The snowball and slushball Earth hypothesis and the initiati

Snowball

-The earth went through a series of cooling periods or glaciogenic sequences within the cryogenian.

- Multiple hypothesis by numerous geologist have tried to explain the events that occurred during this time.

-It is debated whether the earth was completely frozen(snowball) or if patched of open water existed along the equater. (Slushball Earth)

In 1992 Joseph Kirschvink published a paper titled “The Late Proterozoic Low-Latitude Global Glaciation: the Snowball Earth”

- He desired an explanation for the widespread distribution of late neoproterozoic glacial deposit. ( Kirschvink,1992)

How?

- Weakened green house effect

- “placing more continents in the tropics would also increase the silicate weathering rate”.( P. Hoffman and D. Schrag, 2002)

-Severe weathering of continental rock of Rodinia.

- CO2 is absorbed from the atmosphere creating a sink.

-Weaker sun, since the sun gets stronger with time. Possible changes in obliquity?

- At some point the albedo effect takes over.

- Freezing from Polar Regions towards the equator

-predicts -45 0C at the equator, -70 0C at the poles and up to 700m thick ice over top of the ocean.( R. Kerr,2002)

2) Cap Carbonates

-Cap carbonates are massive layers of dolostone or limestone signifying a change in global conditions. (P. Hoffman and D. Schrag, 2002)

-Cap-carbonate sequence contain unique sedimentary structures and are depleted in C13 relative to other carbonate rocks from the neoproterozioc. (P. Hoffman and D. Schrag, 2002)

-“Around the world, Neoproterozioc glacial deposits are capped by tens or even hundreds of meters of carbonate rock”( R. Kerr, 2002)

_-Very rapid temperature change from cold glacial waters to warm CO2 waters. (P. Hoffman and D. Schrag, 2002)

3) BIF’s

-Banded Iron formations(1.85 BY).

-Layer of ice prevents the interaction of atmospheric and oceanic oxygen. (P. Hoffman and D. Schrag, 2002)

-Oceans become anoxic.

- Mid ocean ridges cause the oceans to become iron rich. (R. Kerr, 2002)

- At the end of the glacial period circulation reoccurs.(R. Kerr, 2002)

-Upwelling causes the iron to oxidize.(R. Kerr, 2002)

-Occurs only during specific anoxic times

Possible evidence of metazoan life and a complex food chain at 1.9 Gyr (Robbins et al.)

Microfossils resembling fecal pellets found in thin sections of Early Proterozoic shale.

Metazoan Life

There is controversy about the timing of the initiation of Metazoan life. It is well documented by the Ediacaran fauna and of course the Cambrian, but before this there is a lack of preservation due to the nature of soft bodied organisms and their probable low abundance if they did exist. (Benton and Harper, 2009)

So, it is a possibility that there were primitive Metazoan life forms existing before this but the preservation was prevented due to glaciation, and soft bodies

The glaciers erode as they progress and recede and would likely destroy any preserved specimens that may have existed.

Difficulties with this topic.

-Early, simpler forms of life, are much more rarely seen in the fossil record

-Much of the evidence of early marine life has been erased due to tectonic activity.

-The rocks are subjected to a lot of changes between time of deposition and present which can destroy any evidence or preservation that existed

-Lots of contradicting evidence and theories due to low amounts of data available

Contributing Factors to Metazoan Survival

-Large scale oxidation event allowed life to thrive

-When Rodinia broke up it created much more continental shelf area, which in turn gave a wider range of habitats for the metazoans to establish.

-The splitting of the continents also spread out existing lifeforms allowing for diversity

-Competition biota reduced greatly in numbers, gave metazoans a chance

Ediacaran

635-541Ma

-In the Ediacaran there are the first sure traces we have seen of Metazoan life observed as the Ediacaran fauna.

-Although the Ediacaran fauna were well documented, there is still a low amount of specimens due to unfavorable preservation, so knowledge is still limited.

-The soft bodied organisms tend to decompose and show no trace in the fossil record due to a lack of hard parts.

Any Easy Questions?

Initiation of Metazoan Life

Metazoan- A multicellular organism with complex structures andspecialized cells, animals

The snowball and slushball Earth hypothesis and the initiation of Metazoan life.

It is suggested that the mass reduction of life through the Cryogenian allowed other life forms to establish themselves without being suppressed by the pre-existing dominant biota. Life forms such as the Metazoans. (Kirschivink, 1992)

Paleoproterozoic World

Life Through Glaciations

Much of life at this point were simple organisms that relied on the sun for photosynthesis and existed in the oceans.

Life survived through the glaciations in certain areas, although much of it was wiped out due to the inhospitable environment.

The thick ice sheets blocked the sunlight making photosynthesis difficult depending on the snowball model used.

~2500 - 1600 Ma

In the hard snowball model it is much less likely that photosynthetic life could survive unless it was in melt pockets on the ice sheets due to the inability of light to penetrate.

In the slushball model life could survive in and around volcanic fields and in pockets of warmer water, where the thick ice sheets were not as prevalent.

At hydrothermal vents it is very possible for life to exist.

Cryogenian World (~835 to 635 MA)

Evidence

1.) C12/C13

- plant matter is stored in sediment.

- Greater amounts of C12 indicates how poorly the plant life was during the Cryogenian. ( P. Hoffman and D. Schrag, 2002)

-Plants prefer using lighter carbon for photosynthesis

- Volcanoes and sea floor vents spew C02 that is rich in C12. (P. Hoffman and D. Schrag, 2002)

- C12 enrichment in cap carbonates fround in nimibia from the neoproterozoic. (P. Hoffman and D. Schrag, 2002)

-Shift of c12 and c13.

-C13 increased after the glacial period indicating an increase in photosynthetic plant life. (P. Hoffman and D. Schrag, 2002)

How did the glacial period end?

- The release of CO2 from volcanic activity caused from the movement of plates.( R. Kerr, 2002)

-Layer of ice prevents CO2 cycle from fully functioning and therefore trapping C02 within the atmosphere.

- Green house effect would increase through time and cause global warming.

- It is estimated that an atmosphere with around 350 times the amount of CO2 would be needed to repel the strength of the albedo. (R. Kerr, 2022)

-This would be accompanied by an average global temperature of +50 0C and acid rain. ( R. Kerr, 2002)

Cap carbonates. Digital image. Snowball Earth. N.p., n.d. Web. 26 Nov. 2015. <http://www.snowballearth.org/slides/Ch4-38.gif>.

Alternate hypothesis: Slushball Earth and Jurmagand

Gross, G. Ice Rafted dropstone in BIF, Sayunei Fm, Rapitan Gp, NT, Canada. Digital image. Snowball Earth. N.p., n.d. Web. 26 Nov. 2015.

P.Hoffman, D. Schrag, 2002, The Snowball Earth Hypothesis: Testing the Limits of Global

Change. Terra Nova, Vol 14, No.3, 129-155.

-Proposed by geologist Richard Cowan (R. Cowan, 2000)

The earth was not “completely” frozen but left areas that that were thinly iced or open either close or along the equator. (R. Cowan, 2000)

- This a less drastic model where the low latitude temperatures are above the freezing point and the poles are warmer then -50 C (R. Cowan, 2000)

- Hydrologic cycle is allowed to continue and snow could accumulate to form globalized glaciers. ( R. Kerr, 2002)

- Photosynthetic eukaryotes and other organisms could continue to live through open patch of water. ( R. Kerr, 2002)

-Surface waters would not be completely anoxic. (R. Cowan, 2000)

Competing Hypothesis

2 proposed models to explain what the cryogenian glaciations:

1) Hard snowball

2) Slushball / Jormungand

Tectonics

Mezoproterozoic World

References

Presenters: Ryan Woodley, Stu Wells, Trey Larue

~1600 - 1000 Ma

Balgord, E., Yonkee, W., Link, P., & Fanning, C. (2013). Stratigraphic, geochronological, and geochemical

record of the Cryogenian Perry Canyon Formation, northern Utah: Implications for Rodinia rifting and

snowball Earth glaciation. Geological Society of America Bulletin, 125(9-10), 1442-1467. doi:10.1130/

B30860.1

Hoffman, P., Kaufman, A., Halverson, G., & Schrag, D. (1998). A Neoproterozoic Snowball

Earth. Science, 281(5381), 1342-1346. doi:10.1126/science.281.5381.1342

Huronian Glaciations (Young, 2013)

Why didnt life diversify after that?

Meteorite (Young, 2013)

Evidence of Metazoan life... pellet microfossils at 1.9Ga

(Robbins et al., 1985)

Fin.

Micheels, A., & Montenari, M. (2007). A snowball Earth versus a slushball Earth: Results from Neoproterozoic climate modeling sensitivity experiments. Geosphere, 4(2), 401-410. doi:10.1130/GES00098.1

Neoproterozoic

J. Kirschivink, 1992, Late Proterozoic Low-Latitude Global Glaciation: the Snowball Earth

Cambridge University Press, 51-52

Robbins, E., Porter, K., & Haberyan, K. (1985). Pellet microfossils:

Possible evidence for metazoan life in Early Proterozoic time.

Proceedings of the National Academy of Sciences, 82(17),

5809-5813.

~1000 - 542 Ma

Rodinia came together 1.3-1 Ga

Supercontinent unfavourable for diversity

Young, G. (2013). Precambrian supercontinents, glaciations,

atmospheric oxygenation, metazoan evolution and an impact that

may have changed the second half of Earth history. Geoscience

Frontiers, 4(3), 247-261. doi:10.1016/j.gsf.2012.07.003

Benton, M. and Harper, D. (2008). Introduction to Paleobiology and the Fossil Record. Blackwell Publishing., Oxford. p.235

Breakup of Rodinia

CO2 draw down

Oxidation

Ediacaran Fauna

(Young, 2013)

Cryogenian

In the Neoproterozoic era, there were periods of extensive snowball Earth glaciations that led to the establishment of the boundaries of the Cryogenian period. The Cryogenian was 850- 635 million years ago and consisted of two major periods of glaciation called the Sturtian glaciation and the Marinoan glaciation.

(Young, 2013)