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| At right, the star before supernova. At left, the cataclysm. |
What would happen to our region of space if a star as nearby as, say, Sirius, were to reach the end of its life cycle and explode in a cataclysmic supernova? The explosion would flood this region of space with a heavy flux of cosmic radiation. The effects for life on Earth might well be devastating.
David Schramm and John Ellis say that radiation from an exploding star could destroy the Earth's ozone layer for hundreds of years, leaving phytoplankton and plants unprotected against ultraviolet light. Then "our own sun does the killing" - as if the ozone hole now over Antarctica suddenly expanded to cover the globe - and the food chain crumbles from the bottom up.
Using new data on nearby supernovae, Schramm and Ellis also note an interesting coincidence between their best guess for local supernovae rates - one event every few hundred million years - and the age of the granddaddy of all mass extinctions: the one that ended the Permian period some 185 million years before the dinosaurs bit the late-Cretaceous dust.
Clearly not every mass extinction is due to nearby supernovae. For example, the Cretaceous-Tertiary (K-T) event has been studied intensively. A census of marine mollusks shows that those which consume plankton were no worse off than other mollusks as a result of the K-T event.
Of course, if the mass extinction at the end of the Permian shows evidence consistent with a nearby supernova, its timing, some 250 million years ago, places us in range for another event of this type, any time in the next few million years. That event could already have taken place some lightyears away from Earth, with the wave front travelling toward us at the speed of light to reach us in the next few years. Or that event might be hundreds or millions of years in our future.
How do we defend ourselves and our sort of life from such an event? Obviously, being stuck on a single planet orbiting a single star is not going to be especially effective. Even if we become a multi-planetary species, humanity is still at risk from extinction. Only by having multiple solar systems at our disposal will we achieve any degree of protection from nearby supernovae, by having some of our species and related life forms on a distant planet or space habitat orbiting a star sufficiently distant to have a negligible effect from the supernova.
To become a multi-planetary species is certainly the work of some decades; to become a multi-stellar species is the work of some centuries. Spanning a large enough sector of the galaxy to be reasonably secure from supernovae may be the work of millennia.
The longest journeys begin, just as the shortest ones, with a single step.
