Numbers, types, and compositions of an unbiased collection of cosmic spherules

Details Numbers, types, and compositions of an unbiased collection of cosmic spherules Numbers, types, and compositions of an unbiased collection of cosmic spherules

Jul 2000

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000m%26ps...35..651t&link_type=abstract

Meteoritics & Planetary Science, vol. 35, no. 4, pp. 651-666 (2000).

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Scientific paper

Micrometeorites collected from the bottom of the South Pole Water Well (SPWW) may represent a complete, well-preserved sample of the cosmic dust that accreted on Earth from 1100-1500 AD. We classified 1588 cosmic spherules in the size range 50-800 μm. The collection has 41% barred olivine spherules, 17% glass spheres, 12% cryptocrystalline spherules, 11% porphyritic olivine spherules, 12% relic grain-bearing spherules, 3% scoriaceous spherules, 2% I-type spherules, 1% Ca-Al-Ti-rich (CAT) spherules and 1% G-type spherules. We also found bubbly glass spherules, spherules with glass caps, and ones with sulfide coatings, particles that are absent from other collections. A classification sequence of the stony spherules (scoriaceous, relic grain bearing, porphyritic, barred olivine, cryptocrystalline, glass, and CAT) is consistent with progressive heating and evaporation of Fe from chondritic materials. The modern-day accretion rate and size distribution measured at the SPWW can account for the stony spherules present in deep-sea collection through preferential dissolution of glass and small stony spherules. However, weathering alone cannot account for the high accretion rate of I-type spherules determined for two deep-sea collections. The SPWW collection provides data to constrain models of atmospheric-entry heating and to assess the effects of terrestrial weathering.

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