I've always assumed that meteorites are quite rare, and as far as ones of any size are concerned that's true. But I was surprised recently to find that thousands of very small "micrometeorites" land on the Earth's surface constantly. Typically they are less than a millimetre in size and weight only a tiny fraction of a gram. If they enter the atmosphere at the right angle and velocity they may suffer some heating but still survive to ground level.
How common are they? Very. A back-of-an envelope calculation suggests that one falls on each square meter about once a fortnight on average. Think of that! You have probably added one to your stock of meteorites during the course of today.
They have been collected in places such as polar regions and in certain geological strata. But finding them in inhabited parts of the world is challenging because of the swarms of other dust-sized particles, many of them of human origin. However recent painstaking research has found undisputed micrometeorites in urban gutters. These are promising sites, because they collect run-off, probably separate out heavier particles (think of panning for gold) and probably trap less contamination from road dust and the like.
If you wanted to find your own, how would you start? First get a neodymium magnet (like the one I mentioned in a previous post about iron in cornflakes, and easily obtained). Put this in a plastic bag and swirl it around in gutter gloop.
Then enclose this in another plastic bag, and pull the magnet out of the inner bag. Voila! Candidate particles will have been collected between the bags.
Now comes the hard part. Almost all will be metallic grains created by human activity. So you will have to examine your finds under a microscope and carefully pick out the stardust. Not at all easy, but luckily there is a book by a dedicated enthusiast.
Read more here about Project Stardust
Images from here
micro-meteoritesVery interesting, wonder how much mass the micro-meteorites add to the earth per year.
About 100 tonnes per day perhaps. But it's awfully hard to measure.
The Earth is probably not getting heavier overall though, because H and He are lost from the atmosphere (their average molecular velocity exceed escape velocity). See
Thanks for the link. I'm happy we are losing the some of the boring light gases and gaining some interesting heavy elements.