Asteroid breakup linked to Great Birger Schmitz Bernhard PeuckerEhre - PDF document

1 Asteroid breakup linked to Great Birger
Asteroid breakup linked to Great Birger Schmitz, Bernhard Peucker-EhrenbrinkCarl Alwmark, Mario Tassinari and Wang *e-mail: birger.schmitz@geol.lu.se The rise and diversification of shelled invertebrate life in the early Phanerozoic took place in two major steps. During large number of new phyla appeared over the family, genus and species level, however, remained low until the Great t (GOBE) in the mid-Ordovician1-3represents the most intense phase of species radiation during the Paleozoic and the biological component of planet's seafloors was irreversibly changed. The causes of the GOBE remain elusive mainly relating faunal to environmental change. Here we show that the onset of the a. 470 Ma with the disruption in the asteroid belt of the L chondrite parent body, the largest documented asteroid breakup event during the last few billion years4-6between an event in space and on Earth is established by bed-by-bed records of extraterrestrial chromi

2 te, osmium isotopes and invertebrate fos
te, osmium isotopes and invertebrate fossils in mid-Ordovician strata in Baltoscandia and ChEarth of kilometer-sized asteroids accelerated the biodiversification. This is Department of Geology, University of Lund, Sölvegatan 12, SE-22362 Lund, Sweden.History Museum of Denmark, Geological Museum, University of Copenhagen, Øster Voldgade 5-7, DK-1350 Copenhagen K, Denmark. Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, MS 25, Woods Hole, MA 02543, USA. School of Earth Sciences, The Ohio State University, 125 South Oval Mall, Columbus, OH 43210, USA. Yichang Institute of Geology and Mineral Resources, Yichang, Hubei 443003, China. Evidence for an early Paleozoic major ases of the L type were shown to have 4-6meteorites reaching Earth today are shocked L chondrites from this event. The finds of more than 50 fossil L chondritic meteorites (1 to 20 cm in diameter) in Middle Ordovician limestone in souther

3 n Sweden show that the meteorite flux wa
n Sweden show that the meteorite flux was enhanced by one to two orders of magnitude for at least a few million years after the disruption 7,8. The L chondritic origin of the fossil meteorites is demonstrated by element and oxygen isotope analyses of relict chromite7-9. Chromite is the only common mineral in chondrites that survives extensive weathering on the wet Earth surface. In the limestone beds chromite grains from decomposed micrometeorites are found10-12. Cosmic-ray induced Ne in chromite from the fossil meteorites increases upward inon origin from an asteroid Ar dating of recent L chondrites has constrained the timing of their parent-body dibeds with fossil meteorites according to the latest geologic time scaleDuring the GOBE, in the mid to late Ordovician, biodiversity at the family level increased from a Phanerozoic all-time-low in the Cambrian and early Ordovician to levels approximately three times higher in the late Ordovician1-3,15

4 ,16 (Fig. 1). The of marine life were m
,16 (Fig. 1). The of marine life were matched by an increase in biocomplexity, ozoic except for short-term declines in latest Ordovician and late Devonian. The l among a wide variety of groups of skeletal 2,3,16. Diagrams of changes in global GOBE only give a crude representation of the timing and pace of the faunal 16,17ination of many regional diversity 2,3. The most focused global compilation at about the Arenig-Llanvirnnumber of groups, such as the brachiopods, cephalopods and echinoderms, but less clear in some members of the Cambrian nd the Modern fauna . The causes of the GOBE, and its relation to both intrinsic (biological) and extrinsic (envir. Many authors have levels of atmospheric oxygen,aerobic metazoan life together with an19,20 Although biodiversity diagrams such as the effects of poor correlation and poor preservation of faunas, "monographic bursts", and data binning. In order to relate biological change to physical events, det

5 ailed high-resolution, multiparameter re
ailed high-resolution, multiparameter records across complete and fossil-risediment-dispersed extraterrestrial (chondritic) chromite (EC) grains and Os isotopic studies in mid-Ordovician sections with condensed limestone (Fig. 2). These results are matched by the so far most detailed bed-brachiopod species across mid-Ordovician 350 km apart in southern Sweden, and at ang, Hubei province. The EC grai�ns (63 limestone samples that were dissolved in from terrestrial chromite by its distinct element composition7,11. The results of the EC searches are shown in Fig. 2 and in the Supplementary Information. In the Kinnekulle, in 379 kg of limestone from 14 levels across 9 m of strata below the Zone only 5 EC grains were found (Fig. 2). The values then increase dramatically to typically 1-zones. In this interval a similar to that at Kinnekulle. In southern Scania some beds in the 125 kg in the beds spanning 7 m belowChinese sections, 89 kg of lime

6 stone below the grain compared to 117 EC
stone below the grain compared to 117 EC grains in The first appearance of common EC grains in the lower timing of the disruption of the L flux of micrometeorites to 10-12There is no indication that changes in sedimentation rates, on average a few millimeter ved major trend in EC concentrations, although individual beds may have formed at Zone is consistent with cosmic-ray induced ages of chromite grains from the fossil meteorites. In 5-10 million years younger condensed limestone in the Gärde quarry, cethe EC flux is still enhanced compared to that before the ations of EC grains are similar to concentrations measured in similarly condensed sediments from much younger periods. For example, in 210 kg of pelagic limestone (average sedimentation rate ca. ) from the famous late Cretaceous-Paleocene Gubbio section in Italy we The results from our analyses of Os in whole-rock limestone samples through the lower 11 m of section, but from the same bed

7 where the EC grains become common and up
where the EC grains become common and upwards, ratios mainly lie in the range 0.3-0.5 (Fig. 2; Supplementary Information). The simplest explanation for this prominent change is an increasing 187Os ~0.12) at the expense of a detrital/hydrogenous Os component (Some of the best sections for studies ofoccur in Baltoscandia. We have established the mid-for brachiopods based on bed-by-bed sampling of more than 30,000 fossils from eight um Brachiopoda dominated the benthos of bundance and diversity and formed a pivotal ns of the era. The phylum was widely dispersed across shallow to deep-water eWe show here that there are two intervals in the succession when the Baltoscandian brachiopod fauna suffered dramatic changes - one within the lower part of the regional Kunda Stage (Fig. 3). The largest change occurs during exactly the same interval when the L chondritic extraterrestrial flux and when brachiopods more typical of the ides and strophomenides, dive

8 rsified. of extraterrestrial matter, in
rsified. of extraterrestrial matter, including large asteroids, during 10-30 million years after major asteroid disruption events created the Flora family of asteroids. These asteroids were particularly because of their position relative to an important orbital resonance24,25mid-Ordovician interval with ethe main phase of the GOBE1-3,16. At least in Baltoscandia the onset of the two events Albeit speculative, the best explanation for the coincidence is that frequent impacts on Earth of large asteroids, fragments of the L e biota. Impact related environmental perturbations may have accelerated a process driven also by intrinsic biological mechanisms. Although much contemporary effects of large impacts, such as , more minor and persistent impacts could generateniches across a mosaic of more heterogeneous environments. Such diversity increases lished Intermediate Disturbance Hypothesis, initially l reefs and tropical rain forests. Frequent impacts

9 may also have destabilized ecological co
may also have destabilized ecological communities, allowing invasive species to take over and displace incumbent communities. The ecological and taxonomic amplitudes of the mid-Ordovician biodiversification may be decoupled and there are important feedback loops in the procersification is marked by a brachiopod takeover from trilobites in benthic communities, and the establishment of recumbent life modes and size increases in many brachiopod clades. However, in was now dominated by a suspension-feeding benthos with low metabolic rates better om major environmental disruptions. There are about 170 known impact craters impacts may have been more common by a fg the mid-Ordovician compared to other periods of the Phanerozoic7,14. Four of seventeen known impact of Earth's craters has it been possible to determine the impactor type, but for at leSweden chromite in resurge deposits has implicated an L chondritic impactorThe strata in China and Baltosca

10 ndia that we show are rich in fossil met
ndia that we show are rich in fossil meteorites Over several hundred thousand square kilometers in southern Sweden the succession of homogeneous red orthoceratite limestone is interrupted by a one-meter thick anomalous grey, clay-rich intecm-sized cystoids appear to have literally covered the sea floor of a major part of the Baltic Basin. In west Russia peculiar ooid-horizons characterize the interval, and in China unusual mini-mounds interrupt the normal succession of nodular marl and limestoneomalous lithologies and impacts or other astronomical peher studies. As shown here, at least on a regional scale, there is a close temporal coincidence between major biological change Recently the impactor at the Cretaceous-Tertiary boundary has been tied by , but this event may not have led er as focused in time as the one in the mid-Ordovician, signal in the collision history of present-day meteorites. For chromite searches, samples of typically 10-30

11 kg of limestone were crushed and decalc
kg of limestone were crushed and decalcified first in 6 M HCl and then in 18 M HF at room temperature. The acid-m, was searched for opaque minerals under the binocular microscope. Picked grains were mounted in epoxy resin and polished to a flat surface m diamond slurry. Element analyses were performed with SEM-EDS10-12,28The EC grains are characterized in the first hand by high Crwt%, FeO concentrations in the range of ~25-30 wt%, low Al at ~5-8 wt%, and MgO concentrations of ~1.5-4 wt%. The most discriminative feature, however, is , ~2.0-3.5 wt%, concentrations. For a grain to be classified as an EC grain, it ranges for all elements listedFor Os analyses whole-rock limestone samples were ground in an agate mortar. Between 3-10 gram of powdered sediment was weighted, mixed with an isotopically enriched spike containing Os, dried at room temperature over night and then mixed After fusing the mixture for 90 minutes at ssolved in 6.2 M HCl and the r

12 esidue filtered at 0.45 µm. Insoluble P
esidue filtered at 0.45 µm. Insoluble PGE-containing particles were dissolved in concentrated in a tightly closed Teflon vial at ~100° chilled in ice water to minimize the escape of volatile OsO. Osmium was then extracted from this vial with the sparging methoddirectly into the torch of a single-collector ICPMS (Finnigan Element). Typical Os blanks are 188Os is between 0.5% and a few percent. The details of the method and an evaluation References 1. Sepkoski Jr., J. J. A factor analytic description of the Phanerozoic marine fossil 2. Webby, B. D., Paris, F., Droser, M. L. & Percival, I. G. Eds., (Columbia University Press, New York, 2004). ting an agenda for marine life. 4. Heymann, D. On the origin of hypersth E. R. D. Catastrophic fragmentation of asteroids: evidence from meteorites. ssberger, E. K. Shocked meevidence for multiple impacts. Meteorit. Planet. Sci. 7. Schmitz, B., Tassinari, M. & Peucker-Ehrenmeteorites in the early Ordovician

13 . et al.mid-Ordovician fossil meteorites
. et al.mid-Ordovician fossil meteorites from Sweden. Meteorit. Planet. Sci. 9. Greenwood, R. C., Schmitz, B., Bridges, Disruption of the L chondrite parent body. New oxygen isotope evidence from Ordovician relict chromite grains. 10. Schmitz, B., Häggström, T. & Tassinari, M. Sediment-dispersed extraterrestrial chromite traces a major asteroid disruption event. 11. Schmitz, B. & Häggström, T. Extraterrestrial chromite inmarine limestone at Kinnekulle, southern Sweden - Traces of a major asteroid breakup 12. Häggström, T. & Schmitz, B. Distribution of extraterrestrial chromite in Middle Ordovician Komstad Limestone in th13. Heck, P. R., Schmitz, B., Baur, H., Halliday, A. N. & Wieler, R. Fast delivery of meteorites to Earth after a major asteroid collision. meteorite shower by multiple isochron Meteorit. Planet. Sci. environments. (Eds. Cooper, J. D., Droser, M. L. ety for Sedimentary Geology, Book 77, 17. Hammer, Ø. Biodiversity curves f

14 or the Ordovician of Baltoscandia. 18.
or the Ordovician of Baltoscandia. 18. Sweet, W. C. 19. Peterson, K. J. Macroevolutionary interppredators. The role of marine microphytoplankton in the Ordovician Biodiversification Event. 21. Cronholm, A. & Schmitz, B. Extraterrestrial chromite in latest Maastrichtian and Paleocene pelagic limestone at Gubbio, Meteorit. Planet. Sci. 22. Peucker-Ehrenbrink, B. & Ravizza, G. The marine osmium isotope record. Terra 23. Rasmussen, C. M. Ø., Hansen, J. & Harper, D. A. T. Baltica: A mid Ordovician Hist. Biol.24. Zappalà, V., Cellino, A., Gladman, B. J., Manley, S. & Migliorini, F. Asteroid showers on Earth after family breakup events. W.F., Gladman, B. & Häggström T. Express delivery of fossil meteorites from the inner asteroid belt to Sweden. 26. Alvarez, L. W., Alvarez, W., Asaro, F. & the Cretaceous-Tertiary extinction. Science 28. Alwmark, C. & Schmitz, B. Extraterrestrial chromite in the resurge deposits of the early Late Ordovician Lockne c

15 rater, central Sweden. Earth Planet. Sci
rater, central Sweden. Earth Planet. Sci. Lett. evolution of key conodont genera. Thesis, Univ. Stockholm (1998). 30. Bottke W. F., Vokrouhlicky, D. & Nesvorn31. Peucker-Ehrenbrink, B., Bach, W., Hart, S.R., Blusztajn, J. S. & Abbruzzese, T. Rhenium-osmium isotope systematics and platinum group element concentrations in oceanic crust from DSDP/ODP Sites 504 and 417/418. Correspondence and requests for matempeting financial interests.Acknowledgements This study was supported by funds to B.S. from the National D.A.T.H. from the Carlsberg Foundation. Figure 1. Global biodiversity change at family level through the early PaleozoicAlthough this diagram from Sepkoski (1995)Figure 2. Distribution of extraterrestrial (chondritic) chromite and osmium isotopes through Middle Ordovician sections in Sweden and China. 350 km apart in southern Sweden, and the Puxi River and Fenxiang sections, 4 km apart in south-central China.yielding abundant fossil meteorite

16 s intaxonomic concepts for the different
s intaxonomic concepts for the different sections. Figure 3. Total diversity of brachiopod species (number of species) through part of the Lower and Middle Ordovician in Baltoscandia.by-bed collections at eight localities. Note the dramatic increase in biodiversity (black line) and high extinction (blue line) and origination (red line) levels following e same level where extraterrestrial chromite appears and Os isotopes change in Fig. 2. CambrianOrdovicianSilurian PeriodGlobalBritish Trem.Lland.We.Lud. ArenigLlanvirn 1000500Number of genera1500 Modern fauna Paleozoic fauna Cambrian fauna Trem. F. NGS-2007-07-00117-T Volkhov Y. crassusP. originalis -8-6-4-202468 01234 68 01234 5 6 12 EC grains/kg rockEC grains/kg rockEC grains/kg rock187188Os/Os Dark grayLimestone 10 101214161868 0.8 0.4 ( ) Meteorites NGS-2007-07-00117-T VolkhovKundaP.var.Yangtzeplacogn. Global seriesand stagesDapingianDarriwilianFloian Ma MiddleLower 47246840Diversity NGS-2007-0