Snowball

EarthRoopa KameshMatt BeversdorfKathy Groome

Theory of Snowball Earth Continents and oceans were covered in ice

approximately 600 million years ago.

Earth was in a deep freeze, chemical cycles were halted; carbon dioxide accumulated in the atmosphere causing an extreme greenhouse effect.

Believed to have triggered the explosion of life forms seen in Cambrian fossils

Snowball Earth occurred during the Neoproterozoic

Research Question

Is there a correlation between the existing isotope data and unusual deposits during the Neoproterozoic (530-630 Ma) ?

Existing Evidence

Proterozoic Biostratigraphy: Persistence and the Explosion of Life

Glacial Deposits and Carbonate Caps

Isotope Analysis

Proterozoic Biostratigraphy (Fossil Record)

Shelly Fauna – mollusks, conical fossils marking the Cambrian transition

Acritarchs – organic walled, probably plant origin

Ediacarian fossils – oldest known multicellular animal life. Soft bodied, macroscopic invertebrates. Circumglobal

Stomatolites – CaCO3 buildup of algal origin

Trace fossils – traces and burrows

Hoffman and Shrag (1998)

Geologic SequenceCap Carbonates are found on top of glacial deposits in

the rock layers.

Mulden ClasticsElandshoek Slope

Elandshoek PlatformMaieberg Cap CarbonateGhaub Glacial Deposits

Ombaatijie PlatformGruis Ramp

Rasthof Cap carbonateChuos Glacial Deposits

Ombombo Ramp (approx 760 Ma)

Namibia (Hoffman et al. 1998)

Hoffman and Schrag pointing to cap carbonate above glacial dropstones.

Stable Isotope Analysis

OXYGENHeavy Oxygen-18 is incorporated into minerals. More Oxygen 18 during low temperatures.

STRONTIUMIncreased Sr86/87 ratio due to increased weathering during glaciation.

CARBON 12/CARBON 13Plants use the lighter isotope Carbon 12 in photosynthesis. The lower relative abundance of Carbon 13 means the plants were worse off (dying). Evidence in “cap” carbonates

Jacobson and Kaufmann, 1999Knoll, 2000Knoll, 2000

Design/Methods Literature Search for related data Kaufman et al. 1993. The Vendian Record of Sr and C isotopic Variations in

Seawater: Implications for Tectonics and Paleoclimate. Earth and Planetary Science letters 120(1993) 409-430.

Kennedy et al. 1998. Two or Four Neoproterozoic Glaciations? Geology 26 (12): 1059-1063.

Data Analysis Create Timeline depicting different stages ranging from Archaen to PhanerozoicAny significant difference in isotope data over time (ANOVA for 3 different isotopes every 20 My)Correlation between isotope data at different locations (ANOVA for 3 different isotopes)Correlation between different isotope data (Spearman rank analysis)

Results

A B C D E F G H I-12

-10

-8

-6

-4

-2

0

2

Interaction Bar Chart Effect: Age Class 20my Dependent: 018 With 95% Confidence error bars.

Age Class 20my

Cell

Mea

ns o

f 018

A B C D E F G H I-6

-4

-2

0

2

4

6

8

Interaction Bar Chart Effect: Age Class 20my Dependent: C13 With Standard Deviation error bars.

Age Class 20my

Cell

Mea

ns o

f C13

Data grouped by 20 My time periods. (A=520-540 My, I=680-700 My)

Oxygen (O18)

Carbon 13

A B C D E F G H I.706

.708

.71

.712

.714

.716

.718

.72

Interaction Bar Chart Effect: Age Class 20my Dependent: 87/86 Sr With 95% Confidence error bars.

Age Class 20my

Cell

Mea

ns o

f 87/

86 S

r

Strontium (Sr86/Sr87)

Isotope P-value Age groups included

Carbon 13 .0001 A-I

Oxygen 18 .0037 A-F

Strontium 87/86 .0382 A-I

Isotope Data over Time

Isotope Data from Different Locations

Location Description Author

PG Polarisbreen Group and equivalents, Svalbard and East Greenland

Kaufmann et al., 1993

NW Nama and Witvlei groups, Namibia and South Africa

Kaufmann et al., 1993

UWS Upper Windmere Supergroup, Northwest Territories, Canada

Kaufmann et al., 1993

CF Congo Craton east of Fransfontein, Africa

Kennedy et al. 1998

CD Congo Craton Farm Durrwater 66, Africa

Kennedy et al. 1998

CD CF NW PG UWS-12

-10

-8

-6

-4

-2

0

2

Interaction Bar Chart Effect: Location Dependent: 018 With 95% Confidence error bars.

Location

Cell

Mea

ns o

f 018

CD CF NW PG UWS.706

.707

.707

.708

.708

.709

.709

.71

.71

.711

.711

Interaction Bar Chart Effect: Location Dependent: 87/86 Sr With Standard Deviation error bars.

Location

Cell

Mea

ns o

f 87/

86 S

r

Strontium (Sr86/Sr87)

Oxygen (O18)

CD CF NW PG UWS0

1

2

3

4

5

6

Interaction Bar Chart Effect: Location Dependent: C13 With Standard Deviation error bars.

Location

Cell

Mea

ns o

f C13

Carbon 13

Isotope P-value

Carbon Oxygen Strontium

.0886

.0011*

.0018*

C, O and Sr for 5 locations

*Low P-value means that they are significantly different

Correlation Between Isotope Data?

Isotope Rho P-value n= Carbon 13 and Oxygen 18 0.121 0.3213 68Oxygen 18 and Strontium 86/87 -0.251 0.0288* 77Strontium 86/87 and Carbon 13 -0.18 0.1488 68

*Low P-value means that we reject the null hypothesis that there is not a relationship between the variables (independent)

Summary of the ResultsANOVA* C, Sr, and O were significantly different over time

Indicates one or more climatic changes in conditions from the Archaen to the Phanerozoic. (Does not tell us when or how extreme)

* O and Sr were significantly different between locationsTells us that the numbers are different between sites - measurement

error or other factor? (Does not tell us if locations show same trend)

* C was not significantly different between locationsCarbon data was similar for all sites

SPEARMAN* Both C & Sr and C & O are not related

* O & Sr are related (inverse correlation)

Ma Animal Fossils Geology Carbon 13 87/86 SR ratio O18535 High (0.71098) Low (-13.4)540545 High (0)550555560565 Level (-8.8)570 Level (0.708607) Level (-7.8)575 High (6.6, 5.9)580585 Low (-4.4)590 Cap Carbonate Low (-5.5) Low (-13.5)595

600Low (0.706754 - 0.710536) High (-3.4)

605610 High (4.1)

615Metazoans and simple Acritarchs

Snowball Earth Event

Possible 2nd Glaciation

Shelly Fauna, Distinctive Trace Fossils, and simple Acritarchs

Megascopic (diverse) Acritarchs

Ediacara Fauna, and simple Acritarchs

Walter et al., 2000

How does it all fit together? (after 6 hours of stress)

Conclusion

• We conclude that it is reasonable that a global glaciation occurred around 600 My ago.

• This is supported by isotope analysis, which showed that isotopes changed over time over a large area.

• The isotopes also correspond with glacial deposits and biostratigraphic data

• What do you think?