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Reflection #7:Comings and Goings of Global Glaciation......(2004)
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 Reflection #7:Comings and Goings of Global Glaciation......(2004) |
topic started 1/10/04; 11:10:29 AM
last post 4/26/05; 12:43:58 AM |
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 hamannmm@m... - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004) 
3/1/04; 8:39:31 PM (reads: 31743, responses:
0) |
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What was done/ what were the methods?
In this article, Hoffman et al. discuss the presence of the Neoproterozoic history and its relation to glaciation and global climate change. They studied the different rock formations and composition of Tropical platforms in Namibia. Presented with the data are also history and explorations of the various hypotheses that encompass the Neoproterozoic earth history.
-True Source of Data:
Isotopic shifts, including the secular variation of Carbon 13 in marine carbonates. Deposition sequences. Also presented was information gathered from the generation of thermal subsidence and sediment accumulation using lithospheric stretching factors.
Data of this article was centered on Proterozoic carbonates and the levels of Carbon 13 they contained.
What was learned/ were the results?
Isotopic shifts account for fractional organic to total carbon burial rates, biological productivity in the surface ocean, vertical circulation rate for the whole ocean, isotopic composition of carbon sources, and isotopic fractionation related to carbonate ion concentration. It was also found that "the overall negative isotopic excursion begins and ends in peritidal sediments and spans a total thickness of 500 m."
What did I get out of this article?
That a lot of hypotheses exist for the "initimate association of glacial diamicities with typical warm-water carbonates" and none of them have been accepted as correct. All but one of them has been proven incorrect, but there is little remaining data to determine if the last standing hypothesis is incorrect or not.
How did/will this article change my thinking?
I really enjoyed the introduction to this paper, especially the contrasting hypotheses and the explanations behind them. It really made the history of glacial diamictities gain a personality of their own.
Do you have any Rasthof and Maieberg cap carbonates? If so, could you bring them in for show and tell? Does the Maieberg resemble plagioclase feldspar?
Although I enjoyed some aspects of this article, I didn,t like the overall rhetoric in which it was written. It is one thing to be a little informal in presenting all the hypotheses, but the conclusion should have definitely not mentioned Sherlock Holmes; I don't know about anyone else, but I found this utterly tacky. Since the scientific procedures presented in these papers are things I have not done I'm finding myself becoming increasingly critical of the manner in which the articles are written and the tone they amplify.
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miller43@m... - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
3/4/04; 10:32:40 AM (reads: 31695, responses:
0) |
Comparison of two stratigraphic intervals located in northern Namibia which suggest glacial deposits once occuring tropical regions during the Neoproterozoic period. Carbon^13 concentration and distribution was a contributing factor in stating these glaciations occurred. An overview of contending hypotheses provided contrast to the Neoproterozoic glacial deposit notion.
Williams suggests that the axial tilt during the Neoproterozoic period exceeded 54 degrees which would have caused climactic zonation reversal and insolation reversal resulting in longer seasons, higher carbonate deposition and warmer temperatures. Another hypothesis suggest Inertial-Interchange True Polar Wander (IITPW) as the crust and mantle of Earth shifting contrary to the tilt of the Earth, going so far as moving continents up to 90 degrees in latitude in a matter of a few million years. This would causes sudden changes in climate by regional changes as well as circulation and weather alterations. Other accounts suggest solar output was 93% to 94% during the Neoproterozoic period, stating that CO2 levels could have offset the solar luminosity and provided from freezing tropical temperatures if other Earth conditions fell in place. Diamictites in the noted glacial intervals have the same clast and matrix compositions suggesting similar origins. Dating of either cap as well as comparing there qualities and also carbon-isotopic composition of carbonates elaborated on either intervals origin.
A number of contending hypotheses, although appearing to be discredited toward the end of the article to a minor degree, provided contrasting views toward how the Neoprotozoic intervals could have formed. It was learned that the two intervals appear to have qualities suggesting a similar origin.
I was interested to learn that so many theories could exist to discredit how and why two intervals within the geologic time scale existed. I learned that a wide range of hypotheses suggesting incredibly drastic alterations in climate and Earth's crust exist and are not necessaryly to far fetched in the realm of speculation that must be done in determining how and why past events occurred the way they did.
I enjoyed the volley between the contending hypotheses, how they at first discredited the viability of Brian Harland's speculation on the intervals, and then how they themselves were basically discredited on the basis of validity towards the end of the report. I became quite lost within the portion comparing and contrasting the qualities of each interval. Overall, I was left with the feeling that no matter how conservative a hypotheses may seem, it should not be taken as truth without comparing it to others, no matter how outrageous they may seem. Also, not to take what is speculated to much to heart until an ample amount of evidence suggest otherwise.
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caritymr@m... - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
3/8/04; 4:00:40 PM (reads: 31621, responses:
0) |
| The contention that the Earth's tilt could have been 54 degrees is insane. That's interesting to think about. The authors of the text say that if this were the case the Earth's climatic zonation would have been reversed. Wow. Also, the effects of the seasons would be greatly amplified, as well. Apparently, though, the data do not support this hypothesis. Lots of possible explanations are proposed, and the authors do a (seemingly) good job of shooting down many of these possibilities. I say seemingly because some of these theories and retorts are somewhat confusion because of the jargon. It seems like the authors do a good job of summarizing each of the potential explanations for glaciation models. For instance, they say that the high obliquity hypothesis does not take into account the aragonite precipitates, the hypothesis that posits that there were portions of the Earth's surface that moved faster (with plate tectonics) according to where their location was relative to the poles was shot down because there are no transitional mid-latitude facies (as predicted by the model), and lastly the theory that diamactites are just impact ejecta is contradicted by a negative isotopic shift. Finally, the ocean overturn hypothesis is nullified by the predicted time limit for the negative excursion of the Ghaub glaciation. So, essentially the final word is that none of the theories hold up, and because of this, the researchers believe that there is more research to be done in order to find a definitive answer.
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nagyrc@m... - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
3/9/04; 12:18:38 AM (reads: 31603, responses:
0) |
This article presented some hypotheses for the paleoclimatic dichotomy including orbital obliquity, true polar wander, reduced solar luminosity, snowball albedo, carbon dioxide drawdown, stagnant ocean overturn, and reinterpretation of diamicites. Carbon isotopic records were gathered from the Congo craton in Namibia. They looked for possible ways of how at one point in time the tropics could have been glaciated. They looked at "isotopic shifts due to fractional organic to total carbon burial rates, biological productivity, vertical circulation rate of the ocean, isotopic composition of carbon sources, and isotopic fractionation and carbonate ion concentration."
They found that the "carbon-isotopic composition of Phanerozoic marine carbonates is complicated by the vital effects of skeletal organisms and pervasive bioturbation. After investigating each hypothesis, they found most of the hypotheses were not supported. Further information and exploration of these and other hypotheses are needed to continue this study.
I did not get as much as I would have liked out of this article. I felt that I was more confused and lost by all the geological terms, that I did not learn that much. In general what I learned was that there were a bunch of hypotheses presented, but they were not supported by the research done for this article. Obviously further studies on this topic would be helpful in the elaboration of this experiment.
This article presented some hypotheses with drastic effects. The earth having a tilt of 54 degrees was one of them. Although I guess that this could have been possible at one time, it is hard to imagine what the conditions of the earth would have been like. The idea of a snowball earth is also somewhat hard to fathom. With the entire surface of the earth, both land and water, frozen very little would be left living if anything. I feel that perhaps with more data and support for these ideas, they would appear more plausible.
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smithdb1@m... - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
3/11/04; 1:52:19 PM (reads: 31610, responses:
0) |
Hoffman and et. al. discuss the Neoproterozoic era of glaciations and what might have caused a "snowball earth." They find evidence in the forms of carbonate deposits left by glaciers in the Congo craton in Namibia, which they propose that the tropics might have been covered by ice. They suggest that polar tilt, orbital change, reduced solar radiation, decreased carbon dioxide in the atmosphere, and increased surface albedo from a ice-covered earth could have all contributed to glaciation.
The authors found evidence to suggest that the axial tilt of the earth was more than 54 degrees, which would have caused a change in climate zonation and season lengths and also a change in global temperatures. They also suggest another hypothesis that the crust of the earth had moved relative to the polar axis, moving continents up to 90 degrees in lattitude in just a few million years. The sun's relative output in solar radiation was also 93-94% of what it is today, which would have been a large factor in a cooler global climate.
Further research is needed on the carbon isotope deposit studies as the evidence for proving glaciation in the Namibia region is unclear. There are a lot of factors to be considered when looking for geological evidence to support global glaciation. Other influences, such as bioturbation and skeleton deposits from animals could have altered geologic formation.
I still find it difficult to believe that most of the earth was covered by ice, especially along equtorial regions. However, these authors show extensive evidence through geolocial findings that ice may have covered areas of the planet that we would never consdier ice being present. I am just amazed that if the earth and oceans were covered by ice, how photosynthetic organisms or primitive life could have survived and carried on after such a large planetary glaciation..
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Gattje@m... - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
4/4/04; 7:15:37 PM (reads: 31734, responses:
0) |
In this article, Hoffman talked about the Neoproterozoic history and how it effected glaciation and global climate change. By complaring two stratigraphic intervals in Nambia, it showed that there were glacial deposits occuing in tropical regoins during the Neoproterozoic period.
The idea that the axial tilt during the Neoproterozoic period exceeded 54 degrees amazes me! this would have resulted in longer seasons, higher carbonate deposition and warmer temperatures. Another hypothesis suggests that the crust and mantle of earth shifted contrary to the tilt of the earth, moving continents up to 90 degrees in latitude within a couple million years. All of hte hypotheses presented were very interesting, but towards the end of the article a number of them were discredited because it was found that the two intervals appear to have qualities showing that they might have similar origin. All of the different hypotheses interested me, it is hard for me to believe that the earth has gone through so many drastic changes!
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panzake@m... - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
4/13/04; 9:03:54 PM (reads: 31713, responses:
0) |
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Hoffman et. al. discuss the Neoproterozoic era of glaciations. This may have caused a snowball earth. They have found evidence in Namibia that the tropics may have once been covered by ice. Some proposed contributors to glaciation include polar tilt, increased surface albedo, and reduced solar radiation.
They felt the earths tilt exceeded 54 degrees and therefore caused changes in climate zones. This in turn would cause changes in seasons and global temperatures.
It is weird to think that areas we vacation to today may have once been covered in ice. There has been so much change on the earth that it is hard to follow. This article was very interesting and I feel I took a lot from it. |
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Doug - Re: The Wide Wide World of Sports
2/25/05; 9:50:04 PM (reads: 30957, responses:
0) |
What was done:
Hoffman looked at historical climate and glacial changes. This was accimplished by looking at rock formations, polar wander, and other phenomena such as sun strength. Most (or all, I cannot tell) of the data was collected in Namibia.
What were the methods:
As the graphs illustrate, some of the main techniques usec included thermal subsidence analysis and sedimentation accumulation analysis (looking at layers in the rock). Hoffman and his group also used carbonate analysis (the same as carbon-13?!) to date some of the events used in the formation of the rocks.
What was learned:
Unfortunately Hoffman was unable to prove his hypotheses. He jokes that if he used Sherlock Holmes' deductive reasoning, that he would assume that the opposite of his (Hoffman's) hypotheses would be true. He then acknowledges that it is not this simple. One cool statistic that was learned from this article was that is took 9.2 million years to accumulate 125 meters of sediment. This is about .001 cm a year, not a fast rate.
How this article changed my way of thinking:
The main thing I gained from this article was how complicated it is to determine the Snowball Earth phenomena. Rather than just taking one test to prove its existence, it took several and they still came back rather inconclusive. It just makes you realize that even if a process seems intuative and logical, science still might not be able to support it.
Fun Fact: Ron Hextall of the Philadelphia Flyers is the alltime leader in penalty minutes for a goalie.
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Justin - Snow cone anybody?
2/28/05; 6:08:52 PM (reads: 30874, responses:
0) |
The idea that the entire globe was covered with ice during the Neoprotezoic ear is discussed. The date coming from Namibia shows that carbonate deposits can be found which were left be glaciers. This leads to the idea that the tropics could have been covered in ice, and if the tropics were covered in ice the rest of the world as well. Polar tilt, orbital change, reduced solar radiation, decreased carbon-dioxide levels, and the ice causing increased surface albido could all have caused the global glaciation.
Their are a lot of hypotheses out there. One that the Earth's tilit was in the 50s of degrees. Others say that the continents were located at higher latitudes during this time. I'm not sure where their data came from. But they did use the carbonate found in the rocks in Namibia.
Their are so many different factors that are affecting this situation that more research is needed in order to accurately prove a hypothesis on the topic.
A lot of different things need to be examined before the snowball earth theory can be proved. I hope my life goals aren't this complex.
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Adam Brule - Axial Tilting....Gone Extremly Wrong!
2/28/05; 10:21:35 PM (reads: 30859, responses:
0) |
<>What was "Done" (methods. true source of data)?
Hoffman et al. in this article
specifically looked at glaciation and the possibility of a snowball Earth
during the Neoproterozoic era. They
looked at the rock stratigraphic, rock formations in
<st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. What they discovered was remarkable, that the
tropical regions contained evidence of glacial deposits. They proposed these findings based on the
deposition sequences, specifically thermal subsidence and stretching factors,
of Carbon 13.</>
<>
What does this mean?
If the tropic region was indeed
once covered by glaciers during the Neoproterozoic era as the authors claim,
they suggest that the axial tilt of the Earth may once have exceeded 54
degrees. This would result in much
longer seasons with increased solar radiation.
There was also suggestion of plate techtonics moving the plates against
the grain of tilt making the Earth tilt 90 degrees.</>
How did/will this article change my thinking?
It was interesting to think of
all these dynamic degrees of tilt that the Earth has been throughout time. I always speculated why the Earth was on a
tilt of 23.5 degrees and why not some other tilt like other planets, and what
exactly causes tilt. Although this
specific question was not addressed, its just something that provokes me. It was also nice to see the
point/counterpoint layout, because it gave you the ability to see both sides
and make your own conjectures.
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Doug - Extreme Explanations
3/2/05; 12:24:44 AM (reads: 30867, responses:
0) |
Amy Barton
The retreat and advance of glaciers on a Neoproterozoic
Tropical platform was discussed in this article. There are several hypotheses for this
occurrence including: high orbital obliquity, true polar wander, reduced solar
luminosity, snowball albedo, CO2 drawdown, and stagnant ocean overturn. Carbon-isotopic records were obtained and
used as support for the hypothesis that glaciers existed in the tropics. A number of hypotheses were presented and discussed. For example, Williams proposed that the earth≠s
tilt was 54 degrees until the end of the Proterozoic √ which is significantly
larger than the normal 22-24 degrees.
Another hypothesis dealt with polar wander. The reasoning for this was continents moving
in or out of polar regions would experience short-term sea level rises or
falls. Many other explanations were
stated, but the article concluded with a section that pointed out flaws in all
of the hypotheses. The authors feel that
one of the contending hypotheses must be an explanation that is consistent with
the data, but it not sure which one.
One point that I found very interesting was the number of differing
explanations for the association of glacial diamictites with typical warm water
carbonates. No one single explanation
seemed to best ≥fit≈ with the data.
While this does not mean that the reason is not there, it could (and
probably does) suggest that more data needs to be collected and more research
needs to be performed on this subject.
To be honest, I have never thought of the tropics being an
area covered with ice. While there is
some evidence that seems to support this, no single explanation has been widely
accepted. Many of the possible
explanations presented in this article also seem a bit extreme, which makes me
skeptical.
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David Emerman - Re: A lot of junk after the article
3/2/05; 10:40:19 AM (reads: 30844, responses:
0) |
In this article, Hoffman discusses evidence for the theory of snowball earth. Snowball earth is the theory that at one time the whole earth was covered by a sheet of ice, including the ocean. Evidence of carbonate deposits left by glaciers was found in <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. Many causes for the evidence found are proposed including, high orbital obliquity, polar wonder, reduced solar luminosity and CO2 drawdown.
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p> </o:p>
Huffman believes that the earths tilt was greater then 54 degrees, causing longer seasons. This could be a possible explanation for the carbonate deposits found in <st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. In the end Hoffman was unable to produce any conclusive evidence. Other theories include movement of continents could produce the evidence found.
<o:p> </o:p>
I find it hard to believe the snow ball earth theory. It seems that if it were to happen once then it would be cyclic and could happen again. I am a supporter of Milankcovitch and am not sure how his theories would fit in with the snowball earth theory.
<o:p> </o:p>
I don‚t think that much more conclusive evidence will be found for the snowball earth theory. It seems that anything found will be questionable and that a multitude of possible causes will be found. It seems like a difficult subject to prove.
Add your comments here!
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David Emerman - Re: A lot of junk after the article
3/2/05; 10:40:21 AM (reads: 30824, responses:
0) |
In this article, Hoffman discusses evidence for the theory of snowball earth. Snowball earth is the theory that at one time the whole earth was covered by a sheet of ice, including the ocean. Evidence of carbonate deposits left by glaciers was found in <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. Many causes for the evidence found are proposed including, high orbital obliquity, polar wonder, reduced solar luminosity and CO2 drawdown.
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p> </o:p>
Huffman believes that the earths tilt was greater then 54 degrees, causing longer seasons. This could be a possible explanation for the carbonate deposits found in <st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. In the end Hoffman was unable to produce any conclusive evidence. Other theories include movement of continents could produce the evidence found.
<o:p> </o:p>
I find it hard to believe the snow ball earth theory. It seems that if it were to happen once then it would be cyclic and could happen again. I am a supporter of Milankcovitch and am not sure how his theories would fit in with the snowball earth theory.
<o:p> </o:p>
I don‚t think that much more conclusive evidence will be found for the snowball earth theory. It seems that anything found will be questionable and that a multitude of possible causes will be found. It seems like a difficult subject to prove.
Add your comments here!
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David Emerman - Re: A lot of junk after the article
3/2/05; 10:40:24 AM (reads: 30867, responses:
0) |
In this article, Hoffman discusses evidence for the theory of snowball earth. Snowball earth is the theory that at one time the whole earth was covered by a sheet of ice, including the ocean. Evidence of carbonate deposits left by glaciers was found in <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. Many causes for the evidence found are proposed including, high orbital obliquity, polar wonder, reduced solar luminosity and CO2 drawdown.
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p> </o:p>
Huffman believes that the earths tilt was greater then 54 degrees, causing longer seasons. This could be a possible explanation for the carbonate deposits found in <st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. In the end Hoffman was unable to produce any conclusive evidence. Other theories include movement of continents could produce the evidence found.
<o:p> </o:p>
I find it hard to believe the snow ball earth theory. It seems that if it were to happen once then it would be cyclic and could happen again. I am a supporter of Milankcovitch and am not sure how his theories would fit in with the snowball earth theory.
<o:p> </o:p>
I don‚t think that much more conclusive evidence will be found for the snowball earth theory. It seems that anything found will be questionable and that a multitude of possible causes will be found. It seems like a difficult subject to prove.
Add your comments here!
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David Emerman - Re: A lot of junk after the article
3/2/05; 10:40:28 AM (reads: 30839, responses:
0) |
In this article, Hoffman discusses evidence for the theory of snowball earth. Snowball earth is the theory that at one time the whole earth was covered by a sheet of ice, including the ocean. Evidence of carbonate deposits left by glaciers was found in <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. Many causes for the evidence found are proposed including, high orbital obliquity, polar wonder, reduced solar luminosity and CO2 drawdown.
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p> </o:p>
Huffman believes that the earths tilt was greater then 54 degrees, causing longer seasons. This could be a possible explanation for the carbonate deposits found in <st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. In the end Hoffman was unable to produce any conclusive evidence. Other theories include movement of continents could produce the evidence found.
<o:p> </o:p>
I find it hard to believe the snow ball earth theory. It seems that if it were to happen once then it would be cyclic and could happen again. I am a supporter of Milankcovitch and am not sure how his theories would fit in with the snowball earth theory.
<o:p> </o:p>
I don‚t think that much more conclusive evidence will be found for the snowball earth theory. It seems that anything found will be questionable and that a multitude of possible causes will be found. It seems like a difficult subject to prove.
Add your comments here!
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David Emerman - Re: A lot of junk after the article
3/2/05; 10:40:28 AM (reads: 30818, responses:
0) |
In this article, Hoffman discusses evidence for the theory of snowball earth. Snowball earth is the theory that at one time the whole earth was covered by a sheet of ice, including the ocean. Evidence of carbonate deposits left by glaciers was found in <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. Many causes for the evidence found are proposed including, high orbital obliquity, polar wonder, reduced solar luminosity and CO2 drawdown.
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p> </o:p>
Huffman believes that the earths tilt was greater then 54 degrees, causing longer seasons. This could be a possible explanation for the carbonate deposits found in <st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. In the end Hoffman was unable to produce any conclusive evidence. Other theories include movement of continents could produce the evidence found.
<o:p> </o:p>
I find it hard to believe the snow ball earth theory. It seems that if it were to happen once then it would be cyclic and could happen again. I am a supporter of Milankcovitch and am not sure how his theories would fit in with the snowball earth theory.
<o:p> </o:p>
I don‚t think that much more conclusive evidence will be found for the snowball earth theory. It seems that anything found will be questionable and that a multitude of possible causes will be found. It seems like a difficult subject to prove.
Add your comments here!
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David Emerman - Re: A lot of junk after the article
3/2/05; 10:40:34 AM (reads: 30853, responses:
0) |
In this article, Hoffman discusses evidence for the theory of snowball earth. Snowball earth is the theory that at one time the whole earth was covered by a sheet of ice, including the ocean. Evidence of carbonate deposits left by glaciers was found in <?xml:namespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" /><st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. Many causes for the evidence found are proposed including, high orbital obliquity, polar wonder, reduced solar luminosity and CO2 drawdown.
<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p> </o:p>
Huffman believes that the earths tilt was greater then 54 degrees, causing longer seasons. This could be a possible explanation for the carbonate deposits found in <st1:country-region><st1:place>Namibia</st1:place></st1:country-region>. In the end Hoffman was unable to produce any conclusive evidence. Other theories include movement of continents could produce the evidence found.
<o:p> </o:p>
I find it hard to believe the snow ball earth theory. It seems that if it were to happen once then it would be cyclic and could happen again. I am a supporter of Milankcovitch and am not sure how his theories would fit in with the snowball earth theory.
<o:p> </o:p>
I don‚t think that much more conclusive evidence will be found for the snowball earth theory. It seems that anything found will be questionable and that a multitude of possible causes will be found. It seems like a difficult subject to prove.
Add your comments here!
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George-Paul Richmann - Re: Reflection #7:Comings and Goings of Global Glaciation...
3/2/05; 12:39:39 PM (reads: 30828, responses:
0) |
What was done?
Hoffman noticed that there was an anomaly in sediment
records near in the tropics. There was a
layer of normal calcium carbonate sediment and then a layer of glacial debris
and then more calcium carbonate sediment. The author then examines several hypotheses
that could explain this anomaly settling on the idea of a Œsnowball earth≠ at
several hundred years ago, with the need for more research to verify his
results.
What were the methods?
The two main sources of data would be examining both
isotopic carbon and actual sediment layers in a region of Africa called the Otavi Platform. The result
was that the amount of isotopic carbon in the corresponding layers was indicative
of glaciation. Additionally the types of
minerals formed support glaciation.
After ruling out tectonic shifting and other hypothesis the author
showed that glaciers on the tropics support 'snowball earth'.
What was learned?
The author had two main thrusts. First, that there is evidence for snowball
earth. But secondly, because the author came
to this conclusion through the 'Sherlock Homes dictum' of disprove everything
else then what is left must be true, there really is a need for more
research.
How did this affect my thinking on the subject?
No change on my thoughts on this topic as this topic is new
to me. I was impressed with how well written
this article was.
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willis okech - Tropical Glaciation: Elimination theories
3/2/05; 10:52:08 PM (reads: 30902, responses:
0) |
The authors, Hoffman, Kaufman, and Halverson, researched on the complicated Neoproterozoic (750-543Ma) climate, which combined glacial diamicities with tropical warm-water carbonates. The suggestions of possibilities of glaciation in the tropics had earlier been disputed but strong evidence for equatorial glaciation at sea level has now been found. The authors researched into the stratigraphic relations of two Sturtian (750-700 Ma) glacial intervals by collecting detailed carbon-isotopic records from the Otavi carbonate platform on the Congo craton in Namibia. This was on the basis that these would normally be associated with warm waters. They then reviewed these based on existing contending hypotheses. These were: the high- obliquity hypothesis (>54° until the end of the Proterozoic), the inertial √interchange true polar wander hypothesis, diamicties being mega-impact ejecta hypothesis, and the ocean-overturn hypothesis.
Both self-data from the authors (detailed carbon-isotopic records), and also research from previous authors were used (the contending hypotheses).
Results showed that regional stratigraphic mapping provides no evidence of growth faulting coincident with the isotonic excursion, which might have produced anomalous subsidence rates during the Sturtian (750-700Ma) glacial interval due to insufficient time. The authors claim that one of the disputed hypotheses is consistent with their data and could explain the paradox of the Neoproterozoic climate changes.
The paper left me more confused than when I started out. I have read of past evidence of glaciation in the tropics based on fossil records for example. The high-obliquity hypothesis (>54°) is a new phenomena and I am still trying to comprehend what this could have led to. Definitely the insolation and global climates would have been altered drastically-compared to the current 23° tilt, but I don't think that this would be really justify the theory of a "snowball earth."
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Drew Ruther - If you say so!
3/3/05; 1:32:24 PM (reads: 30780, responses:
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| In this article Hoffman attempts to explain the causes of glaciation during the neoproterozoic. He states that the hypotheses for this glaciation includes increased axial tilt, polar wander, reduced solar luminosity, snowball albedo, carbon dioxide drawdown, ocean overturn, and impact ejecta.
He goes through the paper discussing the validity of each of these hypotheses. Most are viable to some extent but do not explain the data fully and leave some ambigous when it comes to fully disclosing the extent of the glaciation.
After reading the entire paper, I realized I should have just skipped to the end. This is where Hoffman says that none of the hypotheses are fully supported and that no one is sure what caused the differing sediment deposits.
What I learned from this article was that some people can really try to pull hypotheses out of their arse and you can never, ever satisy anyone completely.
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Jay Beck - AHHH ICE
3/3/05; 2:03:07 PM (reads: 30857, responses:
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The idea of glaciers being present in the areas discused do not seem to far fetched to me. However in the introduction the authors seem to present the idea of the glaciers in the neoproterozoic to be and idea that may be more fiction than fact. It isnt so much as the fact they present just the wording of the idea. If i were presenting an idea i would act as though i believed it were the gosipl and have as much confidence in my paper as possible.
I do like the area where they introduced some of the other hypothesises. I wish the were able to elaborate more on some of them (like the evidence for) especially what caused the earth be be roatating on a 54 degree axsis. I find my self confused by the paper. I read all the data, became very interested and when i was thrown the schelock holmes quote i thought by god heres gona be the answer and at least to me it seems they left me hanging. Maybe ill read it again and post another respone i i was just confused
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Kate Echement - Re #7: so....cold stone anyone?
3/3/05; 2:44:34 PM (reads: 30750, responses:
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What was done:
Hoffman et al. studied the Neoproterozoic history through the 'presence' of glaciation and global climate change. They used rock formations in Namibia and the Congo, Carbon 13 in marine carbonates, isotopic shifts, and deposition sequences.
What was learned:
They hypothesis that at one point the earth experienced a 54 degree axial tilt causing glaciation in the tropics as well as a decrease in total sun output. Basically they had a lot of hypotheses that have all been rejected. I did not understand half of the tests done, all I know is that they did not have any significant information to support any of their ideas.
What did I get out of this:
There are a lot of hypothesis concerning the Neoproterozoic intervals, and the thought of the earth reaching a 54 degree axial tilt blows my mind. Other then that, this article was very dense and hard to follow, for me at least. I had a difficult time fully understanding what all the different hypothesis were and the data they found. I found myself lost in all of the geological terms. I now understand why normal people do not believe in climate change; they cannot understand a freaking word in the scientific journal articles and other publications.
How did this article change my thinking:
Since half the time I did not understand what they were talking about, I cannot really say. It appears there are a lot of conflicting hypotheses out there attempting to explain glaciation stages. It also appears that there is much more to be done in order to examine the different eras, and what went on during those times.
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Bryan Glosik - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
3/3/05; 3:04:21 PM (reads: 30758, responses:
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The data that was collected in Namibia puts together evidence of past climate changes. Specifically, Hoffman discusses how during the Neoproterozoic Era the earth was covered in ice including the tropics. In order to come to these conclusions aspects such as polar wander, carbon dioxide levels, orbital obliquity, snow albedo, and other forms of solar impact and luminosity.
There were a couple of contending hypotheses as to why the massive glacial event occured. One proposed hypotheses is that the earth's titlt exceeded its average 22-24 degrees. Williams suggested that until the end of the Proterozoic peroid the earths obliquity was at 54 degrees. Another guess which was given was that there was a change in the polar wander. This means that there was a change in the correlation between the movement of the crust and mantle and the earths axis.
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Jacob Schober - Snowball Earth??
3/7/05; 1:39:17 AM (reads: 30768, responses:
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This article comes from Paul F. Hoffman and some associatates. This topic is truly one I've never read about before. I never thought of the entire Earth being frozen over in the Neoproterozoic era, or in any era for that matter. The retreat and advance of glaciers on a Neoproterozoic Tropical platform was discussed in this article. The authors had several hypotheses for this occurrence including: high orbital obliquity, reduced solar luminosity, true polar wonder, snowball albedo, CO2 drawdown, and stagnant ocean overturn. Their hypothesis was supported by Carbon-isotopic records. The authors make a good case for their hypothesis considering their research but I do not believe that there is truly enough data to say it is accurate. I believe that the author even states at the end that his hypothesis wasn't exactly supported by their data. This article was rather lengthy and detailed what went on in their experimentation thoroughly, because of this it was hard to interpret alot of what they were saying especially since alot of it had to do with topics i know very little about. Despite this, this article was very interesting, and taught me alot about the research process in the topic of 'snowball earth'. Prior to reading this i didnt have the faintest clue that the tropics were covered in ice at some point. The discussions on axial tilt and high orbital obliquity were especially of interest to me. The fact that all or any of the factors listed above could cause a glaciation of this magnitude is truly astounding. I never even thought that the earths axis could change because of mass distribution on the surface as is the case with true polar wonder. Overall this article was very interesting and informative. For someone more well versed in this topic it would serve as a great source for research in the topic.
-Jacob Schober-
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Shira Moskowitz - Snow and ice and why is everything nice?
3/8/05; 1:59:19 AM (reads: 30986, responses:
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Hoffman and the other scientists gathered research about reasons for the mass glaciations in the Neoproterozoic era, also known as snowball earth. There are different hypotheses that they look into and discuss in the article on reasons for there being glaciations in the tropics; some of them include the tilt and procession of the earth, orbital obliquity, solar luminosity, and the albedo of the snowball earth. They tested these hypotheses by looking at the carbon-isotopic records from the tropic zones.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com:office:office" /><o:p></o:p>
From their tests with the carbon-isotope analysis the obtained and used to support the hypothesis that there was glacier formation in the tropics, and from that they tried to figure out why and how it could have gotten there. They tested each of their hypotheses, but came out with the conclusion that none of them really supported the data in the way they thought. What that leaves them is a chance to continue to do more research on the topic and further their study.
I don‚t think I got much out of this article. They came to the conclusion that they don‚t have the answers as to why there was snow down in the tropics, however, from their carbon-isotopic analysis they do conclude that there was glacier formation in that region during the Neoproterozoic era. It's hard, I guess, to really grasp the idea that the Earth at some point was a giant snowball, when at some point in its early stages of life it was a fireball from all the many volcanoes that used to cover it. (But thats another story)
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Jason Fox - Re: Reflection #7:Comings and Goings of Global Glaciation...
3/9/05; 2:00:05 PM (reads: 30761, responses:
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Method: In this article, Hoffman looks at all the different hypotheses
that have been discussed about how global glaciation could have
happened. Hoffman takes each of these theories and uses scientific
reason why they could be implausible. He then takes a very detailed
look at his own evidence. Primarily, he looks at the data that he has
collected in the rocks of Namibia and the Congo. In these rocks, he has
found that along with the high amount of carbon that could only have
been formed in cold weather, they are topped by a completely different
level above that and is made of a different type of rock.
Conclusion: Unfortunately, his theory and other theories are still very
young. Hoffman acknowledges this when, after discrediting the other
hypostheses, he thinks that the only one to believe is his own. There
is still more information coming out about his and other theories.
However, Hoffman feels that there is some scientific evidence that most
of the planet was covered in a thick sheet of ice.
What I got out of it: Since this is my semester-long project, I already
know a good amount of this, and will learn even more about this as I
read more of Hoffman's theories and others. I think that this is going
to be very influential in the realm of science in the next few years.
This is such a wild theory, there is a good chance that it might be
true.
Will it change my thinking? I don't know yet. I have to look at more
information on this theory. Only when I have all of the information
about this theory will I decide whethere our planet was in a state of
global glaciation in our ancient history. Until then, I will just keep
researching.
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Rob - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
3/22/05; 9:43:45 PM (reads: 30695, responses:
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| Neoproterozic glaciation was discussed in detail with various hypotheses as to the inception of large-scale deposits, later verified through carbon-isotopic records. The primary goal of the article was to compare and contrast several conflicting arguments for tropical glaciation including obliquity, true polar wander, CO2 concentrations and albedo, and impact ejecta as it relates to mass-extinction and glacial signs.
The article carefully examined each hypothesis in terms of flaws in the logic and how really none of the solutions can support the carbon-isotopic findings in Namibia. Some of the techniques used to acquire data were fairly new to me including thermal subsidence analysis and sedimentation accumulation analysis where layers of rock were taken apart and examined. Carbon analyses were also used by Hoffman‚s team to better date the samples for events used to form the deposits.
I learned from this article that there still exists a huge amount of controversy surrounding the snowball earth theory (really just one of the many unique and seemingly bizarre hypotheses discussed here). I found the earth title and crazy polar wandering thing to be the most interesting as they deal with drastic global tectonic and astronomical systems changing at inconceivable rates. I believe that the idea that sea level changes were undetectable in such cases as the poles shifting 90 degrees in latitude were a novel test of this hypothesis. I feel that of all the different answers to tropical glacial deposits, the idea of mass-extinctions such as during the Cambrian, Permian, and even Cretaceous coinciding with celestial impacts seem to make the most sense. This, however, was also written off here due to some evidence in the negative-isotopic shift or whatever.
I feel that I really didn‚t get much out of the data here because I could never understand just what they were going for other than to contradict all pre-existing hypotheses. I do believe that it is important to understand this whole concept of "snowball earth" in addition to the ramifications that the theory implies especially in terms of future mass-extinction. The article did little to help clarify what else they were trying to prove other than the correlation between their findings in Namibia with some idea of global glaciation.
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Alyson - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
4/8/05; 2:55:24 AM (reads: 30703, responses:
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What was done?
Neoproterozoic glaciation hypotheses were presented in great length and technical detail. What these hypotheses mean is that equatorial regions were at one time covered with ice, which would indicate that the rest of the world would also have to be covered with glaciers (snowball Earth theory). Basically, the authors used isotopic data, lithofacies, orbital data, and much more to attempt to prove the snowball Earth theory is true. This included several theories from other authors trying to both support and decant the theory.
What was learned?
Of the several hypotheses discussed, all were basically ultimately rejected. It seems that the author is very good at deductive reasoning, and was able to systematically propose and reject hypotheses. The author is also very good at trying to present data of his own to support the snowball Earth theory, although ultimately I don't think anything was learned in the sense of proving the theory right or wrong.
What it means.
Although there is some compelling or intrigueing evidence for the snowball Earth theory, there is an equal amount if not even a greater amount of evidence going against the theory. At this point, there is not enough data to prove or disprove anything.
How it changed my thinking.
Honestly, this article was very hard to read because of its length and great technological detail. I had some difficulty understanding everything that was being discussed. It sort of left me with a frustrated feeling since all of the arguments were ultimately just to say that the theory is not true, but it is also not untrue. It is a very intersting theory, though, to think that at one point the entire Earth may have been covered with ice.
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Stanton Hugger - Re: Reflection #7:Comings and Goings of Global Glaciation......(2004)
4/26/05; 12:43:58 AM (reads: 30652, responses:
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For this reflective essay we reviewed an article by Paul F. Hoffman et
al., investigating the mass glaciations which evidently occurred during
the Neoproterozoic period. A popular slang for this phenomenon is
"snowball earth", because glaciations occurred extending all the way to
the tropics. Using data presented in the study the authors
assessed hypotheses for the glaciations in the tropics including tilt,
wobble and precession of the earth along these axis. Also solar
luminosity, planetary albedo, CO2 drawdown, stagnant ocean overturns,
and orbital obliquity are considered to be contributing variables in
the culminating glaciated earth, tilted to an axial degree as great as
54 degrees compared to our present 23.5 degrees. Using carbon-isotopic
records, the retreat and advance of glaciers along the Neoproterozoic
Tropical platform are studied, and occurrances known as "polar wander"
support the concept that isolated regions on shifting continents would
be exposed to polar regions and short term differing sea levels.
Ultimately, this is an exciting topic for me because it can be
introduced to those less exposed to climate change discourse and both
effectivey and affectively introduce them to the magnitude of forces at
work in the intricacies of climatic functioning. Cool article and
great data for backing the model of the Neoproterozoic climate, though
no sweeping evidence is available to claim most of these factors could
be affecting our more contemporary and short term climate change.
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