Why humans must leave Earth

Why send astronauts to other worlds? After all, some would argue that robots are far better suited to the extremes of space. Automated probes offer a cheaper and safer way to explore the solar system, they say - just look at the success of NASA's Mars Rovers and the Huygens probe on Titan. Such missions justify their expense by the boost they provide to human knowledge.

By contrast, proponents of human exploration invoke a more romantic argument: the human spirit's desire to tread new land, see new sights or climb virgin peaks, simply "because they are there". Yet there is a more compelling reason to send people. It comes down to a single word: survival.

If we remain on Earth we will surely become extinct, and probably long before an expanding Sun roasts our planet. The fact is that we are vulnerable to the same types of catastrophic events that have wiped out other species on Earth. Geological history shows that such extinction events are routine.

Tyrannosaurus rex lasted only a few million years. Mammalian species, on average, last just a couple of million years. Our parent species, Homo erectus, lasted about 1.6 million years, while Neanderthals died out after only 300,000 years. We might have conquered the planet but it is just a tiny island in the universe, and species confined to a single island are often found on the endangered list.

The problem is that it is hard to justify the huge expenditure of sending colonists into space - probably hundreds of billions of dollars - when we do not know when catastrophe will strike. One thing is certain: about 5 billion years from now, the sun will have swelled up to form a red giant. While this bloated sun may not actually engulf our planet it will certainly fry it. Yet we will most likely die out long before then. An asteroid or comet strike could cause mass extinctions, as could runaway climate change. Avian flu, AIDS, Ebola, Malaria, TB and Smallpox also loom, to say nothing of the possibility of a new virus emerging to infect and kill everyone before we know enough about it to respond.

While it is well known that we pose a danger to other species - just ask the passenger pigeon - it is not a great leap of reasoning to realise that we also pose a danger to ourselves. Nuclear war, bioterrorism or even nanotechnology gone wrong may yet kill us off. Intelligence of the kind we have, with our aptitude for abstract reasoning and the ability to discern our place in the universe may turn out to be, as biologist Stephen Jay Gould said, just "one bauble on the Christmas tree of evolution". What's more, Darwin tells us that species usually do not live up to their potential, not least because most species do not leave descendant species.

Read page two.

Published on 30 October 2007

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