End-cretaceous cooling and mass extinction driven by a dark cloud encounter

Abstract

a b s t r a c tWe have identified iridium in an~5 m-thick section of pelagic sediment cored in the deep sea floor at Site 886C, in addition to a distinct spike in iridium at the K-Pg boundary related to the Chicxulub asteroid impact. We distinguish the contribution of the extraterrestrial matter in the sediments from those of the terrestrial matter through a Co-Ir diagram, calling it the "extraterrestrial index" f EX . This new index reveals a broad iridium anomaly around the Chicxulub spike. Any mixtures of materials on the surface of the Earth cannot explain the broad iridium component. On the other hand, we find that an encounter of the solar system with a giant molecular cloud can aptly explain the component, especially if the molecular cloud has a size of~100 pc and the central density of over 2000 protons/cm 3 . Kataoka et al. (2013Kataoka et al. ( , 2014 pointed that an encounter with a dark cloud would drive an environmental catastrophe leading to mass extinction. Solid particles from the hypothesized dark cloud would combine with the global environment of Earth, remaining in the stratosphere for at least several months or years. With a sunshield effect estimated to be as large as −9.3 W m −2 , the dark cloud would have caused global climate cooling in the last 8 Myr of the Cretaceous period, consistent with the variations of stable isotope ratios in oxygen

Ecological niche modelling does not support climatically-driven dinosaur diversity decline before the Cretaceous/Paleogene mass extinction

“…42 ), and eventually leading to depressed Maastrichtian diversity. A prolonged episode of climatic cooling throughout the latest part of the Cretaceous (from the Cenomanian/Turonian boundary onward, 93.9–66 Ma 43 ) has also been also proposed as a major driver for declining trends in dinosaur diversity up to their final extinction at the K/Pg boundary 1,8,44 .…”

Mapping the location of terrestrial impacts and extinctions onto the spiral arm structure of the Milky Way

“…2), equivalent to 71.1 to 66.0 Ma. The geological study of Nimura et al (2016), combined with insights into the possible effects of molecular clouds (Yabushita and Allen, 1989; Kataoka et al, 2014), complements…”

“…2), equivalent to 71.1 to 66.0 Ma. The geological study of Nimura et al (2016), combined with insights into the possible effects of molecular clouds (Yabushita and Allen, 1989; Kataoka et al ., 2014), complements the galactic model presented here. The end-Permian extinction, the most severe both taxonomically and ecologically (McGhee et al ., 2013), is predicted to occur in the Crux-Centaurus arm, at an approximately equal distance from the methanol maser average as the end-Cretaceous extinction.…”

“…This includes events believed to be associated with passage through the arms, e.g. high iridium-cobalt ratios suggested as being indicative of encounters with molecular clouds (Nimura et al ., 2016), superchrons as potential markers of inter-arm passage (Wendler, 2004) and increased impact cratering (Clube and Napier, 1984). The improved accuracy of event ages (high-precision records), longer and more complete sets of environmental proxy data and increasingly detailed understanding of the structure of the Milky Way (e.g.…”

“…What are the consequences for our Solar System and life on Earth as we pass through the spiral arms of the Milky Way? The potential importance of passage through the spiral arms was noted in the late 1970s and early 1980s (Napier & Clube 1979;Clube & Napier 1984, Raup & Sepkoski 1984 and receives occasional scrutiny, especially with respect to its effect on climate and glaciation (Gies & Helsel 2005;Overholt et al 2009;Svensmark 2012;Brink 2015), the timings of extinctions (Leitch & Vasisht 1998, Gillman & Erenler 2008Filopović et al 2013) and the role of gravitational perturbation during passage through regions of dense matter (Yabushita & Allen 1989;Kataoka et al 2014;Nimura et al 2016). Other studies and critiques of periodicity in impact cratering, extinctions and climate have focussed on shorter period events potentially related to oscillations through the galactic midplane (Rampino & Stothers 1984, Yabushita 2002, Rohde and Muller 2005, Lieberman & Melott 2007, Shaviv et al 2014, Meier & Holm-Alwmark 2017.…”