Meteoritic dust, material of extra-terrestrial origin, has been identified in two principal forms: spherical particles and irregular, angular particles. Proof of the extra-terrestrial origin of the spherical particles is by chemical analysis, from the fact that their formation cannot be attributed to any known natural terrestrial cause2, by the tendency to obtain higher counts of spherical particles after known meteor showers, and by the occurrence of spherical particles at all times of the year in several widespread localities. The diameters of the particles observed range from about 0.005 mm. up to around 0.2 mm.
Proceedings of the Iowa Academy of Science
©1952 Iowa Academy of Science, Inc.
Thomsen, Warren J.
"The Annual Contribution of Meteoritic Dust to the Mass of the Earth,"
Proceedings of the Iowa Academy of Science, 59(1), 302-306.
Available at: https://scholarworks.uni.edu/pias/vol59/iss1/36