containing the first abundant L chondrites is large enough to assess the pre-LCPB flux. The interval sampled represents a time average of about 10 to 100 kyr and was selected with the aim of determining whether the composition of the meteorite flux to Earth was similar to or different from that of today. This is the first reconstruction of the background flux of the different meteorite types in a geological time perspective. Similar reconstructions are ongoing for other periods in the Earths geological past 10 .Additional informationHow to cite this article: Heck, P. R. et al. Rare meteorites common in the Ordovician period. Nat. Astron. 1, 0035 (2017).AcknowledgementsThe 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.Bs participation was supported by NASAs 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 Museums 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 EEC0647560), MRSEC (NSF DMR-1121262), the Keck Foundation, the State of Illinois and Northwestern University.Author informationAffiliationsRobert A. Pritzker Center for Meteoritics and Polar Studies, The Field Museum of Natural History, 1400 South Lake Shore Drive, Chicago, Illinois 60605, USAPhilipp R. Heck, Birger Schmitz & Surya S. RoutChicago Center for Cosmochemistry and Department of the Geophysical Sciences, The University of Chicago, 5734 South Ellis Avenue, Chicago, Illinois 60637, USAPhilipp R. Heck & Surya S. RoutAstrogeobiology Laboratory, Department of Physics, Lund University, PO Box 118, SE-22100 Lund, SwedenBirger Schmitz, Anders Cronholm & Fredrik TerfeltDepartment of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, Colorado 80302, USAWilliam F. BottkeWiscSIMS, Department of Geoscience, University of Wisconsin-Madison, 1215 W. Dayton Street, Madison, Wisconsin 53706-1692, USANoriko T. Kita & Celine DefouilloyGeological Institute, Russian Academy of Sciences, Pyzhevsky Pereulok 7, 119017 Moscow, RussiaAndrei DronovKazan (Volga Region) Federal University, Kremlevskaya ulitsa 18, 420008 Kazan, RussiaAndrei DronovContributionsP.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 interestsThe authors declare no competing financial interests.Corresponding authorCorrespondence to Philipp R. Heck.FREE PDF GRATIS: Nature Astronomy Sup. Info.PDF files1. Supplementary Information Supplementary Figures 1 and 2, Supplementary Table 1, description of Supplementary Data files.Excel files1. Supplementary Data 1 Data table with 17O, TiO2 and V2O3 values