Did a gammaray burst initiate the late Ordovician
Did a gamma-ray burst initiate the late Ordovician mass extinction? Adrian L. Melott 1, B. S. Lieberman 2, 3, B. C. Thomas 1, C. M. Laird 1, L. D. Martin 3, 4, M. V. Medvedev 1, J. K. Cannizzo 5, N. Gehrels 5, C. H. Jackman 6, R. S. Stolarski 6, D. P. Hogan 1 & L. Ejzak 1 1. Department of Physics and Astronomy, University of Kansas 2. Department of Geology and Ecology and Evolutionary Biology, University of Kansas 3. Department of Ecology and Evolutionary Biology, University of Kansas 3. Museum of Natural History & Biodiversity Research Center, University of Kansas 4. Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center 5. Laboratory for Atmospheres, NASA Goddard Space Flight Center 1
rise of mammals Mass Extinctions • 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 ke. V—few Mev Beamed? Describe using Isotropic Approximation—terrestrial effects depend on incident flux 6
Beamed or Isotropic M 87 Jet Cassiopeia A (about 350 y) 7
Supernova – GRB Impact Comparison Object Power #/gal/y <power*P> SN (total) 1036 W 3 x 10 -2 3 x 1034 SN (L) 1034 W 3 x 10 -2 3 x 1030 (months) SN(ν) 3 Gy interval for catastrophe (Collar, PRL 76, 999 rescaled) GRB (L) 5 x 1044 W 3 x 10 -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 (10 s) deposition: I ~ 100 k. J to 1 MJ/m 2 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 --> N 2 , O 2 But, ~ 2 x 10 -3 reaches ground* as damaging UV (2900 -3200 Å) Our 2 kpc GRB: 20 W/m 2 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
http: //www. newscientist. com/news. jsp? id=ns 99994198 11
Atmospheric Chemistry Usual: N 2, O 3, . . . Possible products N 2 O 5, NO 2, N 2 O 4, N 2 O 3, NO, N 2 O Primary effects 1. Opacity - NO 2 (visble, brown) 2. Nitric Acid Rain (fertilizer? ) 3. Ozone depletion (UV shield destruction) NO + O 3 --> NO 2 + O 2 NO 2 + O --> NO + O 2 Net: O 3 + O --> O 2 + O 2 N 2 O – whipped cream, laughing gas NO – smog --> NO 2 - smog, brown, nitric acid 3 NO 2 + H 2 O --> 2 HNO 3 + NO ( N 2 O 3 – unstable) (N 2 O 5 – nitric acid) Strong ozone depletion (years) leads to solar UVB increase Thomas et al (astro-ph/0411284): The following 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. 12
Ozone depletion after GRB irradiation of atmosphere 13
UV irradiation DNA damage 14 DNA damage is normalized to the pre-burst annual global mean.
Environmental UV Effects Solar UVB, 290 -320 nm --90% normally absorbed by O 3 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) 15
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Other Effects of GRB • NO 2 – Acid Rain, comparable to anthropogenic acidity levels (5 months’ acid rain in upstate NY) • Climate Cooling (opacity)—few % average reduction in sunlight for a few months—greater at the poles. • After the extinction, nitrate fertilizer: ~0. 5 g/m 2 over several years. This is close to non-anthropogenic recent rates, but much greater than the rate if terrestrial plants are excluded. 17
Nitrate Rainout 18
NO 2 OPACITY 19
Variability due to latitude, season of burst 20
nd Ordovician--2 Largest Mass Extinction 21
www. ucmp. berkeley. edu/ordovician/ordo vician. html Courtesy W. Berry, UC Museum of Paleontology Ordovician Candidate Extinction www. scotese. com/newpage 1. htm Courtesy C. Scotese, PALEOMAP 22
Predicted as GRB Effects Late Ordovician Data 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 ! Nitric acid rain ? Reduction of solar radiation – cooling ? Extinctions begin with GRB ! Productivity oscillation in biosphere possibly related to nitrate boost. Rise of life on land after extinction. Yes – glaciation needed “kick” Extinctions preceeded glaciation and began with plankton Unknown (not yet observed) No iridium layer due to asteroid, no 244 Pu residue from nearby supernova, but possible excess 23
CONCLUSIONS • A strong GRB irradiation of the Earth is probable during the time interval since O 2 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 shows characteristics compatible with GRB effects. We have no smoking gun. However, this is a falsifiable hypothesis. Melott et al. , Int’l J. of Astrobiology 3, 55 (2004) (astro-ph/0309415) Thomas et al. , Astrophysical Journal Letters, in press(astro-ph/0411284) Research supported by NASA Astrobiology program 24 KU Astrobiology: http: //kusmos. phsx. ku. edu/~melott/Astrobiology. htm
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