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!
If anyone is curious, or want to interpret the results section of this week's paper with a bit more clarity, I found the following link with detailed explanations of the types of magnetism found in rocks:
ReplyDeletehttp://magician.ucsd.edu/essentials/WebBookch7.html#WebBookse41.html
Use your own discretion with respect to the accuracy of the information though...
Great! Thank you, Adam!
DeleteFrom the same folks who brought you that lovely website, I would also add this one explaining paleomagnetic sampling:
Deletehttp://magician.ucsd.edu/essentials/WebBookse56.html
Hopefully it will help with understanding their methodology.
J. Patterson
ReplyDeleteStratigraphic evidence is often very strong in biology, anthropology and planetary evolution. To me it seemed like the paper this week addressed the broad question of what evidence there was of a global extinction event at the Permian-Triassic boundary caused by dramatic climate change by examining paleomagnetic records, isotopic analysis and stratigraphic evidence for combined terrestrial and oceanic extinction.The authors concluded that there was probably not enough evidence to support a global event at a single time period (represented by a stratigraphic layer). They found that the terrestrial extinction was at a much later time period than the oceanic extinction. The results were location specific, so the authors mentioned that their results may in fact have conveyed only a localized or anomalous effect despite use of top notch statistical methods and careful evidence collection and processing. Whatever caused the two extinctions was probably climate and atmosphere related and may have had something to do with life in the oceans. This may have been something as simple as a critical mass of oxygen in the atmosphere being reached and global repercussions of this playing out. It was a very interesting hypothesis and it will be interesting to see what new research tells us about these events.
See you on Thursday,
J. Patterson
The main thing I liked about this article is how processes of the scientists seemed to layer like the strata that they were studying. Some of the processes were a bit hard to interpret for me, but all in all the overall concepts are clear. I thought they had a logical and exact idea going into this experiement, and though their results did not truly support their intended hypothesis; they have eliminated two theorized causes of these extinctions. This accomplishment is, in my opinion, worth a lot. Lastly they have left enough of a foundation to further prove the unanswered questions in the article. I look forward to seeing if the questions asked will soon be answered, for it seems they are close.
ReplyDeleteI found this article a little difficult at first but the scientist's intentions are clear. I thought they provided enough evidence to be convincing and the fact they ruled out two possible causes of extinctions is part of the battle. There is definitely room for more research.
ReplyDeleteThis is Rebecca Camden the blog is acting funny for me.
DeleteI would also say that I found this article to be a bit hard to read at first even with being an EPS major. I think this article proves that we are still learning how to understand the geologic past and reconstructing what we believe could have happened. With them ruling out two possible causes of extinction I felt like the authors were trying to convey that these extinctions would have occurred over time rather then in one single swoop. To me this would make sense because the authors talk about localized regions that would be affected. Therefore, we can infer that the terrestrial and marine extinctions could have very likely been gradual.
ReplyDeleteI'm going to lose my mind over this paper....
ReplyDeleteIt says "[The EPP] is the horizon that is taken as a lithological expression of the last appearance datum of dicynodon" The end of the dicynodon is supposed to be the mark of the PTB as said on the first page: "At present the PTB is taken at the last appearance datum of vertebrate fossils of the Dicynodon assemblage zone." However, in Figure 5 the line for Dicynodon fossils goes well past the EPP, up to the Ward Event Bed, and that is where the terrestrial extinction is marked. This mark is in the normal polarity, while the EPP is in reversed polarity
I understand that the main point is that the terrestrial extinction occurred in normal polarity and the marine extinction occurred in reverse polarity so they must be diachronous, but it seems like the data for where exactly to place the terrestrial extinction is contradictory... or did I miss something?
Don't drive yourself crazy missing the forest for the trees here. There is definitely some confusion there, but it may well be that the terrestrial extinction doesn't have a precise scientific date established. In that case they may have posted a selection of dates for it that are provided by the specific method of analysis they are discussing.
DeleteOr maybe they just made an editing error while compiling the research from multiple scientists.
I am interested in comparing the classes alternative hypotheses from this article. I bet as a class we came up with at least seven different hypotheses. This article made me wonder if it would even be possible for major life on land to be stable without marine life and vice versa? I would guess that over a certain number of years if marine life was eliminated that life on land would then suffer mass extinction events. Due to the fact of how related all the processes on Earth are.
ReplyDeleteOverall, I felt the article was well written and I learned a lot from it. However, as with the first article we wrote a qualmri about the table, figures were very hard for me to digest.
Mike J
I found this paper easier to read than the last and the science was easier for me to comprehend. It took me a while to figure out what all of the abbreviations meant and defiantly. I agree with Mike, it made me wonder whether terrestrial life and marine life were truly independent or not. I am sure that i do not know enough ecology or biology to answer that question, but it is certainly interesting to ponder.
ReplyDeleteThe first read through on this paper was pretty difficult to understand, but having to complete the QUALMRI assignment motivated me to go through it a few more times than I otherwise might.
ReplyDeleteThe main thing that helped me was reading the conclusions first on my second read through, once you understand the information they drew out of the research it becomes a lot easier to understand which specific parts of the results are necessary to understand the conclusions.
I kind of surprised myself by understanding this paper pretty well this week.