This post spawned out of reading Continents and Supercontinents which I picked up via Amazon. It was a good, if a bit higher in its expectations of the reader than the average book: it out right states its intended for grad students and pros in the geo field. The reason that I picked it up was to try to understand, at least a bit more, what-how-why supercontinents form and the consequences of their existence. I got a bit of that. I get the distinct feeling that studying the past supercontinents is really a newish affair and still hasn't reached the level of detail I'd hoped for. That said, I did get some rather juicy bits I thought I would share.
The first of those is the cycle that seems to exist for supercontinents that at least to date appears to hold true. Whether it will in the future or not, I cannot say. The book did discuss the future of supercontinents in the form of Amasia - we'll get to that later - but not whether or not the cycle supercontinents go through would slow or stop as the planet 'ages' and cools. So what is the cycle? Supercontinents seem to go through three distinct periods: assembly, existence, and fragmentation. The assembly period takes 500 million years! The existence appears to last a mere 100 million years. Fragmentation takes another 200 million years. It appears to be have been presented in papers in the past as the supercontinent cycle. This cycle has been observed in the geological record at least three times with high levels of confidence and once more at least being suspected.
The first time that we suspect that the assembly, existence, and fragmentation of a supecontinent happened was so far in the past that it is considered very sketchy as far as the evidence is concerned and as a consequence is at least moderately controversial. At least more so than the other supecontinents that have been proposed so far. Unfortunately, this earliest of supercontinents remains unnamed at this point but it is believed to have existed in the Late Archean and early Proterozoic. This supercontinent was proposed only recently (2003) and so is still being debated and fleshed out.
The second supercontinent, moving forward in time, was Columbia. This supercontinent achieved its largest size supposedly around 1.6 billion years ago during the Statherian.
The third supercontinent was Rodinia. Clocking in during the Tonian and Cryogenian, Rodinia started forming 1.3 billion years ago and lasted until 800 million years ago when it too began to rift. Interestingly, this is one of the most controversial supercontinents, but I am a bit at a loss as to why. I suspect that it is because of the proposed relations to the Snowball Earth hypothesis - and the suggestion that supercontinents are the source of ice house climates - but that's just a guess.
The last true past supercontinent that the book talks about is Pangaea. This one assembled and then rifted during the Triassic. The height of its glory was really in the Permian though and the frustrations that it visited on paleontologists due to its less than friendly environment that it created for fossil preservation is quite well known. It ought to be noted that Gondwana was a fragment of Pangaea and ought to be considered as such. More or less.
Amasia was the only supercontinent of the future that was talked about at all. This would be the assembly of a new supercontinent by North America colliding with Asia while Australia, Africa and South America continue their marches north. Amasia is based on the premise that the Atlantic will continue to expand and the Pacific will be ultimately swallowed up. This is in contrast the the Pangaea Ultima proposal such as Dr Scotese's.
Anyways, there are some notes from reading. It was an interesting if a bit more demanding than I expected (but not too difficult). I do recommend picking it up, but I do recommend keeping wikipedia and a geological dictionary handy. Oh, one nasty bit aimed at the publisher: the cover is frakkin upside down. I take the dust jackets off since they get ripped up and you have no idea how often I mistakenly picked it up title up. grr.
The first of those is the cycle that seems to exist for supercontinents that at least to date appears to hold true. Whether it will in the future or not, I cannot say. The book did discuss the future of supercontinents in the form of Amasia - we'll get to that later - but not whether or not the cycle supercontinents go through would slow or stop as the planet 'ages' and cools. So what is the cycle? Supercontinents seem to go through three distinct periods: assembly, existence, and fragmentation. The assembly period takes 500 million years! The existence appears to last a mere 100 million years. Fragmentation takes another 200 million years. It appears to be have been presented in papers in the past as the supercontinent cycle. This cycle has been observed in the geological record at least three times with high levels of confidence and once more at least being suspected.
The first time that we suspect that the assembly, existence, and fragmentation of a supecontinent happened was so far in the past that it is considered very sketchy as far as the evidence is concerned and as a consequence is at least moderately controversial. At least more so than the other supecontinents that have been proposed so far. Unfortunately, this earliest of supercontinents remains unnamed at this point but it is believed to have existed in the Late Archean and early Proterozoic. This supercontinent was proposed only recently (2003) and so is still being debated and fleshed out.
The second supercontinent, moving forward in time, was Columbia. This supercontinent achieved its largest size supposedly around 1.6 billion years ago during the Statherian.
The third supercontinent was Rodinia. Clocking in during the Tonian and Cryogenian, Rodinia started forming 1.3 billion years ago and lasted until 800 million years ago when it too began to rift. Interestingly, this is one of the most controversial supercontinents, but I am a bit at a loss as to why. I suspect that it is because of the proposed relations to the Snowball Earth hypothesis - and the suggestion that supercontinents are the source of ice house climates - but that's just a guess.
The last true past supercontinent that the book talks about is Pangaea. This one assembled and then rifted during the Triassic. The height of its glory was really in the Permian though and the frustrations that it visited on paleontologists due to its less than friendly environment that it created for fossil preservation is quite well known. It ought to be noted that Gondwana was a fragment of Pangaea and ought to be considered as such. More or less.
Amasia was the only supercontinent of the future that was talked about at all. This would be the assembly of a new supercontinent by North America colliding with Asia while Australia, Africa and South America continue their marches north. Amasia is based on the premise that the Atlantic will continue to expand and the Pacific will be ultimately swallowed up. This is in contrast the the Pangaea Ultima proposal such as Dr Scotese's.
Anyways, there are some notes from reading. It was an interesting if a bit more demanding than I expected (but not too difficult). I do recommend picking it up, but I do recommend keeping wikipedia and a geological dictionary handy. Oh, one nasty bit aimed at the publisher: the cover is frakkin upside down. I take the dust jackets off since they get ripped up and you have no idea how often I mistakenly picked it up title up. grr.
2 comments:
Rodinia started forming 1.3 million years ago [...]
Should that "million" be "billion"?
doh.
yes.
thanx for the catch.
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