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 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 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 kJ 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
http://www.newscientist.com/news/news.jsp?id=ns99994198
11
Atmospheric Chemistry
Usual: N2, O2, O3, ...
Possible products N2O5, NO2, N2O4, N2O3, NO, N2O
Primary effects
1. Opacity - NO2 (visble, brown)
2. Nitric Acid Rain (fertilizer?)
3. Ozone depletion (UV shield destruction)
NO + O3 --> NO2 + O2
NO2 + O --> NO + O2
Net:
O3 + O --> O2 + O2
N2O – whipped cream, laughing gas
NO – smog --> NO2
NO2 - smog, brown, nitric acid
3NO2 + H2O --> 2HNO3 + NO
( N2O3 – unstable) (N2O5 – 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
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)
15
16
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.
17
Nitrate Rainout
18
NO2 OPACITY
19
Variability due to latitude,
season of burst
20
nd
Ordovician--2
Largest
Mass Extinction
21
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
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
244Pu residue from nearby
supernova, but possible excess
23
CONCLUSIONS
• A strong GRB irradiation of
the Earth is probable during
the time interval since O2enrichment 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