1

Did a gamma-ray burst initiate the late Ordovician

mass extinction?Adrian L. Melott1,

B.S. Lieberman2,3, B.C. Thomas1, C.M. Laird1, L.D. Martin3,4, M.V. Medvedev1,

J.K. Cannizzo5, N. Gehrels5, C.H. Jackman6, R.S. Stolarski6,

D.P. Hogan1 & L. Ejzak1

1.Department of Physics and Astronomy, University of Kansas2.Department of Geology and Ecology and Evolutionary Biology, University of Kansas3.Department of Ecology and Evolutionary Biology, University of Kansas3.Museum of Natural History & Biodiversity Research Center, University of Kansas4.Laboratory for High Energy Astrophysics, NASA Goddard Space Flight Center5.Laboratory for Atmospheres, NASA Goddard Space Flight Center

2

Mass Extinctionsrise 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

3

Vela Satellite

4

GAMMA-RAY SKY

5

Isotropy of BATSE GRBs

6

Gamma Ray BurstsDistances:

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

7

Beamed or Isotropic

Cassiopeia A (about 350y)

M87 Jet

8

Supernova – GRB ImpactComparison

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 kJ to 1 MJ/m2 in X and γ rays

Results given later based on the lower fluence above

9

Biological Effects of Gamma Radiation

10

AtmosphericRadiative Transport

Opaque to gamma (100 m mean free path at STP)Energy deposition: 99+% into chemistry

--> N2 , O

2

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

effectseffects

Smith, Scalo, & Wheeler (2004) Icarus 171, 229 (astro-ph/0308311 )

11

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

12

Atmospheric ChemistryUsual: N

2, O

2, O

3, ...

Possible products N2O

5, NO

2, N

2O

4, N

2O

3, NO, N

2O

Primary effects1. 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: O3 + O --> O

2 + O

2

N2O – whipped cream, laughing gas

NO – smog --> NO2

NO2 - smog, brown, nitric acid 3NO

2 + H

2O --> 2HNO

3 + NO

( N2O

3 – unstable) (N

2O

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.

13

Ozone depletion after GRB irradiation of atmosphere

14

UV irradiation DNA damage

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

15

Environmental UV EffectsSolar 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)

16

17

Other Effects of GRB• NO2 – 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/m2 over several years. This is close to non-anthropogenic recent rates, but much greater than the rate if terrestrial plants are excluded.

18

Nitrate Rainout

19

NO2 OPACITY

20

Variability due to latitude, season of burst

21

Ordovician--2nd Largest Mass Extinction

22

www.ucmp.berkeley.edu/ordovician/ordovician.html

Courtesy W. Berry, UC Museum of Paleontology

www.scotese.com/newpage1.htm

Courtesy C. Scotese, PALEOMAP

Ordovician

Candidate Extinction

23

Predicted as GRB Effects

Extinction of shallow (not deep) water organisms !

Extinction of free-swimming organisms !

Extinction of surface floaters plankton/planktonic larval forms !

Nitric acid rain ?

Reduction of solar radiation – cooling ?

Extinctions begin with GRB !

No iridium layer due to asteroid, no 244Pu residue from nearby

supernova, but possible excess nitrates

Late Ordovician Data

Yes (correlation)

Yes (correlation)

Yes (correlation)

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)

24

CONCLUSIONS• A strong GRB irradiation of

the Earth is probable during 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 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

KU Astrobiology: http://kusmos.phsx.ku.edu/~melott/Astrobiology.htm