Chronology of the Solar System's Oldest Solids

• Published in: The Astrophysical journal 2008-03, Vol.675 (2), p.L121-L124
• Main Authors: Connelly, James N, Amelin, Yuri, Krot, Alexander N, Bizzarro, Martin
• Format: Article
• Language: English
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology
• ISSN: 1538-4357; 0004-637X; 1538-4357
• DOI: 10.1086/533586

Determining the origins of our solar system and, by proxy, other planetary systems, depends on knowing accurately and precisely the timing and tempo of the transformation of the disk of gas and dust to the solids that formed the planets. Relative ages based on the short-lived nuclide super(26)Al indicate that high-temperature calcium-aluminum inclusions (CAIs) formed before lower temperature chondrules but these ages are heavily dependant on a model of homogeneous distribution of super(26)Al within the protoplanetary disk. The competing X-wind model argues for heterogeneous distribution of super(26)Al due to its formation by intra-solar system irradiation such that this system would have no chronological significance. We report a super(207)Pb- super(206)Pb isochron age of 4565.45 plus or minus 0.45 Myr for chondrules from the CV chondrite Allende, an age that is 1.66 plus or minus 0.48 Myr younger than the accepted Pb-Pb age for CAIs from this chondrite group. This age offset is in excellent agreement with the relative ages determined using the super(26)Al- super(26)Mg system, an observation that supports a supernova origin for super(26)Al and, importantly, the chronological significance of the super(26)Al- super(26)Mg system in general. This is consistent with an early and brief CAI-forming event followed by recurrent chondrule formation throughout the life span of the protoplanetary disk. The paucity of old chondrules in chondrite meteorites may reflect their early incorporation into the parent bodies of differentiated meteorites after CAIs were effectively removed from the innermost regions of the protoplanetary disk. Lastly, the agreement between the absolute and relative chronology of CAIs and chondrules requires a solar system age younger than similar to 4567.5 Myr.