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Antarctica Once Abutted Death Valley
Posted by
kdawson
on Sun Jul 13, 2008 08:04 PM
from the may-i-borrow-some-grey-poupon dept.
from the may-i-borrow-some-grey-poupon dept.
Science News has a story of strange bedfellows. It seems that Antarctica was once adjacent to what is now the American Southwest, some 800 million years ago. Earth's continents then formed a supercontinent called Rodinia, predating Pangaea by some 550 million years. "...the ratios of neodymium isotopes in the ancient sediments in the Transantarctic Mountains are the same as those in what was then Laurentia, says Goodge. Also, the hafnium isotope ratios in the 1.44-billion-year-old zircons found in East Antarctica match those of the zircons found in the distinctive granites now found primarily in North America. Finally, the researchers note, the ratios of various isotopes and elements in a basketball-sized chunk of granite found in East Antarctica — a chunk ripped by a glacier from bedrock now smothered by thick ice, the team speculates — match those of granite found only in what was southwestern Laurentia, which today is the American Southwest."
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but wait... (Score:5, Funny)
Re: (Score:3, Funny)
Re:but wait... (Score:5, Funny)
All those people that were here before Xenu blew them all up of course!
Parent
Re:but wait... (Score:5, Insightful)
Good point. My understanding about the theoretical pre-history of continents only went as far back as Gondwana, which dates back roughly 500 million years and is a very different map to the one in TFA, so I had a look at this [wikipedia.org] to refresh my memory and try to resolve conflicts. If TFA is true, then the continents really do shift pretty quickly and change direction a fair bit too, considering Australia started in the northern hemisphere according to TFA, went South to join Gondwana and is now heading North again.
But back to your point about how they knew what it was called, I have a related question. How do they know that Eastern Laurentia had crinkle cut coastlines like Canada? Weren't they formed by glacial activity? How does that happen at the equator?
Also, it wasn't clear to me from TFA whether the magnetic field lines conflict with this theory or support it. If they do conflict, how do we know that the distribution of isotopes isn't due to some other phenomenon?
Parent
Re: (Score:2, Insightful)
I thought the current theory was that Gondwana the resulting scar of whatever hit the earth forming the moon such a very long time ago. How many generations super continents where there?
Re: (Score:2)
Re:but wait... (Score:4, Informative)
The Pilbara region of NW Australia is one of two (the other's in South Africa) that dates back to 3.6 billion years or so. There are a few places left with intact geology, but they're far between.
Parent
Re:but wait... (Score:5, Insightful)
But back to your point about how they knew what it was called, I have a related question. How do they know that Eastern Laurentia had crinkle cut coastlines like Canada? Weren't they formed by glacial activity? How does that happen at the equator?
Most likely, they don't know that, or even think that it did. Continental drift maps are usually drawn by moving around the outlines of the modern continents for the most part, probably because that best communicates which parts went where, rather than amorphous blobs labeled things like "p.s. this is actually Canada".
My understanding would be that the actual outline of the old continents looked nothing like that and we have no way to figure out what they actually did look like.
Parent
Re:but wait... (Score:5, Interesting)
I happened to catch part of a program on the History Channel this morning that was talking about Rodinia and how the coalition of the continents into a supercontinent disrupted ocean currents, allowing the poles to become colder, expanding the continuously-frozen area until the process ran away, completely covering the Earth in ice until the eruptions that accompanied the breakup of the supercontinent threw CO2 and methane into the air that couldn't be absorbed into the oceans (covered as they were by ice), building up to the point where the greenhouse effect melted a permanent ice-free zone, which (being darker than the ice) would absorb more heat, triggering a positive feedback. The program described this happening in a single freeze-and-thaw, although some 'snowball earth' theories suggest that there were several freezovers as the CO2/methane levels rose and fell until the Cambrian Explosion. It seemed to me, though, that the arguments for Rodinia and Snowball Earth can also be explained by other theories, and that drawing conclusions about conditions that far in the past based on evidence that can accumulate in different ways is going to remain somewhat speculative.
Parent
Re:but wait... (Score:5, Informative)
Why so black and white? Just because we don't know every detail does not mean we have no way to figure out how the earths crust has changed over time. What you are missing is that to a large degree the continents sit in the middle of tectonic plates while the edges of the plates move over and under each other, coastline can change dramatically with the level of the oceans but this has nothing to do with the movement of plates or the location of the continent. Where continents do sit meet the edge of the plates you get mountain ranges. These together with ocean trenches mark the edges of ancient/modern collisions and seperations. Add evidence from fossils, the current motion of the plates, geological features, etc, and it gives you a resonable idea (ie: not a precise map) of what bits have moved where over time. The only thing that I know of where the gross features would be impossible to reconstruct are the land masses that have been subsumed back into the mantle, AFAIK this occurs mainly in deep ocean trenches and not in the middle of a continental land mass (eg: The bedrock in central Australia is ~4 billion years old, The Hawaian islands are an example of a long lived volcano in the middle of a plate).
BTW: Tropical glaciers still exist today but only at very high altitudes.
Parent
Re: (Score:3, Informative)
"Continental drift maps are usually drawn by moving around the outlines of the modern continents for the most part"
actually, no, what is primarily used is geological core examination, where they look at all the layers of rock, at the atomic decay of various isotopes, etc, etc, the idea came from someone looking at the continents, and saying it looks like Africa and south America fit together like a jigsaw piece. just the appearance alone, wasn't enough to 'scientifically' prove or date when areas were piec
Re: (Score:3, Informative)
But back to your point about how they knew what it was called, I have a related question. How do they know that Eastern Laurentia had crinkle cut coastlines like Canada? Weren't they formed by glacial activity? How does that happen at the equator?
Most likely, they don't know that, or even think that it did. Continental drift maps are usually drawn by moving around the outlines of the modern continents for the most part, probably because that best communicates which parts went where, rather than amorphous blobs labeled things like "p.s. this is actually Canada".
My understanding would be that the actual outline of the old continents looked nothing like that and we have no way to figure out what they actually did look like.
Actually, it seems to be quite a bit more complicated than just moving things around to see where they match. David Morgan-Mar had a nice rundown of one case as an annotation in irregular webcomic here [irregularwebcomic.net] (He must be really bored sometimes).
In this case, two separate places have geological and biological features that match despite being on opposite sides of the atlantic ocean, so you can well guess those features existed before separating.
Re: (Score:3, Interesting)
The coastlines on the maps are the more or less modern coastlines, superimposed on the ancient plates, purely to help orient us. I think they assume we don't take the coastlines literally.
There are lots of interesting sites with graphics of continental drift
Re:but wait... (Score:5, Informative)
As others have pointed out, the maps tend to be drawn with modern features in place to help with orientation and recognition. In point of fact, the East Coast of Laurentia probably didn't exist until 600-700 million years ago (evidence about the exact date is a bit contradictory) when one of the fractures in Rodinia separated Laurentia from Gondwanaland by opening up an ocean called the Iapetus Sea. The Iapetus subsequently closed in a complicated series of events starting about 460 million years ago and then opened up again on a sort of parallel line in the Triassic forming the modern Atlantic. We (think) we know where the East coast of Laurentia was because there is a quite distinctive geologic boundary called Emmon's (Logan's) Line that can be traced from Newfoundland to Georgia where Iapetus sea sediments were pushed up into/onto Laurentia as the Iapetus Sea closed. There are a couple of zigs and zags in Emmons line -- one NW of New York city and one SE of Montreal -- but mostly it follows the course of the Appalachian mountains and lies a bit West of the Easternmost range of the mountains.
Parent
Re:war history (Score:4, Funny)
Parent
Re: (Score:2)
Aw, that's easy. Search Google for Dropa Stones, Phaistos Disc, Bi disks [wikipedia.org] (linked for clarity), Arkalochori Axe, Anatolian hieroglyphs, Gobekli Tepe, Egyptian hieroglyphics, and Pnakotic Manuscripts.
If that doesn't get your head spinning with conspiracies, start thinking about how much was probably destroyed through action or negligence over the centuries. You also have to consider much of this was not found or understood until recently. What will we find about the past in the next 100 ye
Re: (Score:3, Funny)
hey, it was McCain's old stomping grounds.
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Re:but wait... (Score:4, Informative)
IIRC it's not all that odd at all. Russians are allowed to have a few scientists going around naming things if they want. Wikipedia (which may be my original source) agrees with me: "In geology, Rodinia (from the Russian [rodina], or 'motherland') ..."
Parent
Re: (Score:3, Funny)
... how do we know it was called Rodinia?
What else would you call a place with a gaggle of Rodinians nobbing about?
Re: (Score:2, Redundant)
Hmmmm.... (Score:2)
Something makes me want to go and re-read H.P. Lovecraft's At the Mountains of Madness.
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http://www.dagonbytes.com/thelibrary/lovecraft/mountainsofmaddness.htm [dagonbytes.com]
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A sociopath, a communist and a moron? What's not to love!
Death Valley is a bitchin place (Score:5, Funny)
Go spring or fall... crank up the Harley and pack some doob... bring a camera... stuff your ugly bitch in the seat behind you... and stay at Panamint Springs (the other places are run by contractors with federal NPS contracts).
There is NOBODY there. It's a space as big as Connecticut and you have it all to yourself and maybe a few dozen other people. After a few days you start to recognize them; you even start waving at each other when you pass. It's totally like Antarctica.
Re:Death Valley is a bitchin place (Score:5, Funny)
Fine. One of the reasons there's nobody there is because of all of the assholes on their Harleys :)
Parent
Re: (Score:2)
Where, Antarctica or Death Valley?
Re:Death Valley is a bitchin place (Score:5, Funny)
One of the reasons there's nobody there is because of all of the assholes on their Harleys :)
Taken literally or figuratively, the visuals are not appealing.
Parent
Re:Death Valley is a bitchin place (Score:5, Insightful)
True, and I know lots of Harley riders, most of whom are very nice. However, anyone who rides an unmuffled motorcycle and is proud of its noise is, by definition, at least an inconsiderate jerk.
Parent
Re: (Score:3, Interesting)
Another phrase is "douchebags who made their bikes as loud as possible kept waking up our baby and drove us out of our house".
If my wife thought she could get away with it, her phrase would be "loud pipes will meet the piano wire I've strung across the street".
Re:Death Valley is a bitchin place (Score:5, Insightful)
Besides, if being noticed is a problem, why is the standard-issue biker uniform an oh-so-visible black?
Parent
Re: (Score:3, Funny)
It's totally like Antarctica.
Except it is a dry heat, ya'know.
Re:Death Valley is a bitchin place (Score:5, Funny)
That's why Death Valley is so hot. Antarctica got all the cold in the divorce settlement.
Parent
Re:Death Valley is a bitchin place (Score:5, Funny)
... stuff your ugly bitch in the seat behind you...
Do I have to take the ugly one?
Parent
Re: (Score:3, Insightful)
left no forwarding address (Score:4, Funny)
Damned landmasses, moving around all the time.
Plate techtonics are breaking up that old neighborhood of mine.
Re:left no forwarding address (Score:5, Funny)
Parent
Legal implications? (Score:2, Funny)
Does this mean that the United States has a historical claim to Antarctica?
How many supercontinents were there? (Score:3, Interesting)
I was quite surprised when I learned several years ago that Pangea wasn't the only one. Could someone well-versed in geology fill us in here?
-jcr
Re:How many supercontinents were there? (Score:5, Informative)
The oldest one proposed is called Columbia, existing from 1.8 - 1.5 bya.
The next widely accepted was Rodinia, existing from 1.3 bya - 800 mya
The next possible was Pannotia, but it didn't last long, only from 600 - 550 mya.
The last one was Pangaea, from 250 mya to 150 mya.
The earliest ones are deduced mainly from paleomagnetism, so there may have been earlier supercontinents that we do not know about due to a lack of rocks that old.
Parent
Re:How many supercontinents were there? (Score:4, Informative)
Wikipedia talks about Vaalbara, Ur and Kenorland predating Columbia, which was then followed by Rodinia, Pannotia, Pangaea, Laurasia and Gondwana.
This was all unknown to me until about ten minutes ago, but I'm pleased to see the Pilbara region of Australia (my country) is one of the oldest places on Earth, stretching back 3.6 billion years (the other's in South Africa).
I guess that if you can date the geology, you can talk about the continents, but their shape must be a bit of a mystery.
Parent
explains a lot. (Score:5, Funny)
Maybe the Cubs won the World Series that year...
Antarctic joke (Score:3, Interesting)
A few days later, the first thing the geologist sees when he reaches the area is of course this rock. He aborts his trip, comes back to the main base all excited about some revolutionary theory or other and starts writing feverishly about it. It took us a bit of courage to tell him the truth and deflate him... He was able to go back to his advanced camp, but it proves that it can be too easy to fake/mistake data in some cases.
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did anyone else miss read that and think "When did Google start crawling archaeology?"
Re: (Score:3, Funny)
A better questions is: You mean they don't? WTF, somebody call Mr Brin! This is a serious oversight. I've been hankerin' to trawl me through some archeology street views, I want to see those humans that lived with dinosaurs.
Re: (Score:2)
You're thinking of "aboot".
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Totally offtopic...
I once told a long lost acquaintance that "you have that 'o' thing goin' there, dontcha?"
She was 'orrified, guvna. Really 'orrified. She only thought that Newfies really had it.
She was from Haligonia.
--
BMO - goin' aboot in a boot.
Re: (Score:3, Interesting)
Just because you confuse "theory" (argument supported by facts) and "hypothesis" (educated guess) doesn't mean that other people are wrong and that people who do science are talking out their asses.
This is exactly like the retard^W Creationist argument that "I've never seen any animal evolve into another species" totally ignoring what is actually /meant/ by the accepted definition of "species" while the retard^W Creationist uses his own private definition of "species".
You argue without and against reason, a
Re:Umm... Shouldn't This Be Obvious? (Score:5, Informative)
Actually, the continents are different from the sea floors, and not just because of the water. They do in fact "float around like rafts" over the sea floors, creating new sea floor behind them and pushing it down below them in front into trenches. The sea floors are much younger than land surfaces for that reason.
Parent