Re-examination of amino acids in Antarctic micrometeorites Original Research Article

The delivery of amino acids by micrometeorites to the early Earth during the period of heavy bombardment (4.5–3.5 Ga) could have been a significant source of the Earthʹs prebiotic organic inventory. Antarctic micrometeorites (AMMs) in the 100–200 μm size range represent the dominant mass fraction of extraterrestrial material accreted by the Earth today. However, one problem is that these `largeʹ micrometeorite grains can be heated to very high temperatures (1000 to 1500 °C) during atmospheric deceleration, causing the amino acids to decompose. In this study, we have analyzed the acid-hydrolyzed, hot water extracts from 455 AMMs for the presence of amino acids using high performance liquid chromatography. For comparison, a 5 mg sample of the CM meteorite Murchison was also investigated. In the Murchison sample we found high levels (∼3–4 parts-per-million, ppm) of α-aminoisobutyric acid (AIB) and isovaline, two non-protein amino acids that are extremely rare on Earth and are characteristic of amino acids of apparent extraterrestrial origin. In contrast, we were unable to detect any AIB above the 0.1 ppm level in the AMM samples studied. Only in one AMM sample from a previous study has AIB been detected (∼300 ppm). To date, more than 600 AMMs have been analyzed for extraterrestrial amino acids. Although our results indicate that less than 5% of all AMMs contain detectable levels of AIB, we cannot rule out the possibility that AIB can be delivered to the Earth intact by a small percentage of AMMs that escaped extensive heating during atmospheric entry.