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Rare meteorites common in the Ordovician period


Most meteorites that fall today are H and L type ordinary chondrites, yet the main belt asteroids best positioned to deliver meteorites are LL chondrites1,2. This suggests that the current meteorite flux is dominated by fragments from recent asteroid breakup events3,4 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 ago5. 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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Figure 1: Micrometeorite-bearing limestone beds at the Lynna River section in northwestern Russia that were deposited around 466 million years ago.
Figure 2: Values of Δ17O and TiO2 of our data compared with compositions of different relevant meteorite groups.
Figure 3: Probability density functions (PDFs) of Δ17O values showing the distribution of different micrometeorite categories.


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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.

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Authors and Affiliations



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.

Corresponding author

Correspondence to Philipp R. Heck.

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The authors declare no competing financial interests.

Supplementary information

Supplementary Information

Supplementary Figures 1 and 2, Supplementary Table 1, description of Supplementary Data files. (PDF 284 kb)

Supplementary Data 1

Data table with Δ17O, TiO2 and V2O3 values and classification of fossil micrometeorites. (XLSX 15 kb)

Supplementary Data 2

Chrome spinel abundances in different types of meteorites. (XLSX 46 kb)

Supplementary Data 3

Reference data. (XLSX 55 kb)

Supplementary Data 4

Full data table with O-isotopic SIMS data and quantitative elemental EDS data. (XLSX 19 kb)

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Heck, P., Schmitz, B., Bottke, W. et al. Rare meteorites common in the Ordovician period. Nat Astron 1, 0035 (2017).

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