Talk:Gondwana
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[edit] Timetable
According to my lecturer Jørgen Klein (2004) the breakup of Gondwana is as follows: 130 Ma India breakes loose. 80 Ma Africa and South America drift apart, and Australia and antarctica some later. About 30 Ma Africa connects with Eurasia.
According to the animation on the link I've inserted the breakup is like this:
160-150 Ma: the southern part of Gondwanaland starts drifting away from South America and Africa.
120 Ma: India is disconnected, Africa starts disconnecting.
100 Ma: Africa and South America disconnect, Australia and Antartica disconnect.
90 Ma: India and Madagascar disconnect.
All this conflicts with 20-60 Ma, so I'm not sure what to trust, don't have time for more research now, but maybe later. Dittaeva 12:07, 4 Feb 2004 (UTC)
Dating of geologic events is kind of variable, because dates are given + or - so many years and such. Methods are not exact; with millions of years, people usually just aim for the ball park. They should all roughly follow though. I'll look at this; I've been editing geology articles and dating is an aspect I haven't paid a lot of attention to. I start looking for inconsistencies. If you think your dates are better, by all means put 'em in. --DanielCD 22:26, 2 Dec 2004 (UTC)
[edit] Two Gondwanas?
The present article only seems to refer to Gondwana starting in the Jurassic. However, In other articles Gondwana appears in the Cambrian period as well. Pannotia refers to Protogondwana. Can some wise person sort this out? A timeline would be helpful. The Atlantica article seems most helpful saying:
- ~Cambrian: the major supercontinent Pannotia disintegrated, leaving Atlantica in the minor supercontinent Gondwana.
- ~Permian: Gondwana, which contained Atlantica, became part of the major supercontinent Pangaea.
- ~Jurassic: Gondwana separated from Pangaea, carrying Atlantica with it.
- ~Cretaceous: Gondwana fragmented, splitting Atlantica between the modern continents of Africa and South America.
Thincat 15:53, 26 July 2005 (UTC)
- User:Jmeert has now done this. Thincat 15:29, 6 March 2006 (UTC)
The article Proto-Gondwana clarifies the point: before Merging into Pangaea (proto gondwana) and afterwards. (neo gondwana)
[edit] Location of Gondwana?
The article says, ...Gondwana was centered roughly where Antarctica is today (at the extreme south of the globe), but the illustration shows it stretching from the south pole to just north of the equator. Either the picture is wrong, or the text is. -- RoySmith (talk) 02:39, 27 December 2005 (UTC)
[edit] Gondwana merging?
This is confusing. The article on Pangea says that it split into Gondwana and Laurasia 180 MYa, but the article on Gondwana says that it merged with Laurasia into Pangea. Perhaps someone is thinking backwards in time?
[edit] Gondawan + Laurasia > Pangaea?
I think the information in this article is incorrect, or at least does not offer a complete account of the events in question. As far as i am aware, the breakup of Pangaea led to the creation of the continents of Laurasia and Gondwanaland,with Gondwanaland subsequently breaking up into the continents we know today, not Laurasia merging with Gondwanaland to create Pangaea as described in the article. I am not an expert in this field, so i cannot rewrite this article, but i think the informationn in it is wrong, and would welcome a revision of the article by someone with full knowledge of this topic.
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- I still find the article confusing, although it may be that I'm just unfamiliar with the terminology. The first paragraph suggests that Gondwana originated at the breakup of Pangaea ("a protracted process beginning with the breakup of Pangea") but the caption of the first diagram says that it was the other way around: Pangaea was formed from Gondwana merging with Laurasia. A page I found ([1]) suggests that Gondwana was formed originally from the breakup of the supercontinent Rodinia 500 million years ago, then later it merged with Laurasia to form Pangaea, then even later it broke off again, retaining its identity as Gondwana. It is a little odd that the same name, Gondwana, is used for both before and after it was part of Pangaea. At any rate the text should be consistent with the diagram caption. Mathew5000 05:08, 28 April 2006 (UTC)
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With the latest revision, the first caption states that Pangaea was formed from the "diverging" of Laurasia and Gondwana. Shouldn't that be "converging"? Or am I misunderstanding this. Also the text of the article still is not consistent with the idea that Gondwana predated Pangaea, then became part of Pangaea, then existed separately again after Pangaea broke up. --Mathew5000 04:23, 4 May 2006 (UTC)
- The conventional Gondwana = Africa + S. America + Antarctica + Australia + India - more or less existed by sometime in Late Cambrian time: [2]. Pangea was assembled by collisions among Gondwana, North America and Europe (sometimes called Euramerica) and Siberia, plus various continental plates in central and eastern Asia, though it is somewhat debatable as to how truly amalgamated the latter were to the "main mass" of Pangea. When Pangea began to break apart, the separation of most (but not all - Florida, for example, is a left-behind bit of Gondwana) of Gondwana left Laurasia as the primary "other" continent, so it is fair to say Pangea split into Laurasia plus a newly re-independent, slightly modified Gondwana. I too was confused by the caption saying Pangea was formed by diverging continents, when indeed the opposite is the case. Mathew5000 has it right. Also, it is not correct to think of any of this as occurring at specific times - as the North Atlantic began to open to separate most of Gondwana from most of Laurasia, the initial elements of the breakup of Gondwana were already beginning; it was not long (geologically speaking!) before South America began to separate as the South Atlantic opened, and some of the other rifting within Gondwana was showing the first signs of happening. --Geologyguy 22:09, 13 May 2006 (UTC)
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- I changed the caption and changed and expanded the text somewhat to try to achieve clarity and more information - have I succeeded, at least on the clarity issue? I'll work on references and better timing for the breakup of Gondwana. --Geologyguy 16:29, 15 May 2006 (UTC)
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- Yes, your revisions improved the article quite a bit. Thanks! There's a sentence that still needs some revision; either there's a word missing or it's punctuated wrong: "Gondwana was centered, in the late Paleozoic, roughly where Antarctica is today (at the extreme south of the globe), the climate was generally mild." --Mathew5000 22:53, 15 May 2006 (UTC)
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- I changed that line a bit to clarify the relations among geography, mild climate, and glaciation. --Geologyguy 00:14, 21 May 2006 (UTC)
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[edit] Gondwana Alive
The various continental plates have been moving around ever since the crust of the earth cooled and hardened. In really early days, 700 MYa, the earth was a lot smoother, making the oceans shallower, but covering up most of the earth's surface area. As they slowly began to push into each other, they started lifting in areas, predominantly in the centres of the plates (defined by fault lines). Around 600MYa, they started slowly rising, quite scattered at first, maily in the Polar Regions. These two rather small polar regions slowly started drifting towards each other, and at the same time, the compression caused more and more of what would become Pangea to rise out of the sea. It almost seems at though the polar regions then "bounced" off each other, splitting Pangea in to the northern Laurasia and southern Gondwanaland super-continents, which then again, as was correctly questioned above, split further, forming the world as we know it today.
More importantly, the Gondwanan continents, contain almost all of the worlds biodiversity. The sad thing is that over 70% of the biodiversity hotspots—the world's richest areas of floral diversity–have been destroyed by agriculture and human habitation.
Gondwana Alive, a not-for-profit organisation registered in South Africa has defined 40 corridors, across the world, where we have the richest geological heritage and floral biodiversity. We're lobbying support to have these defined as UNESCO biosphere reserves, and looking at ways in which we can protect these areas.
If you're interested, please visit the Gondwana Alive web site at http://www.GondwanaAlive.org.
[edit] Geology and climate. Why not flora
The existence of Gondwana is clearly affirmed by the floristic relationships between the modern land masses that formerly comprised the super continent. If the article contains discussions of geological and climatological development, would it not further benefit from an inclusion of a discussion of the uniqueness of this flora, and that flora's role in confirming the supercontinent's existence?
The fact that one can find Fuschias in New Zealand and Chile, Araucarias in South America, as well as throughout the Pacific landmasses, all help tell the story of what went where, when and how.
This topic is not sufficiently within my expertise to reduce it to a written component of the article. But I hope someone out there can do so.
[edit] Etymology
Gondwanaland term is derived from gond tribes in central India?
- True. It's in the article in two places. Cheers Geologyguy 19:16, 14 March 2007 (UTC)
[edit] South America
- In Gondwana#Formation and the two maps, where did the rest of South America (e.g. Argentina) come from? Anthony Appleyard 09:16, 14 July 2007 (UTC)
- The history of Patagonia is poorly understood and poorly constrained; see [3]. But it is likely that a complex of small terranes had amalgamated and was accreted to the main South American Cratons by Devonian time, perhaps by Ordovician. I've seen some things that suggest that the Cape Fold Belt may be a late-stage (Carboniferous) expression of whatever collision was amalgamating Patagonia to South America, even as West Gondwana was accreting to East Gondwana.
- The western terranes of South America - Andean, including incorporated terranes like the Precordillera - are pretty clearly later orogenic additions. Cheers Geologyguy 13:57, 14 July 2007 (UTC)
