Finally, scientists have solved a cosmic riddle — what happens to the tons of dust particles that hit the Earth every day. The answer: Nothing, because the tiny flecks are everywhere.
An international team found that rooftops readily collect the extraterrestrial dust, contrary to science authorities who discarded the idea as little more than an urban myth.
As he puts it, “To pick out one extraterrestrial particle among billions of others requires knowledge both about what to look for and what to disregard.”
The tiny flecks have hit the Earth for billions of years. Known as micrometeorites, they rain down on the planet continuously, but have proved remarkably hard to find. Some bits are so small and lightweight that they drift down to the Earth’s surface without melting.
The dust consists of tiny remnants from the solar system’s birth, including debris from the lumps of dirty ice known as comets and from collisions between planets and asteroids. While most of the particles are interplanetary in nature, some even contain grains of matter from outside the solar system, which then makes it truely stardust.
Matthew J. Genge, one of the paper’s authors, used an electron microprobe to determine the chemical makeup of Mr. Larsen’s finds and confirm their cosmic origin.
In an interview, he said that, over all, the grains that survive the atmospheric plunge and land on the Earth’s surface add up to more than 4,000 tons annually, or more than 10 tons a day. “Larsen has done a valuable thing in classifying the contaminants,”
“I consider my microscope a telescope,” Genge said. “It can give you a pretty big picture.”
 Genge, Larse, Van Ginneken, Suttle: An urban collection of modern-day large micrometeorites: Evidence for variations in the extraterrestrial dust flux through the Quaternary in Geology - 2017