Rare meteorites common in the Ordovician period

  • Nature Astronomy 1, Article number: 0035 (2017)
  • doi:10.1038/s41550-016-0035
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Most meteorites that fall today are H and L type ordinary chondrites, yet the main belt asteroids best positioned to deliver meteorites are LL chondrites 1,2 . This suggests that the current meteorite flux is dominated by fragments from recent asteroid breakup events 3,4 and therefore is not representative over longer (100-Myr) timescales. Here we present the first reconstruction of the composition of the background meteorite flux to Earth on such timescales. From limestone that formed about one million years before the breakup of the L-chondrite parent body 466 Myr ago, we have recovered relict minerals from coarse micrometeorites. By elemental and oxygen-isotopic analyses, we show that before 466 Myr ago, achondrites from different asteroidal sources had similar or higher abundances than ordinary chondrites. The primitive achondrites, such as lodranites and acapulcoites, together with related ungrouped achondrites, made up ~15–34% of the flux compared with only ~0.45% today. Another group of abundant achondrites may be linked to a 500-km cratering event on (4) Vesta that filled the inner main belt with basaltic fragments a billion years ago 5 . Our data show that the meteorite flux has varied over geological time as asteroid disruptions create new fragment populations that then slowly fade away from collisional and dynamical evolution. The current flux favours disruption events that are larger, younger and/or highly efficient at delivering material to Earth.

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The study was supported by an ERC-Advanced Grant (ASTROGEOBIOSPHERE) to B.S. P.R.H. acknowledges funding from the Tawani Foundation. A.D. acknowledges support from the Russian Governmental Program of Competitive Growth of Kazan Federal University and RFBR (grant 16-05-00799). W.F.B’s participation was supported by NASA’s SSERVI program “Institute for the Science of Exploration Targets (ISET)” through institute grant number NNA14AB03A. We thank K. Deppert and P. Eriksson for support at Lund University, F. Iqbal for the laboratory work, and B. Strack for maintenance of the Field Museum’s SEM laboratory. WiscSIMS is partly supported by the National Science Foundation (EAR03-19230, EAR13-55590). We thank J. Kern for SIMS support. The 3D microscopy was performed in the Keck-II facility of the Northwestern University NUANCE Center, supported by NSEC (NSF EEC–0647560), MRSEC (NSF DMR-1121262), the Keck Foundation, the State of Illinois and Northwestern University.

Author information


  1. Robert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, Illinois 60605, USA

    • Philipp R. Heck
    • , Birger Schmitz
    •  & Surya S. Rout
  2. Chicago Center for Cosmochemistry and Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USA

    • Philipp R. Heck
    •  & Surya S. Rout
  3. Astrogeobiology Laboratory, Department of Physics, Lund University, PO Box 118, SE-22100 Lund, Sweden

    • Birger Schmitz
    • , Anders Cronholm
    •  & Fredrik Terfelt
  4. Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, Colorado 80302, USA

    • William F. Bottke
  5. WiscSIMS, Department of Geoscience, University of Wisconsin-Madison, 1215 W. Dayton Street, Madison, Wisconsin 53706-1692, USA

    • Noriko T. Kita
    •  & Céline Defouilloy
  6. Geological Institute, Russian Academy of Sciences, Pyzhevsky Pereulok 7, 119017 Moscow, Russia

    • Andrei Dronov
  7. Kazan (Volga Region) Federal University, Kremlevskaya ulitsa 18, 420008 Kazan, Russia

    • Andrei Dronov


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P.R.H. and B.S. conceived the study and wrote the paper with input from all authors. W.F.B. provided expertise on the collisional and dynamical evolution of the asteroid belt and meteoroid delivery models. B.S., F.T. and A.D. conducted the fieldwork. B.S., F.T. and A.C. extracted and prepared the samples for SEM/EDS and SIMS. A.C. performed the quantitative SEM/EDS analysis. P.R.H. and S.S.R. prepared the samples for SIMS and performed the SIMS and post-SIMS analyses. N.T.K. and C.D. set up SIMS analysis conditions and assisted with the analyses.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Philipp R. Heck.

Supplementary information

PDF files

  1. 1.

    Supplementary Information

    Supplementary Figures 1 and 2, Supplementary Table 1, description of Supplementary Data files.

Excel files

  1. 1.

    Supplementary Data 1

    Data table with Δ17O, TiO2 and V2O3 values and classification of fossil micrometeorites.

  2. 2.

    Supplementary Data 2

    Chrome spinel abundances in different types of meteorites.

  3. 3.

    Supplementary Data 3

    Reference data.

  4. 4.

    Supplementary Data 4

    Full data table with O-isotopic SIMS data and quantitative elemental EDS data.