talk

							  Did a gamma-ray burst
initiate the late Ordovician
      mass extinction?
                             Adrian L. Melott1,
 B.S. Lieberman2, C.M. Laird1, L.D. Martin3, M.V. Medvedev1, B.C. Thomas1,

  J.K. Cannizzo4, N. Gehrels4, C.H. Jackman5, R.S. Stolarski5, & D.P. Hogan1


1.Department of Physics and Astronomy, University of Kansas
2.Departments of Geology and Ecology and Evolutionary Biology, University of Kansas
3.Museum of Natural History, University of Kansas
4.Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center
5.Laboratory for Atmospheres, NASA Goddard Space Flight Center                        1
                      Mass Extinctions
  rise of mammals
• Cretaceous (About 65 Mya; TV
  coverage)
  first birds
• Triassic (About 208 Mya.)
  first dinosaurs; first mammals
• Permian (About 245 Mya; the
  worst mass extinction)
  first reptiles
• Devonian (About 360 Mya.)
  first amphibians
  Ordovician (About 440 Mya)
  first fish; first life on land         2
Vela Satellite




                 3
GAMMA-RAY SKY




                4
Isotropy of BATSE GRBs




                         5
       Gamma Ray Bursts
Distances:
Cosmological (Gpc ~ 1025-26 m)

Power:
~ 5 x 1044 W (comparable to rest of Universe)

Duration:
~ 10 seconds (+ afterglow)

Photon Energy:
    power laws with peak at
~ 100's keV—few Mev

Beamed? Describe using Isotropic Approximation—terrestrial
effects depend on incident flux                              6
  Beamed or Isotropic

M87 Jet


          Cassiopeia
          A (about
          350y)




                        7
Supernova – GRB Impact
     Comparison
Object     Power       #/gal/y    <power*P>
SN (total) 1036 W      3x10-2      3x1034
SN (L)     1034 W      3x10-2        3x1030 (months)
SN(ν) 3 Gy interval for catastrophe (Collar, PRL 76, 999 rescaled)
GRB (L)     5x1044 W 3x10-8           >1037 (burst)

Scaling from the evolution of the star formation rate, a GRB @
2 kpc is a conservative estimate of the most probable nearest
event to the Earth in the last 1 Gy. Primary uncertainty recent
GRB rate—pushing uncertainties the other way: 3 times closer

Rapid (10s) deposition: I ~ 100 to 1 MJ/m2 in X and γ rays

Results given later based on the lower fluence above
                                                                     8
Biological Effects of
 Gamma Radiation




                        9
             Atmospheric
          Radiative Transport
Opaque to gamma (100 m mean free path at STP)
Energy deposition: 99+% into chemistry
         --> N2 , O2
But, ~ 2x10-3 reaches ground* as damaging UV (2900 -3200 Å)
Our 2 kpc GRB: 20 W/m2 in “dangerous” UVB

              “Don't go out without your sunglasses!”
   Still, the bigger effects are long-term, not immediate burst
                                effects

Smith, Scalo, & Wheeler (2004) Icarus 171, 229 (astro-ph/0308311 )
                                                               10
       Atmospheric Chemistry
Usual: N2, O2, O3, ...
Possible products N2O5, NO2, N2O4, N2O3, NO, N2O
                                             N2O – whipped cream, laughing gas
Primary effects                              NO – smog --> NO2
1. Opacity - NO2 (visble, brown)             NO2 - smog, brown, nitric acid
2. Nitric Acid Rain (fertilizer?)                  3NO2 + H2O --> 2HNO3 + NO
3. Ozone depletion (UV shield destruction)   ( N2O3 – unstable) (N2O5 – nitric
   NO + O3 --> NO2 + O2                      acid)
   NO2 + O --> NO + O2
Net:      O3 + O --> O2 + O2
          Strong ozone depletion (years) leads to solar UVB
                                increase
                  Thomas et al (astro-ph/0411284):
        The following 3 plots show results from simulating the
       atmospheric effect of a typical GRB beamed at the Earth
         from a distance of about 2 kpc, at the spring equinox
                      incident over the equator.                           11
   Ozone depletion after GRB
   irradiation of atmosphere




Pre- and post-burst O3 column densities in units of 1018/cm2   12
 UV irradiation convolved with
biological weighting function for
   DNA damage—GRB effect




DNA damage is normalized to the pre-burst annual global mean.
                                                                13
NO2 OPACITY




              14
http://www.newscientist.com/news/news.jsp?id=ns99994198




                                                          15
   Environmental UV Effects
Solar UVB, 290-320 nm --90% normally absorbed by
O3
Modest increases in UVB are often lethal-even an
increase of order 20-30% for marine organisms
UV is attenuated by water depth 10's of meters (clear),
or a few meters (w/particulates, dissolved organics)
Expect depth dependence of extinction (note: many
larvae live in plankton, even when adult forms do not)




                                                          16
      Other Effects of GRB
• NO2 – Acid Rain, comparable to anthropogenic
  acidity levels (5 months’ acid rain in upstate NY)
• Climate Cooling (opacity)—roughly 2% average
  reduction in sunlight for a few months—greater at
  the poles.
• After the extinction, nitrate fertilizer? (a few g/m2,
  comparable or greater than annual rate of nitrogen
  fixing in present biosphere; not far from lawn rate)


                                                      17
Ordovician--2nd
              Largest
   Mass Extinction




                        18
                                www.ucmp.berkeley.edu/ordovician/ordov
                                ician.html
                                Courtesy W. Berry, UC Museum of
                                Paleontology


                                 Ordovician



  Candidate
  Extinction
www.scotese.com/newpage1.htm
Courtesy C. Scotese, PALEOMAP
                                                                  19
   Predicted as GRB                     Late Ordovician Data
        Effects
                                                 Yes (correlation)
 Extinction of shallow (not deep)
        water organisms !                        Yes (correlation)
   Extinction of free-swimming
            organisms !                          Yes (correlation)
   Extinction of surface floaters
plankton/planktonic larval forms !     Productivity oscillation in biosphere
                                         possibly related to nitrate boost.
         Nitric acid rain ?            Rise of life on land after extinction.

                                                  Yes – glaciation
                                                   needed “kick”
  Reduction of solar radiation –
           cooling ?                   Extinctions preceeded glaciation
  Extinctions begin with GRB !         and began with plankton

                                          Unknown (not yet observed)
No iridium layer due to asteroid, no                                      20
     244Pu residue from nearby
  supernova, but possible excess
         CONCLUSIONS                      We have no smoking gun.
• A strong GRB irradiation of             However, this is a
  the Earth is probable during            falsifiable hypothesis.
  the time interval since O2-
  enrichment of the
  atmosphere.
• Such an event would deplete
  the ozone layer, exposing
  organisms to dangerous levels
  of solar UVB.
• At least one mass extinction     Melott et al., Int’l J. of Astrobiology 3, 55
  shows characteristics            (2004) (astro-ph/0309415)
  compatible with GRB effects.     Thomas et al., ApJL submitted (astro-
                                   ph/0411284)

                                   Research supported by NASA                21
 KU Astrobiology: http://kusmos.phsx.ku.edu/~melott/Astrobiology.htm