25 February 2012 | NewScientist | 43

Glowing orbs that drift through the air; blue-white sheets of light; sparks and flashes and flames licking up from the ground… all may be signs of disaster to come. For millennia, people have reported strange, baleful lights appearing before and during earthquakes. In 1746, for example, the flames dancing on San Lorenzo Island in Peru impressed prison governor Manuel Romero so much that he briefly released the detainees to let them watch. Three weeks later a huge quake hit nearby Lima and a tsunami washed 5 kilometres inland.

There is plenty of photographic evidence for earthquake lights. They tend to accompany large quakes – with magnitudes above 6 – centred at fairly shallow points in the Earth’s crust. It is not clear how the lights are produced, but Friedmann Freund of NASA’s Ames Research Center in Moffett Field, California, thinks that when rocks in the crust are squeezed, chemical bonds break to produce a pulse of electrical charge that travels up to the surface. “The rocks become like a battery and produce an enormous amount of electric power,” he says.

This process only generates a low voltage, but Freund thinks that the charge forms an ultra-thin layer at the surface. Since the charge is concentrated over a small distance, it would create a strong electric field, perhaps enough to ionise the air and create a luminous discharge that travels up away from the ground – explaining the orbs, flames and aurora-like sheets of light.

Freund does not know why the charge should form such a thin layer, or how the wave of ionisation is maintained for any distance through the air. But experiments are encouraging: crushing rocks in the lab produces electric charge and flashes of light. And low-frequency radio waves have been measured in earthquake zones, suggesting that there are currents underground.

As earthquake lights are so rare, it is hard to show that ionisation and the emission of radio waves coincide with them. Freund has yet to secure funding for a network of cameras and a data-processing centre to monitor such events, but he hopes that such a system, along with satellite imagery, could one day provide earthquake warnings akin to weather forecasts.

Lights may not be the only aerial omens of impending doom. In 2004, a curious linear gap appeared in the clouds above a fault line in Iran. An earthquake followed 69 days later. The gap opened again in 2005, and this time an earthquake followed after six days. Two Chinese geophysicists, Guangmeng Guo and Bin Wang, have suggested that hot gas escaping from the fault might cut through the clouds.

Assuming that humans don’t mess it up completely, Earth’s atmosphere should remain broadly hospitable for many millions of years – but not in the longer term. The sun is slowly getting brighter as its core contracts and heats up. In a billion years it will be about 10 per cent brighter than today, heating the planet to an uncomfortable degree. Water evaporating from the oceans may set off a runaway greenhouse effect that turns Earth into a damp version of Venus, wrapped permanently in a thick, white blanket of cloud. Or the transformation may take some time and be more gentle, with an increasingly hot and cloudy atmosphere able to shelter microbial life for some time.

Either way, water will escape into the stratosphere and be broken down by UV light into oxygen and hydrogen. Oxygen will be left in the stratosphere – perhaps misleading aliens into thinking the planet is still inhabited – while the hydrogen is light enough to escape into space. So our water will gradually leak away.

In 2 or 3 billion years, the oceans will have gone. If volcanoes continue to pump carbon dioxide into the air, Earth may come to resemble Venus even more closely, with a

thick, super-hot CO2 atmosphere. Without ocean water to lubricate Earth’s plate tectonics, the planet could seize up, preventing buried carbon from returning to the air volcanically.

Then we may come to resemble Titan, the giant moon of Saturn, says Jonathan Lunine of Cornell University in Ithaca, New York. Most of Titan is dune-filled desert, just occasionally watered by violent storms of methane rain. Earth could become a warm version of this moon, with a few water-filled lakes at the poles breaking up the vast deserts. The skies will be clear most of the time, but once in a while they will suddenly billow with cloud and pour water onto the parched land. “For a while we’ve still got a lot of water in the atmosphere,” says Lunine. “With a brighter sun there is more energy going into the system, and the potential for very large storms.”

This environment might persist for a hundred million years while the last of the water remains. When it is finally gone, that will be the end of weather as we know it. So the long-range forecast is for cloud, followed by heavy showers, followed by… nothing very much. n

Stephen Battersby is a consultant at New Scientist

” For millennia, people have reported strange, baleful lights appearing before and during earthquakes ”

portents oF doom

Last gasp

120225_F_Strange skies.indd 43 15/2/12 17:49:08