Very high-temperature impact melt products as evidence for cosmic airbursts and impacts 12,900 years ago

Ted E. Bunch, Robert E. Hermes, Andrew M.T. Moore, Douglas J. Kennett, James C. Weaver, James H. Wittke, Paul S. DeCarli, James L. Bischoff, Gordon C. Hillman, George A. Howard, David R. Kimbel, Gunther Kletetschka, Carl P. Lipo, Sachiko Sakai, Zsolt Revay, Allen West, Richard B. Firestone, and James P. Kennett
PNAS published ahead of print June 18, 2012 https://doi.org/10.1073/pnas.1204453109

  1. Edited by* Steven M. Stanley, University of Hawaii, Honolulu, HI, and approved April 30, 2012 (received for review March 19, 2012)

Abstract

It has been proposed that fragments of an asteroid or comet impacted Earth, deposited silica-and iron-rich microspherules and other proxies across several continents, and triggered the Younger Dryas cooling episode 12,900 years ago. Although many independent groups have confirmed the impact evidence, the hypothesis remains controversial because some groups have failed to do so. We examined sediment sequences from 18 dated Younger Dryas boundary (YDB) sites across three continents (North America, Europe, and Asia), spanning 12,000 km around nearly one-third of the planet. All sites display abundant microspherules in the YDB with none or few above and below. In addition, three sites (Abu Hureyra, Syria; Melrose, Pennsylvania; and Blackville, South Carolina) display vesicular, high-temperature, siliceous scoria-like objects, or SLOs, that match the spherules geochemically. We compared YDB objects with melt products from a known cosmic impact (Meteor Crater, Arizona) and from the 1945 Trinity nuclear airburst in Socorro, New Mexico, and found that all of these high-energy events produced material that is geochemically and morphologically comparable, including: (i) high-temperature, rapidly quenched microspherules and SLOs; (ii) corundum, mullite, and suessite (Fe3Si), a rare meteoritic mineral that forms under high temperatures; (iii) melted SiO2 glass, or lechatelierite, with flow textures (or schlieren) that form at > 2,200 °C; and (iv) particles with features indicative of high-energy interparticle collisions. These results are inconsistent with anthropogenic, volcanic, authigenic, and cosmic materials, yet consistent with cosmic ejecta, supporting the hypothesis of extraterrestrial airbursts/impacts 12,900 years ago. The wide geographic distribution of SLOs is consistent with multiple impactors.

Footnotes

  • ↵1To whom correspondence should be addressed. E-mail: tbear1{at}cableone.net.

  • Author contributions: T.E.B., R.E.H., A.M.M., D.J.K., J.H.W., G.K., A.W., R.B.F., and J.P.K. designed research; T.E.B., R.E.H., A.M.M., D.J.K., J.C.W., J.H.W., J.L.B., G.C.H., G.A.H., D.R.K., G.K., C.P.L., S.S., Z.R., A.W., R.B.F., and J.P.K. performed research; T.E.B., R.E.H., A.M.M., D.J.K., J.C.W., J.H.W., P.S.D., J.L.B., D.R.K., G.K., C.P.L., S.S., Z.R., A.W., R.B.F., and J.P.K. analyzed data; and T.E.B., R.E.H., A.M.M., J.H.W., P.S.D., J.L.B., A.W., R.B.F., and J.P.K. wrote the paper.

  • The authors declare no conflict of interest.

  • *This Direct Submission article had a prearranged editor.

  • This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1204453109/-/DCSupplemental.

  • *LeCompte MA, et al., Unusual material in early Younger Dryas age sediments and their potential relevance to the YD cosmic impact hypothesis, XVIII INQUA-Congress, July 21–27, 2011, Bern, Switzerland, paper 1813.

  • †Baker DW, Miranda PJ, Gibbs KE, Montana evidence for extra-terrestrial impact event that caused Ice-Age mammal die-off, American Geophysical Union, Spring Meeting, 2008, abstr P41A-05.

  • ‡Scruggs MA, Raab LM, Murowchick JS, Stone MW, Niemi TM, Investigation of sediment containing evidence of the Younger Dryas Boundary (YPB) Impact Event, El Carrizal, Baja California Sur, Mexico, Geological Society of America Abstracts with Programs, Vol 42, no. 2, p 101 (abstr).

  • §Osinski GF, Bunch TE, Wittke J, Evidence for shock melting of carbonates from Meteor Crater, Arizona, Annual Meeting of the Meteoritical Society, July 28–August 1, 2003, abstr 5070.

  • Buchner E, Schmeider M, Strasser A, Krochert L, Impacts on spherules, 40th Lunar and Planetary Science Conference. March 26, 2009, abstr 1017.

  • ∥Svetsov VV, Wasson JT, Melting of soil rich in quartz by radiation from aerial bursts—A possible cause of the formation for Libyan Desert Glass and layered Australasian tektites, 38th Lunar and Planetary Science Conference. March 13, 2007, abstr 1499.

  • **Petaev ML, Jacobsen SB, Basu AR, Becker L, Magnetic Fe,Si,Al-rich impact spherules from the P-T Boundary Layer at Graphite Peak, Antarctica, 35th Lunar and Planetary Science Conference. March 16, 2004, abstr 1216.

  • ††Buchner E, Schmeider M, Strasser A, Krochert L, Impacts on spherules, 40th Lunar and Planetary Science Conference. March 26, 2009, abstr 1017.

Freely available online through the PNAS open access option.

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Melted glass from a cosmic impact 12,900 years ago
Ted E. Bunch, Robert E. Hermes, Andrew M.T. Moore, Douglas J. Kennett, James C. Weaver, James H. Wittke, Paul S. DeCarli, James L. Bischoff, Gordon C. Hillman, George A. Howard, David R. Kimbel, Gunther Kletetschka, Carl P. Lipo, Sachiko Sakai, Zsolt Revay, Allen West, Richard B. Firestone, James P. Kennett
Proceedings of the National Academy of Sciences Jun 2012, DOI: 10.1073/pnas.1204453109
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