Harper David A. T.

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David A. T.

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  • Preprint
    Asteroid breakup linked to the Great Ordovician Biodiversification Event
    ( 2007-09-26) Schmitz, Birger ; Harper, David A. T. ; Peucker-Ehrenbrink, Bernhard ; Stouge, Svend ; Alwmark, Carl ; Cronholm, Anders ; Bergstrom, Stig M. ; Tassinari, Mario ; Xiaofeng, Wang
    The rise and diversification of shelled invertebrate life in the early Phanerozoic took place in two major steps. During the Cambrian Explosion at ca. 540 Ma a large number of new phyla appeared over a short time interval. Biodiversity at the family, genus and species level, however, remained low until the Great Ordovician Biodiversification Event (GOBE) in the mid-Ordovician. This event represents 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 because of a lack of detailed data relating faunal to environmental change. Here we show that the onset of the major phase of the GOBE coincides at ca. 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 years. The precise coincidence between an event in space and on Earth is established by bed-by-bed records of extraterrestrial chromite, osmium isotopes and invertebrate fossils in mid- Ordovician strata in Baltoscandia and China. We argue that frequent impacts on Earth of kilometer-sized asteroids accelerated the biodiversification. This is supported also by abundant mid-Ordovician fossil meteorites and impact craters.
  • Article
    An extraterrestrial trigger for the mid-ordovician ice age: Dust from the breakup of the L-chondrite parent body
    (American Association for the Advancement of Science:, 2019-09-18) Schmitz, Birger ; Farley, Kenneth A. ; Goderis, Steven ; Heck, Philipp R. ; Bergstrom, Stig M. ; Boschi, Samuele ; Claeys, Philippe ; Debaille, Vinciane ; Dronov, Andrei ; van Ginneke, Matthias ; Harper, David A. T. ; Iqbal, Faisal ; Friberg, Johan ; Liao, Shiyong ; Martin, Ellinor ; Meier, Matthias M. M. ; Peucker-Ehrenbrink, Bernhard ; Soens, Bastien ; Wieler, Rainer ; Terfelt, Fredrik
    The breakup of the L-chondrite parent body in the asteroid belt 466 million years (Ma) ago still delivers almost a third of all meteorites falling on Earth. Our new extraterrestrial chromite and 3He data for Ordovician sediments show that the breakup took place just at the onset of a major, eustatic sea level fall previously attributed to an Ordovician ice age. Shortly after the breakup, the flux to Earth of the most fine-grained, extraterrestrial material increased by three to four orders of magnitude. In the present stratosphere, extraterrestrial dust represents 1% of all the dust and has no climatic significance. Extraordinary amounts of dust in the entire inner solar system during >2 Ma following the L-chondrite breakup cooled Earth and triggered Ordovician icehouse conditions, sea level fall, and major faunal turnovers related to the Great Ordovician Biodiversification Event.