Download Does the solar orbit about the Galaxy influence terrestrial biodiversity?

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