles that can't see each other can't interract.
At that point, "none of the protons or electrons will be in the same universe as another, which means they can't interact via the strong, weak, or electromagnetic force. Which means all matter will fly apart," he said.
Howard Davidson, a noted physicist and Stanford professor, agreed that it could happen. "The atoms get very cold. If you wait long enough some versions of the Standard Model have protons decaying, so they go to neutrons and electrons, and we have some spare electrons left over. Very dull, cold, quiet, end of the universe."
Of course, this process takes eons -- and there is no proof that the expanding universe is in imminent danger. There's also no way to prevent this fateful event from occurring.
5. Extreme science experiments go too far
As past history has shown, the greatest danger to man is often man himself. McQuade explained that modern experiments at the Large Hadron Collider in Switzerland, where scientists are looking for signs of the Big Bang, could lead to strange anomalies. One such potential: creating "strangelets" from reassembling quarks, or elementary particles.
"Strangelets could grow by consuming ordinary nuclei, which would liberate energy, and since there is nothing to stop it, they would ultimately produce a catastrophic explosion," McQuade said. "Smashing particles could also trigger a series of reactions that would result in vacuum instability. Though vacuum instability sounds innocuous enough, it could tear the fabric of space itself."
McQuade said most scientists view these events as extremely unlikely, but as these experiments push the envelope, there is more chance of them going awry. DePree said a more likely doomsday scenario is not that the actual experiment unleashes peril on the world, but that we use the research in a world-ending way. "The most likely way for experiments to go awry is not the experiment itself, but in its later use by humans," he said.
6. Supervolcanoes wipe out the planet
73,000 years ago, a massive supervolcano in South East Asia turned India to cinders. The volcanic winter lasted another two decades and wiped out about 75% of the nascent human race. Of the six supervolcanoes in the world today, Williams said, three happen to be in the United States. One famously lies beneath Yellowstone National Park in Wyoming; the others are in Long Valley, Calif., and Valles Caldera, N.M.
DePree said there is also a chance of "catastrophic volcanism," which can trigger major tectonic plate movement on the planet. Unfortunately, scientists have no counter-measure for supervolcanoes. If they erupt, there's no stopping them. However, DePree offers one small consolation: It’s unlikely that more than one supervolcano would erupt at once.
7. Computers take over everything
One potential cataclysm could already be happening -- one we've created ourselves. As computer technology becomes more advanced, "thinking machines" could eventually emerge that control banks, stock markets, and airports. It sounds like something out of the Terminator movies, but the reality is that "self-aware" machines could become self-replicating.
Initially, this could mean just a bug that infects computer systems controlling transportation and finance, leading to mass pandemonium. Yet a more dangerous threat is from artificial intelligence (AI). McQuade suggests that AI could become more advanced than human intelligence. Once it does, the machines could develop their own programming routines -- or decide that humans aren't necessary. Or take over nuclear armaments and other stockpiles.
"AI is a field that seeks to engineer not just faster-than-human intelligence, but qualitatively better than human intelligence," McQuade said. "Because AI could learn extremely fast (through recursive self-improvement), it would have the capacity, in a short period of time, to make significant leaps in 'intelligence' until it demonstrates qualitatively better-than-human intelligence."
8. A cough goes round the world
One of the most dangerous threats to the world population is a simple cough -- that is, a deadly flu that spreads quickly around the world. Caldwell noted that H1N1 turned out to be very contagious but not very deadly, for which most experts think we were lucky. A more dangerous contagion could spread just as quickly but cause vastly more harm.
Fortunately, Shostak explained, most flu outbreaks tend to be "self-limiting"; usually pathogens kill some of the people all of the time, not all of the people some of the time. That "usually" part is not exactly reassuring, though.
"The flu or some other plague is always a threat, particularly considering how fast the disease could travel in airplanes, trains, and other modern forms of transportation," said Williams. "Another problem is that modern hospitals have become so reliant on antibiotics that they're very careless about sterilization procedures. You'd have to go back to methods practiced in the 1940s for strict sterilization and isolation, and no one remembers how to do that."
The main counter-attack to massive flu outbreaks is simple hygiene. The more we wash our hands, take precautions in public places, and cover our coughs the less likely that a pathogen will replicate quickly. Scientists are also quick to develop vaccines to dangerous flu viruses, so it's unlikely one could spread worldwide.
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