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Author | Topic: Geologic Column | |||||||||||||||||||||||||||||||||
RAZD Member (Idle past 1665 days) Posts: 20714 From: the other end of the sidewalk Joined: |
originally Message 371
Hi Peg,
thankyou for the information Radz, ... You're welcome.
... I am not denying the existence or validity of the geologic column. I can clearly see that the oldest layers are on the bottom and accept that 100%. Is there any place on earth where the column exists in its entirety? That depends on how you look at it. The "column" is complete in every location - it has all the layers for that location. If we are looking for one location that has all the layers, then the "column" is the earth. Each new layer wraps around the previous layer, taking the shape of the previous layer/s as its base, and builds onto it. It also depends on what you call a layer. There is a layer called the iridium layer that covers a large proportion of the earth, and is the evidence of the meteor strike that hit the Yucatan Peninsula 65 million years ago - it has a distinctive level of iridium that is characteristic of meteors, hence it can be identified. This layer does not exist where it has been eroded away (such as where Tiktaalik was discovered), but it covers many different formations that are discontinuous layers, and it in turn is covered by many discontinuous layers. There are similar layers that contain volcanic ash, which covers a much wider area than lava, and in some cases can be found world wide.
Is there any place on earth where the column exists in its entirety? This is where the fun (for geologists) comes in. Some layers are necessarily local - volcanic lava flows do not cover the earth, but every one of them covers part of the earth, over older formations, so you may have several different sources providing material that cover different parts of other layers. Rather obviously you are not going to have lava flows from Oahu island in Connecticut, nor are you likely to find a sedimentary deposit from the Connecticut river on one of the islands in Hawaii. What you are going to have are groups of layers of the same approximate age, with different members of the groups in different places. The rock layer that exists now on the surface in Oahu and the Connecticut valley both represent the current age. Likewise the layers that existed on the surface 100 or 1000 or whatever years ago represent the age of the earth at that time. Note that in some areas the surface is eroding away to expose older layers, and in some areas it is building up new layers, and some new building layers are formed from old eroded layers, formed into new layers. Thus if you arrange the layers all over the earth in a chronological by depth order you will have a number of discontinuous layers included in different areas, and you will have something like:
a1 a2 a3 a4
Where any member of the A group will be over any member of the B group that occur in the same location.b1 . . b2 c1 c2 . c3 --iridium-- . d1 d2 . e1 e2 e3 e4 --volc.ash-- ...etc You may or may not find areas where a1 and a2 both occur to see which is over the other, but you can still build up a relative chronology in every area by the layers. Geologists give groups of layers of the same relative age names according to their age, a system of relative dating of formations that is as old as the law of superposition. Is there one location that has a layer that represents every known geological age? Probably not, but that is not necessary for the "geological column" to be a valid concept of relative age. See Geologic time scale - WikipediaGeologic time scale(Redirected from Geological column) quote: Each era is represented by a group of layers, all of which are above or below the group of layers that make up the other eras.
Is there any place on earth where the column exists in its entirety? Geologists don't expect the "geological column" to exist in its entirety in any one area, but they do expect the overall pattern of superposition of newer layers over older layers to occur in all locations, and use the term "geological column" to refer to this general pattern of superposition, rather than to a specific column. Is there any place on earth where you can link a path between layers in direct absolute chronological order representing every (known) era/age of the earth? Yes. For further reference see PRATT CD101 (Talk Origins)quote: Does that help? Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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RAZD Member (Idle past 1665 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi Peg, sorry for the delay in reply, but I wanted to give this some more detail.
How consistent is it? As others have noted, it is very consistent, and more to the point, in those places where it does not appear to be consistent, there are reasons for in the inconsistency. Thus a look in one small area may display an anomaly, however when you look at the larger picture it becomes clear. The overthrust mentioned is a clear demonstration of this.
ie, if we choose a random location and dig down, would the rock strata be in that sequence? The layers that are present in that location would be in order, provided that they had not been disturbed later by some other geological process (such as an overthrust). Note that some layers could be missing whole eons due to erosion, so there could be gaps in different locations. The layers would not be out of sequence (ACB instead of ABC), and this can be further checked by that other part of the superposition law: that the first formed layer controls the shape of the bottom of the next layer: one can look at the interface and determine which is the "first formed" side and which is the "second fit" side. Thus if you did find an area with ACB layers and you looked at the interface between B and C you would see that B conformed to C rather than the other way, thus these layers had been inverted before A was added.
and how reliable and consistent are the ages assigned to the different life-forms found in the layers? The ages assigned to the rock layers are very reliable and consistent (see previous post). The ages assigned to the different life-forms found in the layers are the ages of the layers. When we look at the areas where fossils are discovered, they are of interest to the paleontologists because the upper layers have eroded away, and they don't have to dig as far down to uncover the ages in question. For example, where Tiktaalik was discovered: BBC NEWS | Science/Nature | Arctic fossils mark move to land
quote: Why the Canadian arctic? Tiktaalik roseae: The Search for Tiktaalik
quote:(image used above is from Geosciences and Environmental Change Science Center | U.S. Geological Survey) The big white area at the top is Greenland. The find was on Ellesmere Island which abuts Greenland at the top of the map. It is shown in green here:Erreur HTTP 404 - Non trouv | HTTP Error 404 - Not Found - All Versions and how reliable and consistent are the ages assigned to the different life-forms found in the layers? We find very few organisms that span eons of time, and those that do, still show changes - the Coelacanths for instance, where modern ones are a different genus, live in a different ecology and are much larger than any of the prehistoric ones from the age of dinosaurs. There are also few organisms that span large geological areas. Some organisms are more universal in geological area covered, while their species are also closely related to the age of the rock layer/s they are found in. For instance foraminifera are used as an index fossil: Biostratigraphy - Wikipedia
quote: Foramins are used as an index fossil to gauge the of the age of the rock until radiometric data can confirm it, because they are in so many layers of (marine) sedimentary rock, but each species is only found in a narrow age band. http://www.gomr.mms.gov/homepg/whatsnew/papers/biochart.pdf This chart lists the geological time on the left, the various ages and eons under the CHRONOSTRATIGRAPHY heading and the different foramin species under the BIOSTRATIGRAPHY heading. If you search the chart for Globorotalia tosaensis tosaensis, for example, you will find that it is only listed during one of these age layers in the lower Pleistocene, or Calabrian stage, and thus finding this species of foram would indicate the rock was from this period. Curiously, not only do we have confirmation of the relative ages with radiometric ages for the rocks that foramins have been found in, we also have the full evolutionary picture of the diversity and development of the different species: Geology Dept article 3
quote: They have been able to show the evolution of almost every species of foram from generation to generation, thus validating the relative ages of the layers and the sequence of age of those layers. Not only do the layers correlate with radiometric ages, but they correlate with the changes over time of the species found in them. Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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RAZD Member (Idle past 1665 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi Peg,
Charles Lyells book 'Principles of Geology' explains that all sedimentary rocks are deposited by extremely slow processes, such as rain washing loose sand down a mountain slope to a river. Sir Charles Lyell was a contemporary of Darwin and a leading proponent of uniformitarianism: Charles Lyell - Wikipedia
quote: If anything Lyell may have overemphasized the gradual processes observed in geology in so many areas, however I am sure he was aware of certain abrupt processes, such as volcanic lava and ash deposition, in addition to what is mentioned by Vacate and Percy. Certainly, when we look at the layers of index fossils, such as the foraminifera, the gradual deposition of sediments makes sense because the organisms are different in the different layers, and in some cases can be observed to change in single layer groups.
Is this theory still current today? Or has it changed? There have been several advances in geology that have affected the way the rocks and layers are regarded, with Plate Tectonics being the most radical change in thinking, and with radiometric dating operating as a validating check on the relative ages determined by superposition, but by and large the principles are still valid, albeit modified by modern thinking (just as evolution is modified by modern thinking from Darwin's formulations). History of geology - Wikipedia
quote: So yes, I would say that the field has changed since Lyell's book, and that it has grown more complex, building on the earlier knowledge and theories and how they explain all the evidence.
the other thing i want to know is why geology and evolution are so closely linked? You can probably do significantly valid geology while knowing very little about evolution. Evolution helps to present some order to some layers via index fossils, but it is not necessary for the understanding of plate tectonics, uplift, superposition, etc. Geology involves understanding the record of the natural history of the planet, and just as written history records events, so too does the geological record record the history of past events, including floods, volcanoes, earthquakes and the long durations of seas. This would be so even if no organisms formed fossils. That certain organisms under certain conditions form fossils means that their actual individual existences in the past are recorded in the natural history of the earth. This record is not evolution, nor is it part of the theory of evolution, it is the record of what actually lived, and of what happened (floods, earthquakes, volcanoes, meteors, etc) to life in the past, whether evolution is a valid theory or not. Life occurs in the present, so it is always acting on the surface, and what is left behind, to be covered by sediments and volcanic ash and the like, are small bits and pieces of the life that was occurring at the time those sediments and ash layers formed. For the theory of evolution to be complete, in the sense of explaining all the known evidence, it needs to be able to explain not just what we see living around us today, but what we know of past life, from the geological record (climate and ecosystem), from the paleontological record (fossils), from the anthropological record (paintings and artifacts), as well as from the historical record (descriptions of dodos, etc, that are now extinct). Understanding geology is essential to understanding that part of evolution that deals with ancient life, however it is relatively irrelevant to the continued process of life in the world today, acting as the canvas upon which the picture of modern life is drawn.
Shouldn't they be independent of each other? Shouldn't all knowledge tie together into a unified whole? Astronomy tells us about stars and planets, physics tells us how they form and thus how the earth formed, chemistry tells us how molecules act and biology tells us about how life behaves. Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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RAZD Member (Idle past 1665 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi Mr Jack
Charles Lyells book 'Principles of Geology' explains that all sedimentary rocks are deposited by extremely slow processes,... No, it doesn't. It explains that all geological phenomena are explicable by processes that continue today. Much of that is extremely slow, but Lyell most certainly does not exclude the operation have rapid forces - ... Excellent distinction.
... - in fact much of the Principles is occupied with discussion events such as volcanoes and earthquakes. Floods and landslides are also discussed. You can find the entire book on-line at:ESP Digital Books: Principles of Geology, Vols 1-3 Chapters 18 to 26 are devoted to volcanoes and earthquakes. Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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RAZD Member (Idle past 1665 days) Posts: 20714 From: the other end of the sidewalk Joined: |
Hi again, Mr Jack
That's the first edition, is it not? It's the 1830 edition. Lyell, Charles 1830. Principles of Geology, Vols 1-3. London: John Murray Check out other publications available from this sourceESP What's New Wright, Sewall. 1931. Evolution in Mendelian populations. Genetics, 16:97-159. Dobzhansky, Th. and Queal, M. L. 1938. Genetics of Natural Populations. I. Chromosome Variation in Populations of Drosophila Pseudoobscura Inhabiting Isolated Mountain Ranges Genetics, 23: 239-251. Haldane, J. B. S. 1934. A Mathematical Theory of Natural and Artificial Selection Part X. Some Theorems on Artificial Selection Genetics, 19: 412-429. Some pretty good stuff and original sources for a lot of older works not normally on line. But this is getting off topic. Might be a good Links and Information item. Enjoy. by our ability to understand Rebel American Zen Deist ... to learn ... to think ... to live ... to laugh ... to share. • • • Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click) • • •
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RAZD Member (Idle past 1665 days) Posts: 20714 From: the other end of the sidewalk Joined:
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Then the fossils of course go along with the depositional environments: so we get marine fossils in limestone but terrestrial fossils in aeolian sandstone, for example.
And the fossils fit into the temporal geological matrix, closely associated with other fossils that are nearby in the matrix, with ancestral fossils nearby geologically but in older rocks, while descendant fossils are nearby geologically but in newer rocks.
... So you get the different marine deposits (siliceous ooze, calcareous ooze, pelagic clay) represented by chert and limestone and pelagic claystone respectively; you get deserts represented by aeolian sandstone; you get swamps represented by coal measures; ... Similar habitats in different parts of the world often have different fossils, just as we see in the distribution of species in the world world today, and this too ties in to their position in the temporal geological matrix: you don't find fossils without nearby ancestors or descendants in earlier and later rocks. This matchup in time and space was discovered by both Darwin and Wallace, Darwin going on to write his book on evolution, and Wallace going on to concentrate on Biogeography, as I noted in the Alfred Russel Wallace and Biogeography thread, Message 1:
quote: There you have the temporal geological matrix spelled out in 1855. Wallace is known as the father of biogeograpy. I can recommend David Quammen's book, The Song of the Dodo, which can be downloaded as an e-book or read on-line HERE: it is a very readable book that doesn't require a lot of scientific knowledge to understand. Enjoy Edited by RAZD, : .by our ability to understand Rebel☮American☆Zen☯Deist ... to learn ... to think ... to live ... to laugh ... to share. Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)
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