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Does the solar orbit about the Galaxy influence terrestrial biodiversity? Coryn Bailer-Jones, Fabo Feng Max Planck Institute for Astronomy, Heidelberg EANA12, Stockholm, October 2012 Variation of biodiversity over the Phanerozoic A08 Alroy (2008) extinction rate Extinction Rate 1.0 1.5 Extinction Rate 0.10 0.15 0.5 0.0 0.00 0.05 Rohde & Muller (2005) extinction rate 2.0 0.20 RM 0 100 200 300 400 500 Time Before Present/Myr 100 200 300 400 Time before present/Myr B5 K−Pg ! 500 B18 Tr−J P−Tr Late D O−S ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! Bambach (2006) 18 mass extinctions “Big five” mass extinctions 0 100 200 300 400 500 Time before present/Myr 0 100 200 300 400 500 Time before present/Myr Coryn Bailer-Jones, MPIA from space geodesy. uth America Euler vector. Figure 1a shows a plot of diversity against time for all 36,380 genera in Sepkoski’s Compendium. In Fig. 1b we show the 17,797 genera that remain when we remove those with uncertain ages (given only at epoch or period level), and those with only a single occurrence. The smooth trend curve through the data is the thirdorder polynomial that minimizes the variance of the difference Claims of periodicity in the geological record e geomagnetic reversal time 2194 (1994). om the Global Positioning e research. Eos 85, 180 one. J. Geophys. Res. 96, ion north and south of the des. Geochem. Geophys. • • on and Andean Convergence 323–349 (Mem. Geol. Soc. ernational Terrestrial doi:10.1029.2001JB000561 m/nature. Number of genera te altimetry and ship depth ; R. Zimmerman, nd crew of the R/V Roger nd GPS stations and the support at sea. This work US National Science ...but many make unreasonable assumptions or use poor statistical methodology (CBJ Int. J. Ast. 2009) competing financial Example C. ([email protected]). • biodiversity in fossil record (Rohde & Muller 2005) • significant period of 62 ± 3 Myr claimed ................ University of ............................................ ears to fluctuate uring which hard 42 million years dium1 of the first marine genera, a cularly evident in ions enumerated many claims... 0 Age / Myr 550 Figure 1 Genus diversity. a, The green plot shows the number of known marine animal genera versus time from Sepkoski’s compendium1, converted to the 2004 Geologic Time Scale5. b, The black plot shows the same data, with single occurrence and poorly dated genera removed. The trend line (blue) is a third-order polynomial fitted to the data. c, As b, with the trend subtracted and a 62-Myr sine wave superimposed. d, The detrended data after subtraction of the 62-Myr cycle and with a 140-Myr sine wave superimposed. Coryn Bailer-Jones, MPIA Suggested astronomical mechanisms Nearby supernovae gamma rays biological extinction Perturbations of Oort cloud by Galactic tide and/or passing stars comet impacts (CBJ MNRAS 2011) Star forming regions cosmic rays cloud formation (questionable) Coryn Bailer-Jones, MPIA Suggested causes of periodicity • 846 GIES & HE motion of the Sun in the Galaxy ‣ vertical oscillation through disk (periods of 50-75 Myr) ‣ spiral arm crossing (timescale of 50-100 Myr) Fig. 3.—Depiction of the Sun’s motion relative to the spiral arm pattern, in the same format as Fig. 2 but for a smaller spiral pattern speed (!p ¼ 14:4 km s"1 kpc"1). Gies & Helsel (2005) Diamonds along the Sun’s track indicate its placement at intervals of 100 Myr. We see that for this assumed pattern speed, the Sun has passed through only two arms over the last 500 Myr. However, if we assume a lower but still acceptable pattern speed of !p ¼ 14:4 km s"1 kpc"1 (shown in Fig. 3 for !# " !p ¼ 11:9 km s"1 kpc"1), then the Sun has crossed four spiral arms in the past 500 Myr and has nearly completed a full rotation ahead of the spiral pattern. Thus, the choice of the spiral pattern speed dramatically influences any conclusions about the number and picture credit: Medvedev timing of the Sun’s passages through the spiral arms over this time interval. Coryn Bailer-Jones, MPIA The duration of a coherent spiral pattern is an open question, Modelling approach astronomical observations analytic models: periodic, trend, noise, stochastic, etc. observed geological time series predicted geological time series mechanisms: supernovae, impacts, cosmic rays, etc. Bayesian model assessment parametrized model Galaxy model solar orbit and solar environment Results: evidence for model Numerical integration of solar orbit in the Galaxy Motion in Galactic plane • • Motion perpendicular to Galactic plane Time variation of local stellar density calculate orbit for many different initial conditions of model calculate likelihood of each orbit using paleontological data ‣ average likelihoods evidence for model Coryn Bailer-Jones, MPIA Results of model comparison on paleontological data Model −1.5 −1.0 −0.5 0.0 log10(Evidence) Data: 18 mass extinctions orbital orbital periodic periodic quasi−periodic quasi−periodic random events random events nonlinear trend nonlinear trend −1.5 −1.0 −0.5 0.0 log10(Evidence) Data: “big 5” mass extinctions evidence with respect to that from a uniform model Coryn Bailer-Jones, MPIA no. genera (- cubic fit) ï ï 0 400 Modelling Rohde & Muller genera time series periodic model with additional fitted Gaussian noise black = data red = model fit 450 350 250 time BP / Myr 150 50 0 400 stochastic process (OU process) ï average likelihood is much higher for this model ï no. genera (- cubic fit) 550 550 450 350 250 time BP / Myr 150 50 Coryn Bailer-Jones, MPIA Summary, and conclusions so far • many claims that the Sun’s orbit influences the terrestrial biosphere are based on poor assumptions / statistics ‣ e.g. Rohde & Muller (2005) data are better explained by a stochastic model than a periodic one • neither solar orbital model nor analytic models (e.g. periodic, quasi-periodic) seem to explain the overall extinction rate in the past 550 Myr better than simple random models (work ongoing) • more information and references: www.astroimpacts.org Coryn Bailer-Jones, Max Planck Institute for Astronomy, Heidelberg