RE: On The Rise of Oxygen...
Much more like stromatolites; where small individual components assemble large structures, much of which consists of nonliving matter... try to imagine a highly skeletal kelp, conceivably hundreds of metres long; with the bulk of mass a nonliving support structure. A jellyfish is a paradigm of complexity by cf. * 2m dragonflies could glide effectively in modern atmospheric conditions if there wasn't anything else around to eat 'em. Large dragonflies survived deep into the Mesozoic; & overlapped slightly with the first pterosaurs... one should note, however, that there are two planes of threat to flying critters: one is other flyers; the other is improved predators which can attack you on the ground All the best, Robert Clements <[EMAIL PROTECTED]> > -Original Message- > From: [EMAIL PROTECTED] [SMTP:[EMAIL PROTECTED]] > Sent: Saturday, December 09, 2000 4:50 PM > To: [EMAIL PROTECTED] > Subject: Re: On The Rise of Oxygen... > > A giant Europan jellyfish might be the prototype, then. Something large > enough to be able to absorb energy across a broad area (say, 1 km across). > > Freezing or ice shifts might only kill off a section of it, quickly > regenerated. All speculative of course. Probably lousy eating. * > Same goes for dragonflies. I'd think they would simply need thicker air > to > supply loft to those inefficient wings. > > Could the pterosaurs have been their end? I dunno... because in the > transition interim from developing from hoppers to flyers, wouldn't they > still be easy meat for those 2' dragonflies? Dragonflies are, after all, > voracious predators, with jaws that can chew up insects far larger than > they > are. > > -- JHB > == > You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] > Project information and list (un)subscribe info: http://klx.com/europa/ == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
RE: On The Rise of Oxygen...
Well - no sauropods grew 100ft tall (although a few were more than 100ft long); & they were more of a design which which would allow such a shape to develop. I did include a proviso _all other things being equal_; & the bigger you get, the less the carrying capacity of any environment. Add the cost factors involved in the ability to internally regulate body temperature; & the carrying capacity of an environment becomeas more limited still. Crocodylians - which have no internal body temperature regulation & in theory never stop growing - don't appear to have grown any larger than the admittedly spectacular purosaurus (Cainzoic; Amazonia); which was 15+m & 5-10metric tons of really bad scale day All the best, Robert Clements <[EMAIL PROTECTED]> > -Original Message- > From: [EMAIL PROTECTED] [SMTP:[EMAIL PROTECTED]] > Sent: Sunday, December 10, 2000 9:13 AM > To: [EMAIL PROTECTED] > Subject: Re: On The Rise of Oxygen... > > Then why didn't Imperial Mammoth grow 100' tall, especially when in cold > climates such as an Ice Age, it would be a benefit? I suppose that steppe > > grasses will only take you so far... > > On the other hand, perhaps the combination of high body mass AND internal > temperature regulation would lead to overheating? Perhaps the brontothere > > and titanothere had a danger of heat exhaustion? > > == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
<< (Bear in mind, too, that some of the brontotheres of the mid Cainozoic were pretty weight competitive with at least the smaller sauropods. No doubt the brontotheres were something less than wildly active; but this shows that sauropodian mammals - while probably less likely than their dinosaurian counterparts - were not completely impossible) Then why didn't Imperial Mammoth grow 100' tall, especially when in cold climates such as an Ice Age, it would be a benefit? I suppose that steppe grasses will only take you so far... On the other hand, perhaps the combination of high body mass AND internal temperature regulation would lead to overheating? Perhaps the brontothere and titanothere had a danger of heat exhaustion? tells us clearly is that it _wasn't_ a change in environmental conditions which doomed the giant sauropod line: it was competition (in Siberia, China & NAmerica) & finally the Chicxulub impact (everywhere else) which did 'em in. Gary Larson suggests it was cigarette smoking that did in the dinosaurs. Another good eg of this phenomenom at work is amboreiser, the enormous (& i do mean enormous: some where the size of small bears) rat of greater Anguilla. No unusual atmospheric situation here; just a total lack of competition, so that a few, probably wet & highly bedraggled rattus rattusi grew very big very fast. Now THAT, I am interested in reading about... So, you're saying that the fabled R.O.U.S. of 'Princes Bride' fame is alive and well, and hunting for large wheels of cheddar cheese on Anguilla... hmmm -- JHB == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
In a message dated 12/8/2000 5:28:26 PM Alaskan Standard Time, [EMAIL PROTECTED] writes: << >This has a strange relevance to Europa, however. If life exists in the >Europan ocean, it's likely to be living in a low energy environment where >competition is unlikely to be widespread. Unlike most people, therefore, >i don't rule out the possibility of really large life forms there; but >would still expect them to be expect them to be extremely primitive > It should be pointed out, however, that multicellular organisms never evolved on Earth at all until the evolution of photosynthesis provided them with a much more efficient energy supply -- so it still seems overwhelmingly likely that all Europan life will be single-celled unless large amounts of photosynthesis are possible in water pockets or cracks very close to the surface (and that is an extremely big "if"). A giant Europan jellyfish might be the prototype, then. Something large enough to be able to absorb energy across a broad area (say, 1 km across). Freezing or ice shifts might only kill off a section of it, quickly regenerated. All speculative of course. Probably lousy eating. (And, by the way, there's a surprising amount on the weta available on the Web -- it turns out to be a huge cricket. Apparently its maximum length is 90 mm, though -- which, I think, is still somewhat smaller than the African Goliath beetle and maybe one or two other huge insect species as well.) >> There's a similar cricket in Mexico. When I lived in Northern Mexico (the Sonoran desert) I often saw immense 4" crickets creeping across the roads. Very brightly colored, they were so slow I often wondered how they could survive cars and predators. I still say that in order to be competitive, they'd need O2 supercharging. Same goes for dragonflies. I'd think they would simply need thicker air to supply loft to those inefficient wings. Could the pterosaurs have been their end? I dunno... because in the transition interim from developing from hoppers to flyers, wouldn't they still be easy meat for those 2' dragonflies? Dragonflies are, after all, voracious predators, with jaws that can chew up insects far larger than they are. -- JHB == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
Bruce Moomaw wrote: > > It should be pointed out, however, that multicellular organisms never > evolved on Earth at all until the evolution of photosynthesis provided them > with a much more efficient energy supply -- so it still seems overwhelmingly > likely that all Europan life will be single-celled unless large amounts of > photosynthesis are possible in water pockets or cracks very close to the > surface (and that is an extremely big "if"). Only if you think in terrestrial terms. One possibility which springs to mind would be a large colonies, perhaps even of subcellular creatures, assembled on long strands of nonliving matter: horizontal stromatolites, if you like. In the absence of competition & with the primary need to collect as much nutrient from the Europan ocean as possible, these could grow extremely long while still being organically incredibly simple. All the best, Robert Clements <[EMAIL PROTECTED]> == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
Bruce Moomaw wrote: > > What in the world is a weta? Answered elsewhere; but a really big NZ bug. Can't kill you, though... the weta lives in NZ not Australia (Private joke) > More generally, in today's lower-oxygen environment, big bugs must be much > more sluggish, which puts them at a severe disadvantage both in chasing prey > and in surviving predation themselves. A few of them still hold on in very > specialized ecological niches, but it still seems overwhelmingly likely that > what wiped out almost all of them -- either directly or indirectly -- was > that O2 loss. (Note, by the way, that almost all the surviving big > arthropods are aquatic, simply because they don't have to carry their own > weight around.) What this tells us is why arthropods struggle to survive in a competitive environment; but doesn't actually address the original point: whether such critters were impossible in contemporary conditions. One could conceive of niches even now where a large, sluggish megacockroach could survive in the same way that ancient stromatolites still survive in West Australia; & while i'm not going so far as predicting that a full census of the critters which skitter in, on & over this planet will turn up a Paleozoic style 1m roach, you can't sat that it's physically impossible. (You CAN say that it's unlikely; & i completely agree with that assessment) > I just had a thought: Would the higher O2 level of the Permian mean that the > worldwide fires set by an asteroid impact would be much more severe back > then -- and could this possibly explain why the Permian extinction was so > much more complete than the Cretaceous one? (It wouldn't directly explain > why the Permian marine extinction was also worse; but maybe the increased > smoke -- and the resultant natural "nuclear winter" effect -- would also > have been more severe.) > > Bruce Moomaw Probably not on its own. The Permian extinction is far more cluttered than the nice, neat hit of Chicxulub & life was more monocultural than it was at the end of the Cretaceous (the Jurassic park image of Cretaceous - there's hardly any Jurassic critters in any of the Jurassic books or films - is very much restricted to what we've found in NAmerica, China & Siberia); with the formation of the ultimate supercontinent Pangaea causing considerable climactic changes on its own; over which is laid massive volcanism (related to the Pangaea formation); a probably asteroid strike; & a plunge in O2 levels (which is likely to be related to one or more of the previous events). The Permian extinction event was a really nasty time to be alive; & only one major critter survived it: the beloved Lystrosaurus... a really ugly therapsid (mammallike reptile) which looked a bit like a cross between a Komodo Dragon & a pig; & sure enough: the Lystrosaurus Interlude (as it's known in palaeontontological circles) saw the lystrosaurs grow to enormous sizes until competition from the reptiles wiped them out. All the best, Robert Clements <[EMAIL PROTECTED]> == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
-Original Message- From: Robert Clements <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Cc: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Date: Friday, December 08, 2000 6:11 PM Subject: Re: On The Rise of Oxygen... >This has a strange relevance to Europa, however. If life exists in the >Europan ocean, it's likely to be living in a low energy environment where >competition is unlikely to be widespread. Unlike most people, therefore, >i don't rule out the possibility of really large life forms there; but >would still expect them to be expect them to be extremely primitive > It should be pointed out, however, that multicellular organisms never evolved on Earth at all until the evolution of photosynthesis provided them with a much more efficient energy supply -- so it still seems overwhelmingly likely that all Europan life will be single-celled unless large amounts of photosynthesis are possible in water pockets or cracks very close to the surface (and that is an extremely big "if"). (And, by the way, there's a surprising amount on the weta available on the Web -- it turns out to be a huge cricket. Apparently its maximum length is 90 mm, though -- which, I think, is still somewhat smaller than the African Goliath beetle and maybe one or two other huge insect species as well.) Bruce Moomaw == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
Jayme Blaschke wrote: > > >>>What in the world is a weta? > > Director Peter Jackson's Wellington-based SFX company. :-) > > Jayme Lynn Blaschke No great surprise... Jacko's a Kiwi (New Zealander); with a taste for cinema almost as ugly as the weta itself. The weta is a very large arthropod endemic to NZ & surrounding islands; & as such is most unlikely to win any animal beauty contests (in fact, it looks a little like a mutant cross between a cockroach & a crab). As Bruce pointed out - & i acknowledge - being a large hard shelled critter puts you at a serious disadvantage in a mature ecosystem; but the NZ - even more than Australia - was ecologically very isolated prior to the arrival of the Melanesians (now Moari) people less than 1000yrs ago... as a result, the normal rules of competition didn't apply here; & insects like the weta & large, flightless birds like the tuatara, moa, kiwi & kakapo survived quite comfortably. To reconcile my position with Bruce's observations: there's no doubt that some bodily systems are more efficient in the contemporary environment than others; but that isn't the same as saying that - in the absence of competition from more efficient living systems - large cockroaches mightn't reappear in contemporary conditions. Indeed: they almost certainly would (following the bigger is better principle); & the palaeontonological Lystrosaurus Interlude (immediately following the Permian extinction; where a single therapsid called the Lystrosaurus which survived the extinction dominated the environment for about 10my) would be matched by a new Cockroach Interlude, as these enormous roaches essentially waited for better designs to supplant 'em. This has a strange relevance to Europa, however. If life exists in the Europan ocean, it's likely to be living in a low energy environment where competition is unlikely to be widespread. Unlike most people, therefore, i don't rule out the possibility of really large life forms there; but would still expect them to be expect them to be extremely primitive All the best, Robert Clements <[EMAIL PROTECTED]> == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
>>>What in the world is a weta? Director Peter Jackson's Wellington-based SFX company. :-) Jayme Lynn Blaschke ___ *Cyclops in B Minor* by Jayme Lynn Blaschke now available from Mooncast Shadows http://www.exoticdeer.org/chapbook.html The Blaschke Home Realm http://www.vvm.com/~caius (u are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
>the reverse of this syndrome; & showed what happen when large >critters got trapped on small islands. Wrangell Island with its dwarf mammoths is another good example of this. Jayme Lynn Blaschke ___ *Cyclops in B Minor* by Jayme Lynn Blaschke now available from Mooncast Shadows http://www.exoticdeer.org/chapbook.html The Blaschke Home Realm http://www.vvm.com/~caius (u are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
In a message dated 12/8/2000 4:06:42 AM Alaskan Standard Time, [EMAIL PROTECTED] writes: << Come on over to Jason Perry's "Jupiter List" and "ISSDG" discussion groups and you can see Clements and I tearing at each other and questioning each other's ancestry on a regular basis. It's wonderful. >> Vodka and whiskey, whiskey and vodka... too much of a good thing is a bad thing. 'Tis best not to drink too deeply from the well, as it were. -- JHB == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
RE: On The Rise of Oxygen...
Thank you very much! > -Original Message- > From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of > Bruce Moomaw > Sent: 08 December 2000 15:44 > To: Icepick Europa Mailing List > Subject: Re: On The Rise of Oxygen... > > > > > -Original Message- > From: Evan James Dembskey <[EMAIL PROTECTED]> > To: [EMAIL PROTECTED] <[EMAIL PROTECTED]> > Date: Friday, December 08, 2000 5:27 AM > Subject: RE: On The Rise of Oxygen... > > > >Bruce, > > > > > >> Come on over to Jason Perry's "Jupiter List" and "ISSDG" discussion > groups > >> and you can see Clements and I tearing at each other and > questioning each > >> other's ancestry on a regular basis. It's wonderful. > > > > > > > >Would you be so kind as to point me in the right direction to > sub to these? > > > > > Sure: www.egroups.com/group/jupiter_list > www.egroups.com/group/ISSDG > > (You have to subscribe, which is both free and easy.) > Seriously, most of the discussion action that used to occur at the Europa > Icepick website seems to have moved over to these two sites -- simply > because there hasn't been much news specifically on Europa exploration in > recent months, and in any case it was obvious that a lot of the people > linked to the Icepick website were interested in more general > exploration of > the Solar System. > > Bruce > > == > You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] > Project information and list (un)subscribe info: http://klx.com/europa/ > == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
-Original Message- From: Evan James Dembskey <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Date: Friday, December 08, 2000 5:27 AM Subject: RE: On The Rise of Oxygen... >Bruce, > > >> Come on over to Jason Perry's "Jupiter List" and "ISSDG" discussion groups >> and you can see Clements and I tearing at each other and questioning each >> other's ancestry on a regular basis. It's wonderful. > > > >Would you be so kind as to point me in the right direction to sub to these? > Sure: www.egroups.com/group/jupiter_list www.egroups.com/group/ISSDG (You have to subscribe, which is both free and easy.) Seriously, most of the discussion action that used to occur at the Europa Icepick website seems to have moved over to these two sites -- simply because there hasn't been much news specifically on Europa exploration in recent months, and in any case it was obvious that a lot of the people linked to the Icepick website were interested in more general exploration of the Solar System. Bruce == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
-Original Message- From: Robert Clements <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Cc: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Date: Friday, December 08, 2000 1:43 AM Subject: Re: On The Rise of Oxygen... > >Bruce Moomaw wrote: >> >> While I didn't know that the huge dragonflies held on into the early >> Mesozoic, Clements' explanation has a big problem: why didn't the equally >> huge crawling bugs of the Carboniferous Era hold on? They didn't have the >> clumsy-flight disadvantage of those huge dragonflies -- there's no obvious >> competitive-evolutionary reason why we don't still have two-foot cockroaches >> and 6-foot millipedes around. It seems likely that the decline of the >> oxygen level in the early Mesozoic was indeed the key factor in nudging >> these horror-movie refugees into extinction. >> >> Of course, one qualification: there are still a few giant gadflies around. >> Witness Clements. >> >> Bruce Moomaw > >You're taking me way back into biomechanical studies i thought i forgot decades >ago; but there are disadvantages to being a large hard shelled bug of any kind. >One of the bigger is respiration; which is why the O2 rich periods of the >Palezoic suited our not-so-little frees to a t (or more precisely: 02); but in >the absence of competition capable of perhaps literally stomping these critters >out of existance, big bugs would still be around... qv, the weta in NZ; which i >think is one of the biggest land arthropods surviving; & which did survive in >the highly anomalous New Zealand paleoenvironment. > What in the world is a weta? More generally, in today's lower-oxygen environment, big bugs must be much more sluggish, which puts them at a severe disadvantage both in chasing prey and in surviving predation themselves. A few of them still hold on in very specialized ecological niches, but it still seems overwhelmingly likely that what wiped out almost all of them -- either directly or indirectly -- was that O2 loss. (Note, by the way, that almost all the surviving big arthropods are aquatic, simply because they don't have to carry their own weight around.) I just had a thought: Would the higher O2 level of the Permian mean that the worldwide fires set by an asteroid impact would be much more severe back then -- and could this possibly explain why the Permian extinction was so much more complete than the Cretaceous one? (It wouldn't directly explain why the Permian marine extinction was also worse; but maybe the increased smoke -- and the resultant natural "nuclear winter" effect -- would also have been more severe.) Bruce Moomaw == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
-Original Message- From: [EMAIL PROTECTED] <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Date: Friday, December 08, 2000 2:49 AM Subject: Re: On The Rise of Oxygen... > >I gotta say, Robert, reading your posts brought grim glee to my day. We >missed you, our giant gadfly! > >-- JHB Come on over to Jason Perry's "Jupiter List" and "ISSDG" discussion groups and you can see Clements and I tearing at each other and questioning each other's ancestry on a regular basis. It's wonderful. Bruce Moomaw == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
I gotta say, Robert, reading your posts brought grim glee to my day. We missed you, our giant gadfly! -- JHB == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
Bruce Moomaw wrote: > > While I didn't know that the huge dragonflies held on into the early > Mesozoic, Clements' explanation has a big problem: why didn't the equally > huge crawling bugs of the Carboniferous Era hold on? They didn't have the > clumsy-flight disadvantage of those huge dragonflies -- there's no obvious > competitive-evolutionary reason why we don't still have two-foot cockroaches > and 6-foot millipedes around. It seems likely that the decline of the > oxygen level in the early Mesozoic was indeed the key factor in nudging > these horror-movie refugees into extinction. > > Of course, one qualification: there are still a few giant gadflies around. > Witness Clements. > > Bruce Moomaw You're taking me way back into biomechanical studies i thought i forgot decades ago; but there are disadvantages to being a large hard shelled bug of any kind. One of the bigger is respiration; which is why the O2 rich periods of the Palezoic suited our not-so-little frees to a t (or more precisely: 02); but in the absence of competition capable of perhaps literally stomping these critters out of existance, big bugs would still be around... qv, the weta in NZ; which i think is one of the biggest land arthropods surviving; & which did survive in the highly anomalous New Zealand paleoenvironment. All the best, Robert Clements <[EMAIL PROTECTED]> == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
-Original Message- From: Robert Clements <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Cc: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Date: Thursday, December 07, 2000 11:54 PM Subject: Re: On The Rise of Oxygen... > >[EMAIL PROTECTED] wrote: > >> >> f) here's a somewhat unrelated question: what did Dinosaurs breath? >> Could the air have been thicker then, perhaps with somewhat exotic chemistry >> to it? How else to explain 2' dragonflies, and 80' brachiosaurs... 'heavier' >> air might explain how a 2' dragonfly still could acheive loft, and how >> dinosaurs could supply enough oxygen through those tiny heads to feed such a >> massive body. >> >> Any ideas or critiques out there? >> >> -- JHB, the gadfly > >No significant difference in the oxygen content of the atmosphere following the >Permian extinction (ie, the Mesozoic; which became the age of the dinosauria); >although the planet was somewhat warmer... even in antarctic Australia, many >species survived months of total darkness with little difficulty. Although the 2' >dragonflies may have first appeared during a period with more user friendly >atmospheric conditions than currently, they were still alround in the early >Mesozoic, when the conditions were much more contemporary. > >The real explanation for the 2' dragonflies & larger sauropods such as >Seismosaurus or Argentiosaurus (both of which make the brachiosaurs look like >anorexic midgets) is much simpler. There's a basic rule in biology that says: all >other things being equal, its better to be big than little. > >Nowadays, all other things are not equal - mostly due to human greed - & being >large is a major disadvantage; but when the big dragonflies were around, they >owned the skies; & as a result could survive quite comfortably despite their >being almost certainly a fairly awkward flyer. When a new & more effective design >for flight - the pterosaurs - appeared, the dragonflies quickly vanished; & the >ptersoaurs grew enormous (Queztalcoatlsaurus had a bigger wingspan than a cricket >pitch (21m)). Pterosaurs were also not ideal flyers, though; & when good bird >designs took to the air in the Creataceous, the flying reptiles didn't last very >long; & were probably pushing extinction long before the Chicxulub impact event. While I didn't know that the huge dragonflies held on into the early Mesozoic, Clements' explanation has a big problem: why didn't the equally huge crawling bugs of the Carboniferous Era hold on? They didn't have the clumsy-flight disadvantage of those huge dragonflies -- there's no obvious competitive-evolutionary reason why we don't still have two-foot cockroaches and 6-foot millipedes around. It seems likely that the decline of the oxygen level in the early Mesozoic was indeed the key factor in nudging these horror-movie refugees into extinction. Of course, one qualification: there are still a few giant gadflies around. Witness Clements. Bruce Moomaw == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
Re: On The Rise of Oxygen...
[EMAIL PROTECTED] wrote: > > f) here's a somewhat unrelated question: what did Dinosaurs breath? > Could the air have been thicker then, perhaps with somewhat exotic chemistry > to it? How else to explain 2' dragonflies, and 80' brachiosaurs... 'heavier' > air might explain how a 2' dragonfly still could acheive loft, and how > dinosaurs could supply enough oxygen through those tiny heads to feed such a > massive body. > > Any ideas or critiques out there? > > -- JHB, the gadfly No significant difference in the oxygen content of the atmosphere following the Permian extinction (ie, the Mesozoic; which became the age of the dinosauria); although the planet was somewhat warmer... even in antarctic Australia, many species survived months of total darkness with little difficulty. Although the 2' dragonflies may have first appeared during a period with more user friendly atmospheric conditions than currently, they were still alround in the early Mesozoic, when the conditions were much more contemporary. The real explanation for the 2' dragonflies & larger sauropods such as Seismosaurus or Argentiosaurus (both of which make the brachiosaurs look like anorexic midgets) is much simpler. There's a basic rule in biology that says: all other things being equal, its better to be big than little. Nowadays, all other things are not equal - mostly due to human greed - & being large is a major disadvantage; but when the big dragonflies were around, they owned the skies; & as a result could survive quite comfortably despite their being almost certainly a fairly awkward flyer. When a new & more effective design for flight - the pterosaurs - appeared, the dragonflies quickly vanished; & the ptersoaurs grew enormous (Queztalcoatlsaurus had a bigger wingspan than a cricket pitch (21m)). Pterosaurs were also not ideal flyers, though; & when good bird designs took to the air in the Creataceous, the flying reptiles didn't last very long; & were probably pushing extinction long before the Chicxulub impact event. We have an even better case study with the sauropods; which followed two different lines of destiny in the late Cretaceous. In either line of evolution, lacking an internal means for temperature control (unlike mammals or birds, say; which have to eat huge amounts of feed to simply keep their body temperatures up) meant that being large had considerable advantages (ie, the critter had a good volume/surface area ratio; so could use waste heat from metabolism effectively as a body heat) without the disadvantages of inevitably eating themselves out of house & home faster than they could heat up, which would probably be the case with really sauropodian mammals. (There is a mythology than many of even more dinosaurs are warm blooded. This is based on some very strange writings by Bob Bakker; which often makes even the experts wonder whether the understands the difference between having a high body temperature (which can be achieved by various mechanisms, including sheer size) & having an internally regulated body temperature such as we mammals do. It's entirely possible that some bird-related - or bird-descended, if the controversial Birds Came First theory is correct (& BCF actually fits the current evidence better than the conventional version) - may have had an ability to artificially inflate their body temperatures by eating huge amounts of food; but there's no good evidence to support even that. (& bear in mind: if an animal is large, it _doesn't_ need to have an internally regulated body temperature to be warm blooded & therefore active... esp. in an environment which was already relatively warm. (Bear in mind, too, that some of the brontotheres of the mid Cainozoic were pretty weight competitive with at least the smaller sauropods. No doubt the brontotheres were something less than wildly active; but this shows that sauropodian mammals - while probably less likely than their dinosaurian counterparts - were not completely impossible) An extinct evention - possibly asteroid related - at the end of the Jurassic had hammered all the large critters; & those sauropods which survived in what is now China, Siberia & North America struggled in competition with new fangled plant eaters such as the ceratopsians (triceratops being the most famous of this breed) & hadrosaurs & so were much smaller than their Jurassic antecedents; but in Patagonia & Africa, the bigger is better syndrome continued unchecked & some really big sauropods like Seismo & Argentino shook the Earth. What this tells us clearly is that it _wasn't_ a change in environmental conditions which doomed the giant sauropod line: it was competition (in Siberia, China & NAmerica) & finally the Chicxulub impact (everywhere else) which did 'em in. Another good eg of this phenomenom at work is amboreiser, the enormous (& i do mean enormous: some where the size of small bears) rat of greater Anguilla. No unusual atmospheric s
Re: [ISSDG] Re: On The Rise of Oxygen...
In a message dated 12/5/2000 4:38:40 AM Alaskan Standard Time, [EMAIL PROTECTED] writes: << The consensus now is that the Carboniferous and Pennsylvanian eras of the Paleozoic did indeed feature much higher atmospheric oxygen levels, and that this allowed insects to overcome the burden of their inefficient respiratory systems and evolve to huge size. As I understand it, though, the O2 levels were a lot closer to present-day levels during the Mesozoic era, and so had relatively little to do with the huge size of the dinosaurs (although a minority of scientists think they may have been higher during that era too). The fact that dinosaurs evolved to much bigger sizes than mammals may have been due to the fact that -- because they were cold-blooded -- they got more of an advantage out of having huge unwieldly bodies than manmmals do, because those huge bodies would make it easier for them to control their internal temperatures. >> Ah... well, it's been my understanding that there's a growing concept among dinosaur scientists that dinosaurs were not quite cold blooded... that they may have been similar to birds, etc, with very high metabolisms. Some dinosaurs, it's speculated, actually had feathers to help regulate. Feathers, as you know, are even more efficient than fur for heat retention. Or, maybe dinosaurs had blubber? Up here in Alaska, various species of freshwater fish actually have a blood protein that acts as an anti-freeze; in winter, the fish get torpid, but they don't die. Consider also, cryolofosaur, a dinosaur recently found in Antarctica. Antartica has supposedly always been fairly cold -- although at the time of cryolofosaur, it may have been similar to Alaska. How about ichthyosaurs? If they could actually dive 500 meters down, they must have had some amazing body chemistry going on, because they were air breathers. They had to regulate their body temperature in water (water is especially chilling, because it moves heat away from a body). Imagine the temperature spike going from 500 meters down to the temperature on the surface... yet ichthyosaurs lasted 100 million+ years. I just can't buy the 'cold blooded lizard' routine. It has a hole big enough to drive a train through it. On the other hand, if dinosaurs were semi-warm blooded, then a little chill would have really hurt them, because with a bigger body, it would take longer to heat it up after a temperature drop, than a smaller, furry mammal. I still want to read a GOOD explanation for a whale sized brachiosaur moving around, while the biggest mammal that I know of was a titanothere, only 30 tons or so. Someone's got some 'splaining to do. However, since this is an astronomy posting board, I'll have to move back to at least a modicum of relation to that. I suppose that it could be pointed out that exobiota may be possible in all sorts of environments we haven't even dreamed of, trapped in our contemporary blinders as we are. -- JHB == You are subscribed to the Europa Icepick mailing list: [EMAIL PROTECTED] Project information and list (un)subscribe info: http://klx.com/europa/
[ISSDG] Re: On The Rise of Oxygen...
-Original Message- From: [EMAIL PROTECTED] <[EMAIL PROTECTED]> To: [EMAIL PROTECTED] <[EMAIL PROTECTED]> Date: Tuesday, December 05, 2000 1:14 AM Subject: On The Rise of Oxygen... >I have some questions regarding the oxygen boom referred to in the last posting... > >1) presuming that glaciation was involved, could the following help explain it? > a) glaciation would seem to be a downward spiral; that is, a lot of ice >chills the ocean currents, it chills the air, it dries the air, and snow/ice >has a high albedo -- effectively reflecting a lot of potentially warming >sunlight. You'd think that once an Ice Age starts, it would continue into >glacier lock. However... > b) glaciers are heavy; a mile thick ice sheet is so heavy that it >actually compresses the crustal rock into the mantle. Evidence is found in >Sweden, where the land is still rising after the last Ice Age (during >which, >Sweden was completely covered with 1 mile of ice). > c) consider: if a mile sheet of ice covered the land, wouldn't that >weight eventually 'squirt' the underlying magma somewhere else? Thus, with >enough glaciation, eventually an automatic reverse might trigger, in that >glaciation may lead to an upwelling of volcanism, which blasts CO2 into the >atmosphere... causing a greenhouse effect, and reversing the global cooling >of the glaciation. > Actually, the theory has been that those Precambrian super-glaciated ages sowed the seeds of their own destruction more directly -- by freezing over the oceans and thus sealing off much of the liquid water on Earth's surface from direct exposure to the air. The volcanoes on land continued to belch CO2 into the air -- but now there was no weathering process (which requires liquid water) to make the CO2 react with Earth's silicate rocks and turn into carbonates. So the CO2 built up in the atmosphere, until the increased greenhouse warming from it finally caused enough ice to melt in the equatorial regions that the Earth's total albedo darkened to the point that the former "runaway glaciation" was reversed by a "runaway deglaciation" (in which the fact that the glaciers shrank and Earth darkened in color warmed it up and made the glaciers shrink still faster). This runaway deglaciation, in fact, would have occurred so fast that the glaciers would all have melted and Earth returned to normal temperature BEFORE the resultant increase in carbonate weathering could mop up all the CO2. So there would then have been a period in which Earth's temperature was far ABOVE normal thanks to all that remaining CO2 -- a torrid greenhouse characterized by violent planetwide rains of seltzer water (and sulfuric acid, since SO2 gas from the volcanoes would also have built up in the air during the glacial period. This era of torrid "acid rain" would then have pretty quickly turned all that excess CO2 and SO2 back into big carbonate and sulfate layers -- which do in fact exist in the Precambrian rock strata of that time, and constitute one of the biggest pieces of evidence that something weird happened during those periods. The big question, then is: why did Earth's "carbonate weathering thermostat" -- which normally keeps the planet's temperature pretty stable by increasing the rate at which volcano-emitted atmospheric CO2 is turned into carbonates if Earth starts to warm up, and the reverse if Earth starts to cool down -- malfunction so seriously in those eras in the first place? Why did it ever let Earth get cold enough, and thus ice over enough, to cause that runaway glaciation in the first place? There's quite a lot of speculation on this -- the leading theory has been that continental drift happened to herd all of Earth's continents together into a single equatorial super-continent during those eras, reducing the temperatures of the polar regions and also increasing the total length of the rivers and streams running across the land surfaces into the sea (which would have increased the carbonate weathering rate and thus "turned down" the carbonate thermostat). Kasting was pushing that view at the Ames Astrobiology Conference last April, but now he seems to have come up with a new theory. >d) during the Pleistocene (Ice Ages) the glaciers advanced and receded >half a dozen times in 2 million years, causing all sorts of evolutionary >changes to propel forward, including our own. A glacier age may have thus >been intimately linked to the paleozoic boom, no? > There has indeed been quite a lot of speculation that the super-glaciation eras may have had something to do with the Cambrian evolutionary explosion, by "stirring up the ecological pot" and allowing new life forms to gain a foothold in the temporarily decimated post-glacial world -- but nobody really knows. > e) early biota are anaerobic, and poisoned by oxygen. A mutation which >could actually survive despite (and eventually because of) a massive influx >of oxygen into the air would h
