Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!lll-crg!rutgers!clyde!cbatt!ihnp4!inuxc!pur-ee!j.cc.purdue.edu!i.cc.purdue.edu!ahv From: ahv@i.cc.purdue.edu (Jer Bear) Newsgroups: sci.misc Subject: Re: alternative to plate tectonics Message-ID: <1686@i.cc.purdue.edu> Date: Fri, 5-Dec-86 22:13:21 EST Article-I.D.: i.1686 Posted: Fri Dec 5 22:13:21 1986 Date-Received: Sun, 7-Dec-86 13:56:34 EST References: <531@weitek.UUCP> Reply-To: ahv@i.cc.purdue.edu.UUCP (Jer Bear) Organization: The National Create-A-Data Corp Lines: 100 >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