Abstract
The Sun is (16)O-enriched (Δ(17)O = -28.4 ± 3.6‰) relative to the terrestrial planets, asteroids, and chondrules (-7‰ < Δ(17)O < 3‰). Ca,Al-rich inclusions (CAIs), the oldest Solar System solids, approach the Sun's Δ(17)O. Ultraviolet CO self-shielding resulting in formation of (16)O-rich CO and (17,18)O-enriched water is the currently favored mechanism invoked to explain the observed range of Δ(17)O. However, the location of CO self-shielding (molecular cloud or protoplanetary disk) remains unknown. Here we show that CAIs with predominantly low ((26)Al/(27)Al)(0), <5 × 10(-6), exhibit a large inter-CAI range of Δ(17)O, from -40‰ to -5‰. In contrast, CAIs with the canonical ((26)Al/(27)Al)(0) of ~5 × 10(-5) from unmetamorphosed carbonaceous chondrites have a limited range of Δ(17)O, -24 ± 2‰. Because CAIs with low ((26)Al/(27)Al)(0) are thought to have predated the canonical CAIs and formed within first 10,000-20,000 years of the Solar System evolution, these observations suggest oxygen isotopic heterogeneity in the early solar system was inherited from the protosolar molecular cloud.