A short timescale for changing oxygen fugacity in the solar nebula revealed by high-resolution 26Al–26Mg dating of CAI rims

Aluminum‐, Calcium‐ and Titanium‐rich Oxide Stardust in Ordinary Chondrite Meteorites

“…A difficulty with this scenario is that a significant number of presolar spinel grains with normal Mg ratios have been modified by isotope exchange, it happened in space prior to accretion into parent bodies, either in the interstellar medium or in the solar nebula. This is supported by observations of calcium-aluminumrich inclusions in meteorites that show Mg isotopic fractionation in their interiors that becomes more normal toward the surface, indicating equilibration with a gaseous reservoir (Caillet Komorowski et al 2007;Fahey et al 1987;Simon et al 2005).…”

Calcium Isotope Composition of Meteorites, Earth, and Mars

“…The CAIs probably formed within 10 5 years of the beginning of MCC and are the oldest known solid materials in the solar system (see Montmerle et al 2006). Chondrules, the distinguishing petrological feature of chondritic meteorites, appear to have formed up to 2 million years after CAI formation (Connelly et al 2008), but possibly less according to Simon et al (2005) and Moynier et al (2007). The mean time of accretion of the Earth is believed to be in the range of 20-40 million years after CAI formation; Mars may have accreted earlier (cf.…”

Response to the Comment by S.B. Simon, L. Grossman, and S.R. Sutton on “Valence state of titanium in the Wark-Lovering rim of a Leoville CAI as a record of progressive oxidation in the early Solar Nebula”

“…Simon et al incorrectly suggest that in earlier work we claimed there was no Ti 3+ in Wark-Lovering rim pyroxenes. In neither the paper by Simon et al (2005) nor the subsequent paper by Dyl et al (2011) did we assert that there was no Ti 3+ in rim pyroxenes. Rather, we found that many pyroxenes have Ti 3+ below detection while others have lower Ti 3+ /Ti 4+ than is typical of CAI interiors, indicating rim formation in a relatively oxidizing environment.…”

“…The fundamental conclusion of the work by Dyl et al (2011) and the earlier study by Simon et al (2005) was not that Wark-Lovering(WL) rims have absolutely no Ti 3+ , as suggested by S. Simon et al, but rather that the Ti 3+ /Ti 4+ ratios of rim pyroxene record oxidizing conditions compared with those attending CAI formation. S. Simon et al evidently disagree with the conclusion that there is lower Ti 3+ /Ti 4+ in rim pyroxenes compared with pyroxenes in the interiors of CAIs, and they suggest there is no evidence in rims for oxidation.…”

“…Rather, we found that many pyroxenes have Ti 3+ below detection while others have lower Ti 3+ /Ti 4+ than is typical of CAI interiors, indicating rim formation in a relatively oxidizing environment. Dyl et al (2011) showed through exhaustive testing that the suggestion by Simon et al (2007) that EMPA data in the paper by Simon et al (2005) were flawed is incorrect. Here we consider each point raised in the comment by S. Simon et al and reiterate that our electron microprobe data and the XANES data of Simon et al (2007) agree and demonstrate a statistically significant ($2r) or greater difference between rim and interior pyroxene Ti 3+ /Ti 4+ .…”