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What are micrometeorites?
The short answer
Micrometeorites are basically micrometeoroids that have survived entry through Earths atmosphere.
Origins
Most micrometeorites come from comets but a very small percentage come from asteroids. This distinguishes micrometeorites from the meteorites you are used to seeing because most meteorites do indeed come from asteroids.
Flux
We are consistently bombarded by these little specks of cosmic dust at a rate of about 30,000 tons/year and we can find them on the ground and on roofs at about 1 micrometeorite per square meter per year. So they are all around us and we only need to find the best methods to search for them.
A brief history
Micrometeorites have been found everywhere...
At the South Pole from a water well where scientists get their drinking water, and recently 30,000-50,000 have been found along mountain ridges in the Antarctic as well.
They have been found at the bottom of the sea.
In 1872 scientists aboard the Challenger discovered little metal spheres and concluded that they were not likely man made.
And now in urban areas
It is only very recently that we have been able to find micrometeorites in urban areas, this was once thought impossible.