What would a death star do to Earth?
Gamma-ray bursts – or death stars – are the most violent events in the Universe. Robert Matthews asks if we've already been devastated by one, and what an explosion would do to us in the future.
Did a death star previously obliterate life on Earth?
Around 450 million years ago, the Earth was devastated by a terrible disaster that annihilated around 85 per cent of all marine species – at the time, the predominant form of life on the planet.
Known as the Late Ordovician Extinction, it was the second most devastating blow to life on Earth during its history – worse even than the notorious impact-related event that forced the dinosaurs into extinction 65 million years ago. Geological evidence points to a sudden plunge in global temperatures, though the cause remains uncertain. But one possibility is the explosion of a death star relatively close to Earth.
Analysis of the effects of a gamma-ray burst by researchers at the University of Kansas and the US space agency NASA suggests it would have triggered the destruction of the Earth’s protective ozone layer, allowing intense ultraviolet radiation from the Sun to reach the surface. This would have wiped out many life-forms in the upper layers of the oceans – including plankton, a key part of the marine food chain. It’s also possible that the changes in atmospheric chemistry triggered by the blast may, in turn, have triggered global cooling – though whether this would be enough to account for the Ordovician ice age is unclear.
What is certain is that giant stars capable of producing gamma-ray bursts are spread throughout the cosmos. As such, it is not only life on Earth that’s threatened by them. According to research by Professor James Annis of the Fermi National Accelerator Laboratory, Illinois, gamma-ray bursts may regularly sterilise their host galaxies; if that’s true, our chances of finding life elsewhere in the Milky Way would be much reduced.
What a death star explosion would do to Earth...
Such is the power of a death star explosion that even from a distance of several thousand lightyears, the effects would be devastating for life on Earth.
But the threat isn’t from radiation sickness triggered by the gamma-rays: these would be absorbed by the atmosphere. It’s the effect of the rays on the gases in the atmosphere that poses the real risk to life. Nitrogen and oxygen molecules would be blasted apart by the radiation – forming nitrogen dioxide, a toxic brown gas that would attack the ozone layer, which shields the Earth from deadly ultraviolet radiation from the Sun.
As the nitrogen dioxide spreads, large areas of the atmosphere become darker, driving down global temperatures. At the same time, the gas would combine with rain and seawater, producing nitric acid. Assailed by both intense ultraviolet radiation and acid, life-forms unable to find shelter at least 10 metres below the surface of the Earth’s oceans would be at grave risk from radiation and chemical burns, and longer-term threats including mutations, sterility and death. The decline in global temperatures may also disrupt ocean currents, altering the distribution of heat around the Earth, and potentially triggering a global ice age.
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It takes several years for the Earth to begin to recover from the effects of the death star blast. The dark, toxic nitrogen dioxide gradually washes out of the atmosphere as rain. No longer attacked by the gas, the ozone layer starts to recover and the levels of ultraviolet radiation reaching the surface of the Earth starts to fall. At the same time, the atmosphere begins to clear, allowing global temperatures to climb.
Some species of organism actually benefit from the fertilising effect of the nitrogen-rich compounds descending from the atmosphere, and start to thrive. Surviving life-forms begin to move into the ecological niches left by those destroyed by the blast.