Extraterrestrial dust falls on every part of the Earth, including the parts covered in cities. Most of it arrives as grains a few hundredths to a few tenths of a millimetre across, finer than a grain of sand or close to it, and it lands without anyone noticing. Some of that material can, with effort, [...] The post Earth is quietly dusted with thousands of tonnes of space material every year, most of it as grains smaller than sand — and some of it can be sifted from the grit of ordinary roof gut