Earth and Planetary Science Letters 540, 116266 Link to Article [https://doi.org/10.1016/j.epsl.2020.116266]
1Earth and Planets Laboratory, Carnegie Institution of Washington, 5241 Broad Branch Road, Washington, DC 20015, USA
Interplanetary dust particles (IDPs) and micrometeorites (MMs) were likely major sources of extraterrestrial organics at the surface of the early Earth. However, these particles experience heating to >500 °C for up to several seconds during atmospheric entry. In this study, we aim to understand the effects of atmospheric entry heating on the dominant organic component in IDPs and MMs by conducting flash heating experiments (4 s to 400 °C, 600 °C, 800 °C, and 1000 °C) on insoluble organic matter (IOM) extracted from the meteorite Cold Bokkeveld (CM2). For each of the experimental charges, the bulk isotopic compositions of H, N, and C were analyzed by IRMS, the H isotopic heterogeneities (occurrence of deuterium hotspots) of the samples were measured by NanoSIMS, and the functional group chemistry and ordering of the IOM was evaluated by using FTIR and Raman spectroscopy, respectively. Organic matter in particles heated to ≥600 °C during atmospheric entry experienced significant alteration. Loss of isotopically heavy, labile H and N groups results in decreases in bulk δD, N, H/C and, upon heating ≥800 °C, in N/C. The H isotopic heterogeneity was not greatly affected by flash heating to ≤600 °C, although the hotspots tended to be less isotopically anomalous in the 600 °C sample than in the 400 °C sample. However, the hotspots all but disappeared in the 800 °C sample. Loss of C=O groups occurred at 800 °C. Based on the Raman G-band characteristics, the heating resulted in increased ordering of the polyaromatic component of the IOM.
The data presented in this study show that all aspects of the composition of organic matter in IDPs and MMs are affected by atmospheric entry heating. Modelling and temperature estimates from stepwise release of He has shown that most IDPs and MMs are heated to >500 °C (Love and Brownlee, 1991; Nier and Schlutter, 1993; Joswiak et al., 2007), hence, atmospheric entry heating is expected to have altered the organic matter in most such particles.