Reading this outside? Beware of incoming ‘micrometeorites’

No pollution reaches Concordia station, 3200 metres up in the Antarctic. Neither does much snow – just a few centimetres a year. But there is something else, strewn among the ice. Tiny particles of smooth, oddly glassy dust.

They don’t come from the clouds and, in the middle of an ice cap, they can’t have come from the land, so there is only one other source: space. Scientists have counted them, to estimate that across the Earth this dusting of ‘‘micrometeorites’’ accounts for 5000 tonnes of rock a year – far more than arrives in visible meteorites. The Earth is constantly bombarded by meteorites. Most are smaller than this full stop. That makes them almost impossible to find. They are, though, important for our understanding of life on Earth. The meteorites bring complex organic molecules of the kind needed, for instance, for DNA. They are cosmic wanderers, as old as the solar system, that tell us about the time of its creation.

As they enter the atmosphere, about two thirds of their mass evaporates. ‘‘This gives rise to layers of metal atoms and ions,’’ said John Plane, professor of atmospheric chemistry at Leeds University. ‘‘They stop radio communications with space, or cause anomalous reflections.’’

As the particles drift down through the atmosphere, they oxidise and form nucleation points for clouds.

Micrometeorites were first identified 150 years ago in the Indian Ocean. The scientific ship HMS Challenger dredged up a vast amount of whale bones. Its crew concluded that either ‘‘whales so abounded in the sea at one time as to cover the floor of the ocean with a continuous stratum of their remains’’ or, more likely, there was almost no sedimentation. Among the bones were ‘‘numerous minute spherular particles of metallic iron’’. They deduced that the spherules came from space.

Plane, whose research is published in the journal Earth and Planetary Science Letters, says the ‘‘pristine’’ environment of Concordia makes it easier to study the particles. The only substance there that isn’t water is micrometeorite.