mae@weitek.UUCP (Mike Ekberg) (12/03/86)
About ten years ago, while I was in college, I read a book that presented a theory to explain many of the phenomenon used to back up the theory of plate tectonics. The theory went something like this... The earth consists of a large gob of semi-liquid stuff(mantle) that is coated with an extremly thin shell of hardened goop, ie crust. Occasionally, for unknown reasons, the thin shell 'slips' over the surface of the semi-liquid stuff. After a while, the shell movement reaches some sort of equilibrium(sort of like Punctuated Revolution? :-} ). This theory 'explains' the following phenomenon: 1. magnetic reversals - since the magnetic pole is in the mantle, when the crust shifts relative to the mantle, the apparent direction of the earths magnetic field shifts. 2. sea floor expansion - since the earth is not a perfect sphere, when the crust shifts, cracks open as the crust gets stretched of the bulgy parts. Stuff leakes out from the interior. 3. weird fossil records - the author sited examples of fossils of tropical plants in Siberia. Siberia used to be on the equator. Is there anything to this theory or is it totally from left field? BTW, according to the Grab Bag column in the S. F. Examiner, the crust is much thinner relative to the inside then an egg shell is to the egg.
myers@hobiecat.Caltech.Edu (Bob Myers) (12/04/86)
In article <531@weitek.UUCP> mae@weitek.UUCP (Mike Ekberg) writes: >About ten years ago, while I was in college, I read a book that presented >a theory to explain many of the phenomenon used to back up the theory of >plate tectonics. > >The theory went something like this... > >The earth consists of a large gob of semi-liquid stuff(mantle) that is coated >with an extremly thin shell of hardened goop, ie crust. Occasionally, >for unknown reasons, the thin shell 'slips' over the surface of the >semi-liquid stuff. After a while, the shell movement reaches some sort >of equilibrium(sort of like Punctuated Revolution? :-} ). > >This theory 'explains' the following phenomenon: > >1. magnetic reversals - since the magnetic pole is in the mantle, > when the crust shifts relative to the > mantle, the apparent direction of the > earths magnetic field shifts. It doesn't explain why the field shifts direction 180 degrees. Not unless you really believe that the entire crust rotates exactly 180 degrees around some equatorial pole. I find that incredibly hard to believe. >2. sea floor expansion - since the earth is not a perfect sphere, > when the crust shifts, cracks open as the > crust gets stretched of the bulgy parts. > Stuff leakes out from the interior. All right, I guess you need some explaination of plate tectonics (and the evidence for it.) Okay, Seafloor spreading: Around the world there are ridges in the ocean, called mid-ocean ridges. There is a lot of volcanism there. On both sides of these ridges you can find magnetic reversal patterns (symmetric) which correspond to the dated patterns of magnetic reversal on the continents. Now, these patterns had to be imprinted in the rock when it was very hot, above a temperature called the curie temperature (can't remember off hand how hot that is, but it's a lot hotter than is normally found.) Basically it was laid in when the rock solidified. These are fairly continuous patterns dating back over 170 million years, with reversals every million years or so (sometimes much more often). The spreading is at a relatively continuous rate, at least at this time scale. Any theory must account for this. Somehow I find it much easier to believe slow continuous spreading than occaisional massive shifts of the entire crust, which simulate slow spreading sooo well. >3. weird fossil records - the author sited examples of fossils of > tropical plants in Siberia. Siberia used > to be on the equator. According to plate tectonics, the continents are drifting. They move slowly, but they do move. Siberia was tropical once, according to plate tectonics. >Is there anything to this theory or is it totally from left field? I haven't even mentioned that seismic evidence supports this stuff, and that spreading is occuring today (measurably). To say nothing of subduction zones (ocean trenches, where ocean crust goes back down into the mantle to be recycled). >BTW, according to the Grab Bag column in the S. F. Examiner, the crust is >much thinner relative to the inside then an egg shell is to the egg. Well, I don't know how thin an eggshell is, but that's definitely true. The oceanic crust is about 7km thick, and the continental crust is about 35km thick. The Earth is 6370km in radius, so using continental crust, the crust is 0.55% of the Earth's radius. If an egg is 3cm in radius (a pretty large egg), the equivalent thickness of the crust is 0.16mm. That's a pretty thin shell. Bob Myers
myers@hobiecat.Caltech.Edu (Bob Myers) (12/04/86)
A slightly better alternative than the previous one is the Expanding Earth hypothesis. This explains seafloor spreading by expansion of the Earth's interior, causing the crust to stretch. Not that I believe it.... In any case, I did a literature review of this idea a couple years ago. It would be easy to e-mail a copy to anyone who requests it. Bob Myers
bob@uhmanoa.UUCP (Bob Cunningham) (12/04/86)
> A slightly better alternative than the previous one is the > Expanding Earth hypothesis. This explains seafloor spreading by > expansion of the Earth's interior, causing the crust to stretch. Unfortunately, the Expanding Earth hypothesis ignores several decades of research involving hot spots, subduction zones, active margins, island arcs, and passive margins. The critical evidence which lead to the clear identification of the deep oceanic trenches (or, more precisely the "Benioff zones" associated with them) with sinking tongues of oceanic lithosphere came from work done on the Tonga Trench in the mid 1960s using the World-Wide Standardized Seismograph Network. Subduction was clearly shown. Since then, the same essential picture has been seen at the other major trenches. Also, very careful measurements of plate movements have been made, using not only paleological and magnetic analyses, but also using careful surveying techniques, including measurements using satellite navigation techniques. Turns out that the plates are definitely moving around at relatively rapid speeds (well, rapidly geologically speaking) of the order of centimeters per year. One of the problems has been trying to determine what to use as a global reference that could be considered relatively static (sort of a geological version of "relativity" :-). The current popular static reference is the means of the global "hot spots" which don't seem to move too much relative to each other. To see the effects of a plate (the Pacific plate) moving over a "hot spot", get out your favorite globe or world map and look at the Hawaiian islands. The youngest island is Hawaii at the southern end of the chain (actually, it's the undersea volcano Loihi just southeast of Hawaii). The rest of the chain of islands are progressively older as they trend northwest for 1,000 miles or so. If you have a map or chart which details undersea features, you can follow the remains of even older islands that are known as the "Emperor Seamounts" for considerably further towards the northwest. [Congratulations if you see a change of direction, the Pacific plate hasn't always been moving in exactly the same way.] -- Bob Cunningham bob@hig.hawaii.edu
jbuck@epimass.UUCP (Joe Buck) (12/04/86)
In article <1273@cit-vax.Caltech.Edu> myers@hobiecat.UUCP (Bob Myers) writes: >A slightly better alternative than the previous one is the >Expanding Earth hypothesis. This explains seafloor spreading by >expansion of the Earth's interior, causing the crust to stretch. Using very long baseline interferometry, one can actually measure the continents' motion (it amounts to an inch or so a year in most cases). The results support plate tectonics, not an expanding earth (some continents are getting closer together). I have a friend at NASA-Goddard who is involved in this work. -- - Joe Buck {hplabs,ihnp4,sun}!oliveb!epimass!jbuck HASA (A,S) Entropic Processing, Inc., Cupertino, California
bob@uhmanoa.UUCP (Bob Cunningham) (12/05/86)
For a description of some of the VLB interferometry work, see the Carter & Robertson article in the Nov 1986 Scientific American. -- Bob Cunningham bob@hig.hawaii.edu
ma_jpb@bath63.ux63.bath.ac.uk (Bennett) (12/06/86)
There is a problem with tectonic plate theory and continental drift due to the conservation of energy. Consider the theory that the Himalayas are caused by the Indian plate hitting the Asiatic plate. A substantial amount of potential energy is generated in raising the Himalayas, which has presumably come from the kinetic energy of the Indian plate. Given we can work out the kinetic energy of the plate, we can calculate the height of the mountains this would raise if converted to potential energy with 100% efficiency. Although the Indian plate is large it moves exceedingly slowly (a few centimetres a year at most). Calculation would suggest that within an order of magnitude the Himalayas should be one millimetre high. Observation refutes this. At least in this case continental drift is not a good model. This is a well documented objection, and has led to the foundation of the "Stop Continental Drift Society" (of which I hasten to add I am not a member). If there is enough demand I can dig out the references to papers that discuss this theory. J.P. Bennett University of Bath England BA2 7AY +44 225 826826
ahv@i.cc.purdue.edu (Jer Bear) (12/06/86)
>About ten years ago, while I was in college, I read a book that presented >a theory to explain many of the phenomenon used to back up the theory of >plate tectonics. >The theory went something like this... > >The earth consists of a large gob of semi-liquid stuff(mantle) that is coated The mantle is very much solid, in fact it is more dense than most any of the rocks seen on the surface. The core of the earth is partial molten (the center part is not however). >with an extremely thin shell of hardened goop, ie crust. Occasionally, Basically correct. >for unknown reasons, the thin shell 'slips' over the surface of the >semi-liquid stuff. After a while, the shell movement reaches some sort >of equilibrium(sort of like Punctuated Revolution? :-} ). > This 'thin shell' is constantly moving at a slow rate, on what is known as the mid-atlantic ridge about 2 cm per year. Now this may not seem like a lot but for geology this is very rapid movement. >This theory 'explains' the following phenomenon: >1. magnetic reversals - since the magnetic pole is in the mantle, > when the crust shifts relative to the > mantle, the apparent direction of the > earths magnetic field shifts. Magnetic reversals are believed to be caused by convection currents in the core of the earth, which acts as kind of a magnet. Some directional changes are caused by the movement of the crust over the mantle also, but only in the crust, not the rest of the earth. >2. sea floor expansion - since the earth is not a perfect sphere, > when the crust shifts, cracks open as the > crust gets stretched of the bulgy parts. > Stuff leakes out from the interior. This happens in that were places like the mid-atlantic ridge occur the drop in pressure caused by the crust being stretched causes the rock in the mantle to melt, and because this melted rock is lighter than what surrounds it, it works its way to the surface and creates the 'stuff that leaks out'. This stuff (melt) also hardens to form new crustal material because not near all of it reaches the surface. The distance that this melt must travel is about 10 km. >3. weird fossil records - the author sited examples of fossils of > tropical plants in Siberia. Siberia used > to be on the equator. Using the fact that the crustal 'plates' have moved in the past as well as they are currently moving also produces changing environments. Indiana, for example, during one period in geologic time also was near the equator. Coral reefs, abundant limestone (Indiana University and many of the buildings in Washington D.C. were made of one very pure type of limestone,) and coal were all formed under tropical conditions. The northward movement of the North American plate has brought cooler weather to this once Bahama-type environment. Traces of glaciers can be found in very dry areas of Africa. >BTW, according to the Grab Bag column in the S. F. Examiner, the crust is >much thinner relative to the inside then an egg shell is to the egg. It is. That is why it is so difficult to study the mantle and core, because the crust, even though it is relatively thin, is on land up to 30 km thick, and in the oceans about 6-10 km thick. A project known as the Deep Sea Drilling Project has drilled a hole 1.5 km deep, barely scratching the surface. The mantle and core are studied using siesmic procedures using such things as earthquakes and planned and controlled explosions. This subject of plate tectonics touches all areas of geology to some degree. I am a geology under- graduate here at Purdue University and am currently taking a course about this very subject. All the current literature I am familier with is very technical. This theory has been greatly refined since it was first proposed. Perhaps another geologist out there can come up with a good non-technical book on the subject. Any protests or other questions can be sent to this account. Ellen Meadows Disclaimer : The views stated herein are the views of the author and in no way should be connected to the organization to which I or to me for that matter. -- In Real Life: Jerry L. Bloomfield USENET: {seismo, decvax, ucbvax, ihnp4}!pur-ee!h.cc!ahv BITNET: BLOO@PURCCVM
myers@hobiecat.Caltech.Edu (Bob Myers) (12/07/86)
In article <648@bath63.ux63.bath.ac.uk> (Bennett) writes: > >There is a problem with tectonic plate theory and continental drift due to the >conservation of energy. Consider the theory that the Himalayas are caused by >the Indian plate hitting the Asiatic plate. A substantial amount of potential >energy is generated in raising the Himalayas, which has presumably come from >the kinetic energy of the Indian plate. Given we can work out the kinetic >energy of the plate, we can calculate the height of the mountains this would >raise if converted to potential energy with 100% efficiency. Although the >Indian plate is large it moves exceedingly slowly (a few centimetres a year at >most). Calculation would suggest that within an order of magnitude the >Himalayas should be one millimetre high. Observation refutes this. At least in >this case continental drift is not a good model. BULLSHIT BULLSHIT BULLSHIT If I push a cart with my hand, does it get all its energy from the kinetic energy of my hand??? It gets its energy from what drives the motion of my hand. Same for plates. I have seen a couple of proposals for driving energy for plate motion. Ex.: Potential energy as the plate moves down from the mid-ocean ridge crest (where it is formed) and then gets subducted into the mantle. It has been proposed that the subducting end falling into the mantle (it is heavier, mostly because it's colder) creates the plate motion by pulling the plate down. Ex.: Mantle convection. Upwelling at ridge crests, downwelling near subduction zones, energy driven by internal heat of the Earth. ridge crest subduction ->>>>>>>>>>>> zone ^ \/ ^ \/ ^ \/ ^ \/ <<<<<<<<<<<<<< Bob Myers
larry@jc3b21.UUCP (Lawrence F. Strickland) (12/07/86)
Just recently on Public TV, there was a show that mentioned plate tectonics,
sea-floor spreading and the like. They made one very interesting statement
that I'm having a lot of trouble verifying. According to Wegner's hypothesis,
there was once a large super-continent (Pan-gaea) that split up to form the
later continents. MUCH evidence supports this. Also supported is the fact
that the current continent shapes (plus or minus a few buldges) are very
similar to what the were when Pan-gaea broke up.
Now the show I saw contended that for North America, at least, the continent
was built up from deposition on an originally smaller continent based in
southern Canada. They called it the Canadian shelf or something like that.
They also noted that this rock PRE-DATED the formation of Pan-Gaea!
Try as I might, I can't find any books or other sources that either confirm or
deny this. Most go back to Pan-gaea and talk about the break up and the sea-
floor spreading and subduction that has taken place since then, but nothing
that would indicate shapes of continents prior to the formation of Pan-gaea.
Was this just a flight of fancy of the author of the show? Are there any
theories on continents prior to Pan-gaea? Where can one find this stuff??
-----Larry
--
-----Lawrence F. Strickland (larry@jc3b21) Dept. of Engineering Technology
St. Petersburg Jr. College
Phone: +1 813 341 4705 P.O. Box 13489
UUCP: ...akgua!usfvax2!jc3b21!larry St. Petersburg, FL 33733ethan@utastro.UUCP (Ethan Vishniac) (12/09/86)
In article <648@bath63.ux63.bath.ac.uk>, ma_jpb@bath63.ux63.bath.ac.uk (Bennett) writes: > > There is a problem with tectonic plate theory and continental drift due to the > conservation of energy. Consider the theory that the Himalayas are caused by > the Indian plate hitting the Asiatic plate. A substantial amount of potential > energy is generated in raising the Himalayas, which has presumably come from > the kinetic energy of the Indian plate. Given we can work out the kinetic > energy of the plate, we can calculate the height of the mountains this would > raise if converted to potential energy with 100% efficiency. Although the > Indian plate is large it moves exceedingly slowly (a few centimetres a year at > most). Calculation would suggest that within an order of magnitude the > Himalayas should be one millimetre high. Observation refutes this. At least in > this case continental drift is not a good model. > I am *not* a geologist. Perhaps that is why I can't understand this argument. I always thought that continental drift was supposed to be driven by the interaction between the crust and convective currents from deep within the Earth. If this were not so then continental motion would never have started and if started would stop quickly. After all the motions of the plates are highly dissipative. The energetics must work like this: radioactive decay of heavy atoms - > thermal energy of core -> convective currents -> deformations of crust and other dissipative effects. Mr. Bennett's argument can allow us to calculate the rate at which energy is being transferred from internal convective currents into the kinetic energy of the Indian subcontinent. Unless I'm completely mistaken (rarely out of the question :-) ) it tells us nothing about the validity of plate tectonics. -- "More Astronomy Ethan Vishniac Less Sodomy" {charm,ut-sally,ut-ngp,noao}!utastro!ethan - from a poster seen ethan@astro.AS.UTEXAS.EDU at an airport Department of Astronomy University of Texas
dant@tekla.UUCP (12/10/86)
In article <648@bath63.ux63.bath.ac.uk> ma_jpb@ux63.bath.ac.uk (Bennett) writes: > >There is a problem with tectonic plate theory and continental drift due to the >conservation of energy. Consider the theory that the Himalayas are caused by >the Indian plate hitting the Asiatic plate. A substantial amount of potential >energy is generated in raising the Himalayas, which has presumably come from >the kinetic energy of the Indian plate. Given we can work out the kinetic >energy of the plate, we can calculate the height of the mountains this would >raise if converted to potential energy with 100% efficiency. Although the >Indian plate is large it moves exceedingly slowly (a few centimetres a year at >most). Calculation would suggest that within an order of magnitude the >Himalayas should be one millimetre high. Observation refutes this. At least in >this case continental drift is not a good model. Consider the following thought experiment: Take 2 identical cars and place them nose to nose. Rig the accelerators of both so that you can give equal acceleration to each. Now slowly increase the accelerations of the two cars. Assuming that there is no slippage of the wheels, the cars will remain motionless. That is until the bumpers start to crumple. If I remember my freshman physics, this state is called static equilibrium. The velocity of the cars (except for that allowed by the crumpling bumpers) is zero. Thus, their kinetic energy is also zero (or very close to it, the bumpers again). However, the force produced by each car is not zero. This is what is producing the crumpled bumpers (and the crumpled landscape i.e. Himalayas). So, what does kinetic energy have to do with it? >This is a well documented objection, and has led to the foundation of the "Stop >Continental Drift Society". Have the members of this Society taken freshman physics? Dan Tilque dant@tekla.tek.com Hey! Who left my Cosmic Holographic Recorder on replay?
dmu@lcuxlm.UUCP (12/10/86)
In article <648@bath63.ux63.bath.ac.uk>, ma_jpb@bath63.ux63.bath.ac.uk (Bennett) writes: > > There is a problem with tectonic plate theory and continental drift due to the > conservation of energy. Consider the theory that the Himalayas are caused by > the Indian plate hitting the Asiatic plate. A substantial amount of potential > energy is generated in raising the Himalayas, which has presumably come from > the kinetic energy of the Indian plate. Given we can work out the kinetic > energy of the plate, we can calculate the height of the mountains this would > raise if converted to potential energy with 100% efficiency. Although the > Indian plate is large it moves exceedingly slowly (a few centimetres a year at > most). Calculation would suggest that within an order of magnitude the > Himalayas should be one millimetre high.... True, but do we know the velocity of the Indian Plate 10 or 20 million years ago? Remember that once most of the kinetic energy of an object has been turned into potential energy, the object tends to be moving slowly, in comparison. Has anyone investigated this line? Doug Murphy AT&T-Bell Laboratories Liberty Corner, NJ {lcuxlm!dmu}
cipher@mmm.UUCP (Andre Guirard) (12/11/86)
>In article <648@bath63.ux63.bath.ac.uk>, ma_jpb@bath63.ux63.bath.ac.uk (Bennett) writes: > > There is a problem with tectonic plate theory and continental drift due to the > conservation of energy. Consider the theory that the Himalayas are caused by > the Indian plate hitting the Asiatic plate... Although the > Indian plate is large it moves exceedingly slowly... > Calculation would suggest that within an order of magnitude the > Himalayas should be one millimetre high.... This would indeed be a serious problem if the proposed mechanism causing continental drift was that the plates have leftover momentum from some past disaster and are bouncing off each other like billiard balls. It becomes evident with only a little thought that that would be a silly assertion, since the mantle is much thicker than lemon custard, and would slow them to a stop in no time (geologically speaking). In fact, I believe the theory goes that the plates are moved by convection currents in the chewy liquid center of the Earth, these currents being caused by heat generated by the decay of radioactive elements. There's a _lot_ more energy than just the momentum of the crustal plates involved. -- /'C`\ TWALG ASHALC RITMOHF. Andre Guirard ( o_o ) Botoj de timeco )) _ (( AWSWG SWVVG BWSWBSWH! ihnp4!mmm!cipher /// \\\
pamp@bcsaic.UUCP (Wagener) (12/12/86)
In article <777@jc3b21.UUCP> larry@jc3b21.UUCP (Lawrence F. Strickland) writes: > >Just recently on Public TV, there was a show that mentioned plate tectonics, >sea-floor spreading and the like. They made one very interesting statement >that I'm having a lot of trouble verifying. According to Wegner's hypothesis, >there was once a large super-continent (Pan-gaea) that split up to form the >later continents. MUCH evidence supports this. Also supported is the fact >that the current continent shapes (plus or minus a few buldges) are very >similar to what the were when Pan-gaea broke up. > >Now the show I saw contended that for North America, at least, the continent >was built up from deposition on an originally smaller continent based in >southern Canada. They called it the Canadian shelf or something like that. >They also noted that this rock PRE-DATED the formation of Pan-Gaea! > >Try as I might, I can't find any books or other sources that either confirm or >deny this. Most go back to Pan-gaea and talk about the break up and the sea- >floor spreading and subduction that has taken place since then, but nothing >that would indicate shapes of continents prior to the formation of Pan-gaea. > >Was this just a flight of fancy of the author of the show? Are there any >theories on continents prior to Pan-gaea? Where can one find this stuff?? > No, it wasn't a flight of fancy. What was being discussed was the theories of micro-plate accreation. This is work that has come out of the NW US and Western Canada studies back around 1978-1983. Most of the discussions have been going on in the geology technical journals. I don't have the references here at work, but I know that Dr.Charles A. Ross did some work in paleontology that discussed this theory and gave some supporting evidence. Other authors to look up are Zvi Ben-Avraham, Alan Cox, Amos Nur, and especially Davey Jones,Norman Silberling, and John Hillhouse (USGS). You would probably want to look up information on Wrangellia and allochthonous terranes. I do have one popular article on the subject. Overbye,Dennis, 1983, The Jigsaw Earth,Discover,april,n.4v.4,p.86-91. This gives a good description of what was covered in the tv show. Hope this helps. Pam Pincha-Wagener