Transcript Increasingly, geochemistry have become the lens through which

1
http://www.cbsnews.com/stories/2003/11/20/tech/main584760.shtml
2
Huge Meteor Crater Found In Antarctica
May Have Been Caused By Same Meteor That Wiped Out Most Earth Species
"There are at least 20 impact craters this
size or larger on the moon, so it is not
surprising to find one here.“
Ralph von Frese, Ohio State University
BANGKOK, June 7, 2006
(AP) A massive crater in Antarctica may have
been caused by a meteor that wiped out
more than 90 percent of the species on Earth
250 million years ago, an American geologist
said Wednesday.
The 300-mile-wide crater lies hidden more than a
mile beneath a sheet of ice and was discovered by
scientists using satellite data, Ohio State University
geologist Ralph von Frese said.
Von Frese said the satellite data suggests the crater
could date back about 250 million years to the time
of the Permian-Triassic extinction, when almost all
animal life on Earth died out, paving the way for
dinosaurs to rise to prominence.
The crater was found in what's known as the Wilkes
Land region of the East Antarctic Ice Sheet.
"This is a strong candidate for the cause of the
extinction," von Frese told The Associated Press in
a telephone interview from Ohio.
"This Wilkes Land impact is much bigger than the
impact that killed the dinosaurs, and probably would
have caused catastrophic damage at the time," he
said.
Similar claims were made in 2004 when a team led
by Luann Becker of the University of California
reported that a crater off the northwest coast of
Australia showed evidence of a large meteor impact
at the time of the early extinction.
That team relied heavily on core samples provided
by an oil company drilling in the region as evidence
for its findings.
The prevailing theory holds that the Permian-Triassic extinction was caused by a series of volcanic
eruptions over thousands of years that buried what is now Siberia in molten rock and released tons of
toxic gases into the atmosphere, changing the Earth's climate.
Von Frese — who announced his findings last month at an American Geophysical Union meeting in
Baltimore — acknowledged his discovery lacks such hard evidence. He said he wanted to visit Antarctica
to hunt for rocks at the base of the ice along the coast that could be dated.
"There is skepticism and people are asking where is the other evidence and where are the rocks," he said.
"You do want to have other evidence. The strongest evidence would be rocks from the event, including
meteorite fragments."
Von Frese's findings so far rely on data from a NASA satellite that can measure fluctuations in gravity
fields beneath the ice.
The data revealed a 200-mile-wide area where the Earth's denser mantle layer bounced up into the
planet's crust. This is what would happen in reaction to such a big impact, in the planetary equivalent of a
bump on the head, von Frese said.
When the scientists overlaid their gravity image with airborne radar images of the ground beneath the ice,
they discovered imprints of lumps and ridges from the meteor that indicated impact. Von Frese has spent
years studying similar impacts on the moon.
"There are at least 20 impact craters this size or larger on the moon, so it is not surprising to find one
here," he said. "The active geology of the Earth likely scrubbed its surface clean of many more."
The crater's size and location, von Frese said, also indicated that it could have begun the breakup of the
Gondwana supercontinent by creating a tectonic rift that pushed Australia northward.
Approximately 100 million years ago, Australia split from Gondwana and began drifting north away from
what is now Antarctica, pushed by the expansion of a rift valley into the eastern Indian Ocean, von Frese
said. The rift cuts directly through the crater, so the impact of the meteor may have helped the rift to form,
he said.
By Michael Casey
©MMVI The Associated Press. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.
http://www.cbsnews.com/stories/2006/06/07/tech/main1690300.shtml
3
How sudden was the extinction?
Stratigraphic ranges of fossil species (indicated
by vertical gray lines) from the latest Permian
to the Early Triassic in the Meishan sections,
China. Species numbers are shown on the x
axes. (from Jin et al., 2000)
Species Number
Previous Idea: Extinction was gradual over 5-10 Myr
New idea: Extinction took <500,000 years and closely coincides with a
shift in d13C.
4
How can CHRONOS help us
understand mass extinctions?


Are the extinctions synchronous worldwide?
Is the carbon isotope excursion synchronous
worldwide?
» What does it mean?

Do other geochemical proxies show global
change?
» Did temperatures change? (oxygen isotopes)
» Did the sulfur cycle change (e.g., enhanced
weathering of pyrite)? (sulfur isotope)
» Was there enhanced weathering of continental
crust? (strontium and osmium isotopes)
5
CHRONOS and Geochemical
Proxies: Natural Partners in
Climate Change and
Paleochemistry Research
June 14
Ames, Iowa
6
Outline
What are geochemical proxies?
 How do proxies work?
 Examples of proxy applications

» Oxygen isotope paleotemperatures
» Carbon isotopes and the carbon cycle

Why do geochemists need CHRONOS?
7
What are Geochemical
Proxies?
Geochemical
proxies are
geochemical
measurements that
serve as a measure
of some other
environmental
variable
8
How do proxies work?
 Paleothermometers
 Tracers
9
Abelone shell
 18O/16O
ratio in
CaCO3 (d18Ocl)
function of T and
water 18O/16O (dw)


Fossil shells lock
in T at time of
growth
Resolution ±0.5°C
Temperature (°C)
Oxygen Isotope (18O/16O) Paleothermometer
10
Seasonal Temperature Change in
Modern Mollusk Shells –
Calibrating the Method
Kobashi et al. (2001)
11
12
Oxygen isotope records of modern Conus shells
Stetson Bank (20-30 m)
Alligator Point
Kobashi and Grossman., 2003
2
Juvenile
2
Sr/Ca = 0.045*T + 0.24 (R =0.64)
-1
1.75
Sr/Ca mmol mol
Other
Paleothermometers
1.5
1.25
1
Mg/Ca in
foraminifera
 Sr/Ca in
corals,
mollusks

0.75
15
-1
3
Sr/Ca mmol mol
13
20
Adult
25
30
35
30
35
Temperature (ºC)
Sr/Ca = 0.072*T
- 0.13 (R =0.68)
2
2.5
2
1.5
1
15
20
25
Temperature (ºC)
Sr/Ca Paleotemperature relations in Conus
shell aragonite (Sosdian et al., in press)
14
Application:
Climate Change
in the Cenozoic
Into the Icehouse
15
Samples
Record based on
DSDP and ODP
cores
 Sample material:
benthic foraminifera

16
Earth’s Climate
Record for the
Last 70 Million
Years
0
4
8
12
Temperature (°C)
17
Tracers
18
Changes in
solar radiation
Ocean
Weathering
http://www.aesto.or.jp/j-desc/english/image/Figure-1.gif
19
Productivity
and
biosphere
Ocean
circulation
11B/10B
13C/12C
13C/12C
13C/12C
187Os/
7Li/6Li
18O/16O
87Sr/86Sr
13C/12C
34S/32S
15N/14N
143Nd/144Nd
188Os
13C/12C
44Ca/40Ca
34S/32S,
18O/16O
56Fe/54Fe
Ir
REEs
97Mo/95Mo
Sr/Ca
Mg/Ca
33S/32S
REEs
30Si/28Si
30Si/28Si
34S/32S
44Ca/40Ca
Alkenones
56Fe/54Fe
Pb isotopes
34S/32S
Cd/Ca
Ge/Si
H/C, O/C
Ba
87Sr/86Sr
97Mo/95Mo
Hf isotopes
187Os/188Os
143Nd/144Nd
Pb isotopes
Sr/Ca
Mg/Ca
Atmospheric
chemistry &
ocean pH
18O/16O
Salinity and
ice volume
2H/1H
Temperature
11B/10B
Weathering
and crustal
cycling
3He/4He
Extraterrestrial
Local and
Global redox
Deep Time Proxies*
Biomarkers
Fluid
inclusions
in salt
*Incomplete and becoming more
incomplete by the day.
20
d13C (‰ versus PDB)
Application of a Proxy: When did
photosynthesis become important in the
carbon cycle?
1
-6
-25
Volcanic CO2
Ocean
DIC
Sedim.
Sedimentary
carbonate carbon
Application of a Proxy: When did
photosynthesis become important in the
carbon cycle?
d13C (‰ versus PDB)
21
Ocean
DIC
1
-6
-25
Volcanic CO2
Ocean
DIC
Plant biomass
Sedim.
Sedim.
Sedim.
Sedimentary
carbonate carbon
Sedimentary
carbonate carbon
Sedimentary
organic carbon
Carbon and
Sulfur
Isotope
Records of
Earth
History
Age (billion years)
22
23
Zachos et al., 2001
Carbon isotope excursion in fossil mammal teeth and
Paleosol carbonates from Bighorn, Basin, WY
Estimated MAT (°C)
Age (Ma)
24
d13C of Paleosol Carbonate
d18O of Hematite
Koch, 1998
25
Gas Hydrates – Methane in an Ice Cage
Images from: http://www-gerg.tamu.edu/photogallery/gerg_photogallery.asp
Methane hydrate
structure
26
d13C (‰ versus PDB)
Carbon Isotopes
1
-7
-25
Sedimentary
Carbonate carbon
Whole Earth carbon
Sedimentary
organic carbon
Gas hydrates
Weath.
Sedim.
Ocean DIC
27
CHRONOS:
Why do geochemists need it?
Stable isotope data from brachiopod shells from North
America and the Russian Platform (from Mii et al., 2001)
.
28
d13C (‰)
4
5
6
7
1
350
355
360
Serpuk.
Lower Carboniferous
345
Visean
340
Tournais.
335
3
4
5
6
1996
V
.
Mosc. Kasi.
Serpuk. Bashkir.
1994
Panthalassan Paleotethyan
Visean
Mosc.
V
325
330
2
Gz.
Tournais.
320
Lower Carboniferous
Age (Ma)
315
3
Upper Carboniferous
310
Bashkir.
305
Upper Carboniferous
300
2
Kasi.
1
295
d18O (‰)
Panthalassan
Paleotethyan
7
Marine Fossils and Microfossil d18O
29
Lots of data but what do they mean?
0
N = 5226
Temperature (°C)*
12
40
73
108
170
*Temperature using O’Neil et al. (1969) assuming dw = -1‰
d18O (‰)
30
Early
Carboniferous
Late Carb.
Permian
Perm.Carb.Goldschmidt
The data are complex.
31
Count
Count
Geographic Variation in the d18O of PermoCarboniferous Brachiopods
d18O (‰)
d18O (‰)
d18O (‰)
32
Throw out
bad samples,
not bad data!
Only the best
coffee beans . . .”
33
I want it and I want it now!

Comparison with all comparable records
» Stratigraphic (default scheme)
» Scatter diagrams (e.g., d13C versus d18O; vs.
%CaCO3; vs. %organic C, etc.)
» Records from limestones with > 80% carbonate, <
0.5% Corg, < 100 ppm Mn, etc.

Variable correlation schemes and age models
» Priority to conodonts or paleomagnetics or
ammonoids or d13C or other chemostratigraphy




Regional variation
Running averages: Set window and steps
Time series analysis
Objectivity