Isotopic fractionation of iron, potassium, and oxygen in stony cosmic spherules: Implications for heating histories and sources

3He, 20,21,22Ne, 14C, 10Be, 26Al, and 36Cl in magnetic fractions of cosmic dust from Greenland and Antarctica

“…Evidence for heating (e.g., Taylor et al 2005;Flynn 1989Flynn , 1995Flynn , 2001) might also support this hypothesis. Since our radionuclide results appear consistent with P-R lifetimes, we favor the conclusion that the data are consistent with the magnetic particles having been released in space from the break-up of meter-sized or larger meteoroids in space ~2-4 × 10 5 years ago and intercepted by the Earth.…”

“…We obtained samples of micrometeorite debris from the SPWW, described in detail by Taylor et al (1998Taylor et al ( , 2000Taylor et al ( , 2005Taylor et al ( , 2007. Taylor et al (2000) estimated micrometeorite influx rates from cosmic spherules in SPWW and estimated an accretion rate of 1100 ± 200 tons/yr for particles in the 50-300 μm size range.…”

Microtexture, nanomineralogy, and local chemistry of cryptocrystalline cosmic spherules

“…However, the FeNi droplets might also be of secondary nature and be pro duced in the spherules via the reduction of these ele ments in silicates when the micrometeoroid flew through the upper rarefied atmospheric layers of the Earth (Brownlee et al, 1997;Taylor et al, 2005). This hypothesis is underlain by the fact that the cryptocrys talline and barred spherules have the same Mg/Si ≈ 1, but the material of the former often hosts metal droplets and is richer in Fe than that of the barred spherules, which typically bear no metal.…”

“…Some of the spherules are "iron" and are made up of Ni bearing magnetite and wustite and often contain Fe-Ni metal cores. A cosmic origin of the spherules follows from their Ni and Ir con centrations (Brownlee et al, 1984), their oxygen isoto pic composition (Clayton et al, 1986;Taylor et al, 2005;Yada et al, 2005;Engrand et al, 1998), the pres ence of taenite and/or kamacite, and from similarities between their composition and those of chondrites (except only very rare eucrite CS). For example, the bulk composition of most of the silicate spherules define a clear cut compositional trend in the Mg-Fe-Si dia gram, with this trend showing a typical "solar" Mg/Si ratio close to 1, which is typical of chondrites.…”

“…and mildly volatile (Fe, Mg, and Si) elements and their compounds and with redox reactions changing the valence of Fe (Brownlee et al, 1997;Taylor et al, 2005;Cordier et al, 2011). In interpreting data on the com position of cosmic spherules, it is important to under stand as to how much the chemical composition of the spherules and variations in this composition reflect the chemistry of the solid precursors (micrometeorites) and how much the compositional variations may be indica tive of changes in the composition of the solid precur sors during their melting in the Earth's atmosphere.…”