Threat one: Solar storms
We can look at the major extinction events on Earth as evidenced by the fossil record. We can do this going back more than million years in time, thanks to the evidence found in sedimentary rock, allowing us to see what percent both existed and also died off in any given interval. We can then look for patterns in these extinction events. The easiest way to do it, quantitatively, is to take the Fourier transform of these cycles and see where if anywhere patterns emerge.
There is some relatively weak evidence for a periodicity, under this method, with a frequency of million years, and another, slightly stronger piece of evidence for increased events at 62 million years. If you include these smaller, marine-based-only extinction events, though, what happens to the analysis? Or do they really, truly occur at intervals that are indistinguishable from random?
In , the strongest evidence yet was put forth by scientists Fabo Feng and Coryn Bailer-Jones, who took the full suite of available data and looked at what the likelihood was of having a periodic effect, versus a uniform random effect. At first glance, you might see three candidate effects: The 62 million year periodicity is the largest effect we can see, but even at that, with a likelihood ratio of It suggests that we might be more likely to have a mass extinction at approximately 62 million years before-or-after another mass extinction event, but even that evidence is pretty weak.
The timescale most often cited for periodic mass extinctions, this 26—30 million year periodicity, has absolutely no evidence for it.
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Moreover, Feng and Bailer-Jones explicitly state the following emphasis mine:. Asteroid and comet strikes may have increased likelihoods at certain times, and there may be a periodic effect for CO2 levels and the carbon crustal cycle, but neither one has any evidence linking them to mass extinctions. When it comes to catastrophic events for the planet, and the species that inhabit it, randomness is as good as it gets.
Ethan has authored two books, Beyond The Galaxy , and Treknology: Of the nearly 15, NEOs discovered so far, none are currently on a collision course with Earth. Eventually, however, an Earth-bound NEO of some size will confront humanity with a disaster movie scenario. Science is already on the case.
In Defending Planet Earth: National Research Council, researchers highlighted several potential options for fending off an interloper, given a few decades of warning. We could whack it off course by ramming it with a spaceship or two, slowly alter its orbit with the sustained gravitational pull of a spacecraft called a gravity tractor, or blast it with nuclear explosions. Right now, these planetary defense strategies exist mainly on paper, but some may see real-world tests in the next decade.
NASA has also announced plans to use an enhanced gravity tractor—in which the spaceship collects material from the asteroid to increase its mass—on its Asteroid Redirect Mission, which was set to launch in but now faces funding setbacks. In the event of an actual threat, many researchers favor a combination of these techniques, just to be safe.
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But for objects larger than 1 kilometer across—and for comets, which could appear with little notice—some scientists think the nuclear option is the only option. The idea would be to jolt the body, not blow it up, which could do more harm than good. Although the United Nations Outer Space Treaty currently bars sending nuclear weapons into space, scientists already have a good understanding of the technology, and last year, NASA and the Department of Energy announced a joint effort to hone its use against asteroids.
Ash spreads across North America in computer-simulated eruption of the Yellowstone supervolcano. Geologists read the histories of such blasts in deposits of erupted material called tuff, and the rock record shows that super-volcanoes tend to be repeat offenders.
None of these danger zones now poses a threat.
Global catastrophic risk
But in the event of another eruption, everything within a hundred kilo- meters or so would be incinerated, and ash would blanket continents. Just a few millimeters of the stuff can kill crops; a meter or more can make land unusable for decades, says Susanna Jenkins, a volcanologist at the University of Bristol in the United Kingdom.
Ash can also crush buildings, foul water supplies, clog electronics, ground airplanes, and irritate lungs. These regional impacts could ripple around the world in unexpected ways. Most far-reaching of all, however, would be the effects on global climate, which would resemble those of a large asteroid impact. Just how bad things would be is hard to say. Knowledge of smaller eruptions can help, but it may be an unreliable guide.
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For instance, although supereruptions probably produce loads of sulfate aerosols, the aerosols may be larger and rain out faster than those from smaller eruptions , according to research by Claudia Timmreck, a climate modeler at the Max Planck Institute for Meteorology in Hamburg, Germany, and others. The biggest uncertainties surround potential warning signs.
Researchers think that widespread clues such as earthquakes, increased outgassing, and ground deformation due to rising magma would precede a major eruption. This unrest would begin months, if not many years, in advance, theoretically affording ample time to evacuate residents and set emergency response plans in motion.
However, scientists would struggle to decide when to sound the alarm, says Jacob Lowenstern of the U. Then there are the political challenges of responding to the threat. False alarms can cause trouble, too. The challenge for scientists is to tell which indicators portend a catastrophic eruption instead of a small one—or none at all.
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For now, researchers say, their best bet is to continue studying the plumbing that feeds volcanoes and to squeeze as much information as possible from smaller future eruptions before the next supervolcano lets loose. In the end, no amount of research can do much to prevent or mitigate supervolcanoes, or other freak events such as nearby supernova explosions and cosmic blasts of gamma rays. Our only hope of surviving them is a fallback plan.
And the bottom line in that plan is food. At least two scientists have already sketched out a blueprint. Denkenberger, an architectural engineer at Tennessee State University in Nashville, started moonlighting as a catastrophe researcher a few years ago after reading that fungi may have thrived after previous mass extinctions. Indeed, people could grow mushrooms on leaf litter and on the trunks of trees killed by the disaster, Denkenberger says. Even better would be raising methane-digesting bacteria on diets of natural gas, or converting the cellulose in plant biomass to sugar, a process already used to make biofuel.
Of course, a few other ingredients would have to survive as well: Whether human society endures or snaps is the unknown on which everything else could hinge, says Seth Baum, executive director of the Global Catastrophic Risk Institute in New York City, a nonprofit think tank whose researchers include Denkenberger.
To him, social resilience after a catastrophe is just another question for scientists to address, instead of leaving it to dystopian writers and doomsday preppers. Not that he has anything against survivalists. By Martin Enserink Sep. By Jeffrey Mervis Sep. By Jocelyn Kaiser Sep. In , satellites tracked this coronal mass ejection from the sun as it barely missed Earth. The most inexorable threat to our modern civilization, however, is homegrown—and it strikes much more often than big cosmic impacts do.
Every , years or so, somewhere on Earth, a caldera up to 50 kilometers in diameter collapses and violently expels heaps of accumulated magma. The resulting supervolcano is both unstoppable and ferociously destructive. One such monster, the massive eruption of Mount Toba in Indonesia 74, years ago, may have wiped out most humans on Earth, causing a genetic bottleneck still apparent in our DNA—although the idea is controversial.