Dear Cecil,
Maps always show continents drifting away from Antarctic. Has Antarctic ever drifted, and if so in what direction ? Maps also show India abutting against Eurasia, thus uplifting the Tibetan plateau. Question: Is Eurasia in a steady state ? If some continents don’t drift, do we know why some do and some don’t ?
Michael D.
Gymnopithys-
Welcome to the Straight Dope Message Boards!
This forum is for comments on columns by Cecil Adams that have already been published on this website. If you are referring to a specific column with your thread, please include a link.
I suspect, however, that you are posting a new question for Cecil to answer. Cecil doesn’t check this forum for new question submissions. That is best done through the e-mail link that can be found on the Straight Dope Homepage, where it will be included in the vast heap of mail that he or one of his assistants may choose to answer. Or not.
If you’re looking for a quicker answer to a question, I suggest posting the question in the General Questions forum, where any number of Straight Dope Message Board subscribers (Dopers, of whom you are now one), may be able to get things straight for you. On rare occasions, a column is drawn from a thread there.
Again, assuming this is a new question, I’ll give what I know from my limited knowledge of geology, and alert the mods to possibly move the thread to GQ if you don’t post a link.
If you look at a map of the world showing tectonic plates, you usually see the plate boundaries with opposing arrows on either side of the line. This reflects our relative lack of knowledge of just which plate is moving how fast in what direction at that part of the boundary. All we usually know is the relative motion of the plates to each other. Over time, with more data this may change.
For example, there’s a certain amount of confusion about what is happening with the Pacific Plate in the region of South America and Antarctica. It is my personal hypothesis that data gained from this area will eventually enable us to get an “absolute plate velocity” map. For now, such a map eludes us, to the best of my knowledge.
Again, welcome and have a good time!
Echoing scotandrsn’s comments about proper forums, I’m moving this to the forum called “General Questions.”
Welcome to the Straight Dope Message Boards, Gymno. You might want to take a few minutes to acquaint yourself with the different forums.
Cool user name. Which species?
Since the breakup of Pangea, the continent that has probably been on average closest to its present position is probably Africa. Antarctica has moved substantially since the Jurassic. See here. Which continents move, and which stay relatively still, depends largely on the positions of oceanic spreading centers. Since Africa was nearly in the center of the the Pangea land mass before it broke up, other continents have tended to spread away from it.
The former positions of continents are in part worked out by magnetic signatures embedded in rocks when they form. Without going into too much detail, these indicate the position and distance of the pole at the time of formation. When the rocks are dated, this indicates the position of the continent at the time.
You ight also want to check out some of the inforatin and further links provided in the recent thread Gondwanaland, Pangea and You.
I have got to get this m key fixed.
I recall reading, some time ago, that Madagascar is the Gondwanaland remnant with the least tectonic motion – that it is today very near to where it was when it was a part of the supercontinent.
Any truth to that?
Assuming the animation I linked to is accurate, then Madagascar may in fact have shown the least net movement from its original position in Gondwanaland. However, at least according the the animation its actual movement seems to have been considerable – it just happened to end up where it started out in the Jurassic.
With reference to the OP, besides ancient magnetism, another method that has been used to identify the former position of plates is the tracks of “hotspots” such as the Hawaiian Islands, the Galapagos, and Yellowstone. The position of these volcanic centers relative to the Earth’s core and to each other is thought to be stable for many millions of years. As the plates move above them, the eruption of volcanic materials from the hotspots provides a track that records the direction and speed of plate movement.
[QUOTE=Colibri]
Cool user name. Which species?
When trying to log in I got tired seeing that my chosen pseudonyms were all preoccupied. So I opened haphazardly Howard & Moore’s Complete checklist of the birds of the world, third edition 2003, and found the name at the top of the page 393. The species is leucaspis which is found in Panama. Which subspecies ? You decide wether it is olivascens in the west, or bicolor in the east.
Since the breakup of Pangea, the continent that has probably been on average closest to its present position is probably Africa. Antarctica has moved substantially since the Jurassic. See here. Which continents move, and which stay relatively still, depends largely on the positions of oceanic spreading centers. Since Africa was nearly in the center of the the Pangea land mass before it broke up, other continents have tended to spread away from it.
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All answers helpful, but scotese site is really enlightning.
Signed: DNA (Dope New Addict)
Thanks scotandrsn. Please pardon my inexperience.
A question: When first checking the responses to my query, I saw a number of intelligent answers. But they disappeared ! They are not in “General Questions”. Where did they go ?
I have no idea. The numbering of responses seems to be ordered. I didn’t read the thread that well, so I don’t know what’s missing. I’ll have someone check to see if something wonky happened.
To my knowledge, there was certainly no deliberate moderator intervention to make any posts disappear…
I have not seen any moderator action directed at this thread (aside from Dex’s initial move from CoCC that seems to have arrived intact). Is there any possibility that you rviewed the Pangaea thread to which I linked in post #5 and are now simply not recalling having jumped over to that thread and back?