Cosmic threats, like the flare-up 2 million years ago of the Milky Way's black hole, are a reminder that humanity’s survival is up to us
TWO million years ago, something not quite human looked up at the sky and saw a glowing light, about the size of the moon, that hadn't been there before. That light was a huge eruption at the black hole at the centre of our galaxy, according to new research by astronomers.
We can only make educated guesses at what our predecessors would have made of this strange sight, which took place long before recorded history. We're not even sure which species of hominin might have been looking (see "Early humans saw black hole light in the night sky
We might take it as further evidence of the precariousness of our existence: how the universe teems with threats, some still unsuspected, that might wipe us out in an instant. Had our planet orbited a star closer to the Milky Way's black hole, it would have been bathed in radiation – probably killing off our ancestors.
Cosmic radiation, which might also come from a supernova, is one of the few scenarios that could wipe out life on Earth, although bacteria might survive even that (see "DNA-grabbing bacteria hint at early phase of evolution"). Perhaps that's far-fetched; but then again, we don't know how many worlds out there may have been sterilised by abrupt cosmic events.
But what significance do such threats hold for our quotidian existence? After all, we can't do much about erupting black holes. But think on: if Earth were emptied of life, it would be emptied of much more besides. In fact, the planet would eventually be transformed beyond recognition, becoming a hellish grey rock (see "Lifeless Earth: What if everything died out tomorrow?").
That scenario really is far-fetched – even the gloomiest eco-worrier need not lose sleep over it. But it does highlight how closely intertwined our planet's geology and biology are. And it is that intertwining that we humans are picking at with our continuing assaults on the environment.
Despite the toll we're taking on the Earth's other inhabitants, the threat here is not ultimately to the planet, or even its biosphere. It's to us. Subtract humans, and after not too long the planet would carry on much as before (New Scientist, 14 October 2006, p 36).
These threats, unlike the cosmic perils, are tractable. We can try to sort out the mess we've made. Or settle other planets to help ensure our species' survival. In the face of a pitiless universe and indifferent planet, human survival is of concern only to humans. Unlike our ancestors, we can do more than just look on in bafflement.
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