Week 3 - Stratigraphy

Hi folks! The reading for this week is as follows:

DeKock MO, and Kirschvink JL. 2004. Paleomagnetic Constraints on the Permian-Triassic Boundary in Terrestrial Strata of the Karoo Supergroup, South Africa: Implications for Causes of the End-Permian Extinction Event. Gondwana Research 7(1):175-183.

This paper uses paleomagnetic reversals in combination with known stratigraphic data marking the Permo-Triassic boundary to compare the timing of the end-Permian extinction of terrestrial organisms to that of marine organisms.

For this week’s discussion, here are some questions you may want to think about:

1)      Do you think there methods were appropriate to examine the differences between the end-Permian extinction in marine and terrestrial environments?  Why or why not?

2)      In light of what we learned in class on Tuesday, what do the strata imply about the terrestrial environment at the Permi-Triassic boundary?

3)      If, as the authors posit, the marine and terrestrial events were diachronous, how can we test if a causal relationship exists between the two?

As always, these questions are only suggestions and you are free to bring up any other insights/questions/concerns about the article.  Have fun and see you on Tuesday!

Week 2 - Paleogeography and Paleomagnetism

This week’s discussion paper : 

Angiolini, L., Gaetani, M., Muttoni, G., Stephenson, M.H., Zanchi, A., 2007. Tethyan oceanic currents and climate gradients 300 m.y. ago. Geology, 35(12), 1071-1074. 

Angiolini et al. (2007) are using many of the principles that we discussed on Tuesday, related to paleogeography, to attempt to explain the fossil assemblages that the authors have found in Iran.  Let us know what you think of the paper.  Below are a few questions to guide your discussion. 

1. Given that the paleomagnetic discussion in Angiolini (2007) contains jargon that we may not all understand, how solid do you feel that the paleogeographic reconstruction is?  What issues might arise from this?
2. It is easy to get lost in the weeds with terminology presented in this week’s paper.  Without worrying too much about brachiopods and statistics what is the study of the fossil record trying to show in this particular study?  How convincing is the authors’ story?

As always, if there is something that totally blows you away, or leaves you more confused than you ever thought possible, feel free to post your thoughts and questions, so that we may be able to address these things in discussion on Thursday. 

Week 1 - Snowball Earth

This week, as an exciting opening to the course, we're reading about the Snowball Earth hypothesis. This hypothesis states that, at three or four time periods between 2220 million years ago (mya) and 560 mya, the earth was completely covered in ice. There are multiple lines of evidence supporting the Snowball Earth hypothesis, the most important of which is glacial deposits from this time period on all continents, even those which were located in the tropics. These deposits are often covered by carbonate rocks, called cap carbonates, that could have been formed during rapid warming events following long periods of glaciation. Ratios of C13 (a stable carbon isotope) to C12 in these rocks are consistent with a decrease in biological activity during each glaciation. There are several proposed causes of these glaciations. One of these is the breakup of the supercontinent, Rodinia, and the migration of the smaller continents into tropical regions. (Hoffman and Schrag 2000). This hypothesis is tested in our primary research paper for the week, Donnadieu et al. 2004.

The breakup of Rodinia could have caused an increase in rainfall, because smaller continents with greater shoreline could be exposed to more rainfall. Rainfall, in turn, causes weathering of CO2 from land into the ocean, leading to decreased CO2 in the atmosphere. This could eventually result in ice forming at the poles, spreading slowly toward the equator. Ice reflects sunlight from the Earth's surface back into space, which would cool the Earth further, a phenomenon known as albedo. This positive feedback loop could result in complete or near-complete glaciation of the earth. Donnadieu et al. (2004) use climate models to test the hypothesis that the breakup of Rodinia could decrease the levels of atmospheric CO2 enough to initiate this process. They find that increased weathering resulting from changes in geography could have lowered Earth's average temperature by around 8 C, a level able to trigger a full glaciation.

In your comments, and for class on Thursday, think critically about this hypothesis. Do you think evidence is sufficient to support a Snowball Earth? What evidence is there against a Snowball Earth? What are your thoughts on using a modeling approach to study this problem? How would you study this problem? How do you think life could have survived during a Snowball Earth climate? How could the climate have escaped from a Snowball Earth glaciation? Most importantly, what questions do you have about the Snowball Earth hypothesis?

Citations:

Donnadieu, Yannick, Yves Godderis, Gilles Ramstein, Anne Nedelec, & Joseph Meert. 2004. A 'snowball Earth' climate triggered by continental break-up through changes in runoff. Nature 428: 303-306.

Hoffman, Paul F. & Daniel P. Schrag. 2000. Snowball Earth. Scientific American 282: 68-75.

Week 0

This is a test post. Next week we will be reading our first scientific paper and doing an introduction to the climate system. I will post the syllabus, course schedule, and e-reserves information when I have it.