Read more: 鈥�100,000 AD: Living in the deep future鈥�
WHAT are the odds we will avoid extinction? In 2008, researchers attending the in Oxford, UK, took part in an of what they thought were the risks to humanity. They gave humans only a 19 per cent chance of surviving until 2100. Yet when you look more closely, such extreme pessimism is unfounded. Not only will we survive to 2100, it鈥檚 overwhelmingly likely that we鈥檒l survive for at least the next 100,000 years.
Take calculations by J. Richard Gott, an astrophysicist at Princeton University. Based on 200,000 years of human existence, he estimates we will likely last anywhere from another 5100 to 7.8 million years (快猫短视频, 5 September 2007, p 51).
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Fossil evidence is similarly reassuring. Records in the rocks suggest that the average species survival time for mammals is about a million years, though some species survive . It seems there is plenty of time left on our clock. Plus, if you鈥檒l excuse the blowing of our own trumpet, we are the cleverest of the mammals.
Mind you, this could be seen as a problem. Probably the greatest threat to an advanced civilisation is technology that runs out of control; nuclear weapons, bioengineering and nanotechnology have all been cited as bogeymen. But disaster expert Jared Diamond, a geographer at the University of California, Los Angeles, points out that we no longer live in isolated civilisations. Humanity is now a global network of civilisations, with unprecedented access to a diverse, hard-won pool of knowledge already being harnessed for everyone鈥檚 protection.
We are also unlikely to be extinguished by a killer virus pandemic. The worst pandemics occur when a new strain of flu virus spreads across the globe. In this scenario people have no immunity, leaving large populations exposed. Four such events have occurred in the last 100 years 鈥� the worst, the 1918 flu pandemic, killed less than 6 per cent of the world鈥檚 population. More will come, but disease-led extinctions of an entire species only occur when the population is confined to a small area, such as an island. A severe outbreak will kill many millions but there is no compelling reason to think any future virus mutations will trigger our total demise.
More scary is the prospect of a supervolcano eruption. Every 50,000 years or so, a supervolcano somewhere erupts and ejects more than 1000 cubic kilometres of ash. Such events have been linked with crashes in human population. Around 74,000 years ago, Toba erupted in Sumatra.
Anthropologists have suggested that the event may have reduced the human population of Earth to just a few thousand (快猫短视频, 17 April 2010, p 28). But as Bill McGuire, director of the Benfield Hazard Research Centre at University College London, points out, there were many fewer humans then and they were largely confined to the tropics, a geographical concentration that made the eruption鈥檚 impact much more severe than would be the case with today鈥檚 widely distributed population. 鈥淲iping out 7 billion people today would be far more difficult,鈥� he says.
Judging by their historical frequency, it is estimated that the chance of a super-eruption in the next 100,000 years is between 10 and 20 per cent. With colossal clouds of ash plunging the surface of Earth into darkness for five or six years, global harvests would be badly hit for long enough to cause loss of life on an unprecedented scale. 鈥淭he likely death toll would be in the billions,鈥� McGuire says. But it would have to happen twice in that timescale for a realistic chance of human extinction. That鈥檚 not impossible, just statistically extremely unlikely.
Deep impact
The biggest extinction threats of all come from space. Solar flares, asteroid strikes and bursts of gamma rays from supernova explosions or collapsing stars are what we really need to get through. 鈥淓very 300 million years we would expect a gamma-ray burst or a severe supernova explosion that wipes out most of the ozone layer,鈥� says , an expert on intergalactic hazards based at Washburn University in Topeka, Kansas. The result would be a at the Earth鈥檚 surface and an increased incidence of life-threatening cancers during the decades it would take for the ozone layer to recover. It鈥檚 impossible to know when such an event might occur.
Yet these things are so rare that the chance of an extinction event in the next 100,000 years is effectively zero. The same can be said for the threat of a solar flare so powerful that it knocks out all critical infrastructure, because it would take flares 1000 times more powerful than the biggest ever seen. 鈥淐an our sun, in its present state, produce such a flare very occasionally? We don鈥檛 know,鈥� says Mike Hapgood, a solar physicist based at the Rutherford Appleton Laboratory in Oxford, UK, and project manager for the European Space Agency鈥檚 Space Weather Programme. But it remains an unlikely disaster scenario. Which leaves the poster child of disaster movies: the asteroid strike.
This one will take some luck to avoid. Space is full of rocky debris that acts as an occasional threat to Earth. It is widely believed that the impact of a 15-kilometre-wide asteroid wiped out the dinosaurs 65 million years ago. In any 100,000 year period we can reasonably expect an impact from a 400-metre asteroid that will cause damage equivalent to 10,000 megatonnes of TNT. 鈥淣ot enough to do in the whole civilisation, but certainly destroy an entire small country like France,鈥� says former astronaut Thomas Jones, who co-chairs NASA鈥檚 Task Force on Planetary Defence.
鈥淎 400-metre asteroid impact would not be enough to destroy civilisation, but certainly an entire country the size of France鈥�
Some might argue that without France there is little hope for civilisation anyway, but in reality there is only a 1-in-5 chance of total wipeout. 鈥淕lobal effects come from an impact roughly every 500,000 years, so the odds are about 20 per cent for a catastrophic, civilisation-threatening impact within 100,000 years,鈥� Jones says.
We should probably work on some anti-asteroid measures, but really humans concerned about the longevity of our species can relax: the view from here is fine.
