December 7, 2000

3:13 PM

About 250 million years ago all of the continents were joined in a single land mass called Pangea. Then they broke up and drifted apart to their present positions. Plate tectonic projections forecast that 250 million years from now, the continents will once again join up into a single land mass now dubbed Pangea Ultima. JRR Tolkien couldn't have dreamt up a better Middle Earth.
posted by lagado (16 comments total)

Incidentally, Pangea wasn't the first supercontintinent. They have occurred serveral times. The earliest that has been reconstructed from the geological record is called Rodinia which formed 1.1 billion years ago. That broke up 750 million years ago and reformed into a new supercontinent named Pannotia. Pannotia then broke up into what became two supercontinents Laurasia and Gondwana. These two then joined approximately 275 million years ago to form the supercontinent of Pangea.
posted by lagado at 3:58 PM on December 7, 2000

Okay, what I've always wanted to know and have never seen covered anywhere is this: were there other landmasses?

I find it tough to believe that when Pangea existed that it was the ONLY landmass, all lumped up on one side of the planet, with the entire rest of the globe being ocean.

Doesn't it just seem like common sense that there were other continents or islands on plates that have been sent back underwater (or into the earth) as Pangea broke up into what we know today?

I suppose that it would be nearly impossible to tell, but this question just jumps to mind every time I see that lopsided-looking image of Pangea.
posted by kokogiak at 4:17 PM on December 7, 2000

Well, I wonder if I'm going to be asking 250 million years from now 'Gee, wow, whatever happened to North America?' 'Ohh yeah'
posted by tiaka at 5:12 PM on December 7, 2000

The reason for the concentration of the land on one side of the planet has to do with how the moon was formed.

Earth suffered a glancing impact or very near miss with a body which may have been the size of Mars, and the encounter knocked a considerable portion of the planet off. Eventually all of that coalesced into Luna, which is why Luna is the most unusual moon in the Solar System. (The moon appears to be made primarily out of material similar to the crust and upper mantle of the Earth, but with little or nothing resembling the Earth's deep core. That's why Luna has no magnetic field and why a compass won't work there.)

That also left the Earth unbalanced, which it has remained to this day. The floor of the Pacific is different than the floor of the Atlantic. Water, being able to flow, filled in the deficit and restored the overall body to approximate sphericity, since of course water flows down.

But the answer is, no other continents existed because the material to form them had been knocked into space.

Or so I understand it.
posted by Steven Den Beste at 6:23 PM on December 7, 2000

I saw someone one time wearing a T-shirt which read "Re-unite Gondawanaland" and I gave him a knowing grin.

He told me that a lot of people thought that it was some sort of protest about things going on in Africa.
posted by Steven Den Beste at 6:25 PM on December 7, 2000

Damn! Steven got the T-shirt one first.
posted by dhartung at 6:59 PM on December 7, 2000

that lopsided-looking image of Pangea

The world is still pretty lopsided even today. Most of the land is locked up into Eurasia/Africa.

posted by lagado at 7:46 PM on December 7, 2000

<stupid joke>
So how do they know it was called Pangea?
</stupid joke>
posted by davidgentle at 8:18 PM on December 7, 2000

Well, actually wasn't the land mass that became the moon called "Gonewiddawind"?

Ba dum bum.
posted by ethmar at 8:34 PM on December 7, 2000

Good to see the Appalachian Mountains are (still) there. This will be like the 6th or 7th mountain range to form independently along the same spot.
posted by stbalbach at 9:09 PM on December 7, 2000

Steven, do you have any cites for that account? It doesn't fit with any of the accounts of moon formation I've heard (except for this one).
posted by rodii at 9:30 PM on December 7, 2000

It came from a program I watched on the Discovery Channel. Sorry. Tomorrow when I'm less fogged, I'll try to search around and see what I can find.
posted by Steven Den Beste at 9:54 PM on December 7, 2000

The collision theory is pretty much the accepted one for the formation of the earth's moon.

I'm not so sure about this also being the cause of the continent formation though.
posted by lagado at 3:00 AM on December 8, 2000

"About 4.45 billion years ago, a young planet Earth -- a mere 50 million years old at the time -- experienced the largest impact event of its history. Another planetary body with roughly the mass of Mars had formed nearby with an orbit that had, by chance, placed it on a collision course with Earth. When young Earth and this rogue body collided, the energy involved was 100 million times larger than the much later event believed to have wiped out the dinosaurs. The early giant collision destroyed the rogue body, likely vaporized the upper layers of Earth's mantle, and ejected large amounts of debris into Earth orbit. From this debris our moon coalesced, possibly on a time scale as short as one to 100 years. " -- Big Bang, New Moon

Other sites:

The Origin of the Moon
Lunar Prospector Data Supports Moon Origin Theory
Theories for the Formation of the Earth's Moon
FORMATION OF THE MOON
Scientists Explain Tilt of Moon's Orbit

posted by lagado at 3:57 AM on December 8, 2000

A (very outdated) world atlas I saw depicted a theory where the Earth used to be smaller than it is now, and the continents fit together around a smaller sphere, without much water. Then the sphere expanded and the continents split apart. Very dubious theory, but the puzzle pieces did fit, so it was interesting.
posted by girlhacker at 10:54 AM on December 8, 2000

Thanks, all. I know the collision theory for the formation of the moon, I had just never heard it invoked to explain the distibution of the continents before. The time scales seem completely out of sync--we've had several distinct episodes of breakup and recombination since the birth of the moon, haven't we?

It's interesting to look at continent formation in detail. There are all these little microcontinents around that get "swept up" by the big boys and form terranes within modern continents. (See the last section of McPhee's magnum opus for some on this.) It's kind of a different image than the classic Wegener puzzle-pieces model.

Some nice animations here.
posted by rodii at 12:28 PM on December 8, 2000