Why are caves usually found in limestone-rich regions?
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In addition to the previous answer, the acidity of the water plays a significant factor.  Water alone is a great erosive tool, but rock is fairly resilient and it would take a long time to create the cave systems.  However, Calcium Carbonate (limestone) reacts with acids and disolves when in contact with them.  An eyedropper full of a diluted hydrochloric acid will create a small hole in a sample of limestone.  So the question now becomes where does the acid come from?  Well, pollution definately plays a factor, however natural acids in the soil are leeched down into the limestone as water works its way into the limestone.  This is also why sinkholes occur... imagine a cave system with a roof or ceiling allready in place, and years of acidic water leaching into the cave through the cieling.  Eventually it will disintigrate, collapsing in on itself.  You can check out www.geology.com and search Karst Topography for more information.
142267
I think there is some over-generalizing going on here. \n\nThe short answer: Granite is going to be more susceptible where its crystalline grain structure can be attacked by mechanical weathering. Limestone is going to be more susceptible where its softness is a disadvantage to mechanical weathering. For many types of mechanical weathering there is going to be little difference. \n\nHave you ever been to Yosemite? Half Dome, in the famous photographs by Ansel Adams is a perfect example of exfoliation of granite in sheets. This is a mechanical weathering process related to pressure release. Granite might be more susceptible to this (I am speculating) but only because it is often being unburied from much greater depths. Jointing in limestone is often related to pressure release. \n\nTo answer this question properly you need to consider the different types of mechanical weathering. I will compare the ones I can think of.\n1. Exfoliation caused by pressure release:  From my own field observations in areas where glacial unloading has occurred I would say that this affects both granite and limestone in a similar manner. Both will break off in sheets or blocks. \n\n2. Exfoliation is caused by temperature change: I have no quantitative proof but my opinion based on observation is that limestone is less susceptible to this because it is held together by cement and internal porosity probably has some ability to absorb differential expansion. Granite on the other hand is composed of crystalline grains that have different expansion rates and are likely to split apart. \n\n3. Freeze-thaw: Limestone does have bedding planes, and often has jointing as well, that is susceptible to this.  Some limestone has open porosity that also will be subject to some freeze expansion. Probably limestone is more vulnerable to this. Granite is going to be slightly susceptible to this only to the extent that water can penetrate it or to the extent it has been jointed or weakened by exfoliation. \n\n\n4.  Abrasion: Wind erosion affects both limestone and granite. Limestone is softer so windblown sand grains are more likely to erode the limestone. \n\n5. Salt-crystal growth: This is very common in coastal settings and sometimes in desert settings where moisture in the air is likely to contain some salts. Many of these salts will expand as the moisture that carried them evaporates. Heat will also cause them to expand.  I would say that granite is again more susceptible because of its crystalline grain structure. However, there is a special situation for limestone that few people who have never been in a cave have ever observed. Limestone often contains small deposits of anhydrite within the limestone. Anhydrite is unstable under surface pressures and tends to absorb water becoming gypsum. It expands as it does this and causes the limestone to break, often in sheets, but sometimes in blocks.  In many caves this is a primary cause of ceiling collapse and it can even result in stoping (raising the ceiling of the cave upward). \n\n6. Trees, plants: I doubt that there is any difference here. Some granite might provide more nutrients from chemical weathering to plants than limestone does, and so encourage its own destruction by plant roots, but both rocks are going to be susceptible. \n\n7. Tectonic and regional jointing: Tectonic events can cause fracturing in both types of rock. Limestone might be more flexible and be less susceptible to fracturing from mild folding. Regional jointing is related to pressure release and depends more on the burial and unroofing history than the type of rock. I don’t think either one is going to be more or less susceptible in most situations. Limestone often exhibits joints that can be traced for tens of miles that are related to regional stress regimes (both shear and extensional) and I believe that granite will produce similar joints.  You might be surprised to learn that the shear strength of granite and limestone are very similar
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Hey does your question mean - how does fossilation happen\n\nMost fossils are found in sedimentary rocks, those rocks produced by the accumulation of sediment such as sand or mud. Wind and other weathering conditions wash away sediment on land, depositing it in bodies of water. For this reason, fossils of sea creatures are more common than those of land creatures. Land animals and plants that have been preserved are found mostly in sediments in calm lakes, rivers, and estuaries.\n\nThe likelihood that any living organism will become a fossil is quite low. The path from the organic, living world to the world of rock and mineral is long and indirect. In the best conditions, fossilization will occur if an animal or plant dies and is quickly covered over with moist sediment. This prevents the animal or plant from being eaten by other organisms or from undergoing natural decay through exposure to oxygen and bacteria. The soft parts of an animal or plant decay more quickly than its hard parts. Teeth and bones are therefore more likely to be preserved than skin, tissues, and organs. Because of this fact, most fossils come from the time period dating to almost 600 million years ago, when organisms began to develop skeletons and hard parts.\n\n=====================================\nAm not too sure of my German\n\nDie meisten Fossilien werden die von der Ansammlung der Ablagerung in sedimentären Felsen, die Felsen gefunden werden hergestellt wie zum Beispiel Sand oder Schlamm. Wind und andere Verwitternbedingungen waschen weg Ablagerung auf Land, deponierend es in Gewässern. Aus diesem Grund sind Fossilien von Seenkreaturen gemeinsamer als jene von Ländernkreaturen. Landen Sie Tiere und Pflanzen, die bewahrt worden sind, sind gefunden größtenteils in Ablagerungen in ruhigen Seen, Flüssen, und Gezeitenmündungen. \n\nDie Wahrscheinlichkeit, die irgendein lebender Organismus ein Fossil werden wird, ist ziemlich niedrig. Der Pfad vom organischen, Welt zur Welt von Felsen und Mineral lebend, ist lang und indirekt. In den besten Bedingungen wird Versteinerung stattfinden, wenn ein Tier oder Pflanze stirbt, und ist schnell über mit feuchter Ablagerung bedeckt. Dies verhindert das Tier oder die Pflanze, von durch andere Organismen gegessen zu werden, oder erlebend von natürlichen Verfall durch Aussetzung zu Sauerstoff und Bakterien. Die weichen Teile von einem Tier oder Pflanze verfallen mehr schnell als seine harten Teile. Zähne und Knochen sind daher wahrscheinlicher, als bewahrt zu werden, enthäutet, Gewebe, und Organe. Wegen dieser Tatsache kommen die meisten Fossilien vom Zeitraum datierend zu fast 600 Millionen vor Jahren, als Organismen begonnen haben, Skelette und harte Teile zu entwickeln.
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Try a museum of natural science.  You can find all kinds of fossils there.
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There is no comprehensive list available to the public. In the past some books and some maps were published that showed cave locations, however this practice in the United States at least, has changed to protect cave environments. In other countries the data is not always protected, but is seldom available anyway.\n\nMany caves have been found to contain endangered, unique species, often specific to a single cave, and most caves have delicate rock formations that can be damaged by the uninitiated visitor. Occasionally you hear of some sort of rescue effort to recover someone from a cave that entered without proper equipment and preparation and this hysteria has added to the protectionist attitude by government agencies. Fear of liability lawsuits keeps most private landowners from wanting the locations to be known as well.  Most Federal agencies that have caves on their lands will not allow cave visitation without permits. \n\nMany state cave surveys, affiliated with the National Speleological Society, do have some of this data, but it is private property and is not shared with the public. \n\nIf you are interested in visiting caves I suggest you join the National Speleological Society and find a local Grotto to join. \nhttp://www.caves.org/\n\nThe Grotto list is at:\nhttp://www.caves.org/io/grottos.shtml
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Index fossils should occur over a broad geographic range and a very limited time span.  If a group of fossils occurred over the broad range you mention above...they would be lousy index fossils..\n\nThe whole idea of an index fossil is that if you were to find one in the rock record that you would know it occurred at a very restricted time..this identifying that layer of rock as that particular time.  the time range you have listed above covers the entire geologic history of the world except the pre-cambrian.\nthe answer to your question is no.
690069
Good question.\n\nLimestone is found in the earth.  Refined Limestone and limestone in it's pure form is known as Calcium Carbonate.  (CaCO3).\nIf you mix limestone with water, you'll get some mixing, but not all the limestone will go into solution.  What did go into solution can be "painted" onto a wall but it won't stay past the next few rains.  \nIn order to use limestone for paint, it has to be refined.  In other words, it has to go through a chemical reaction such as Carbonation, in order to get the product that you desire.  \nPlease see my sources for more information.
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No, limestone becomes marble under enough heat and pressure. \n\nShale is formed from clay.\n\nBy the way, almost NO limestone is formed from chemical precipitates from seawater. It is formed from the remains and shells of living organisms, like clams, oysters, coral, algae, and bacteria.
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Potential problems include: \nDestruction of habitat:  caves (important) or the soils of lime-loving species.\nPotential for contamination of groundwater supplies in karst regions.\nBig trucks on the road: traffic, congestion, possibly getting gravel on the road. \nDegradation of landscape: Some people don't like the look of quarries
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One of the arguments would be the lack of fossils for intermediate species. As there are many fish and reptiles fossils discovered, shouldn't there be at least some half fish-half reptile fossils as well?
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Karst!       At least this is the terminology for the type of landscape created by dissolution of limestone, dolomite, gypsum and rarely quartzite. This is the landscape that contains caves, sinkholes, and  dolines.  \n\nThe process is initiated when rain water picks up carbon dioxide in the atmosphere and then picks up even more carbon dioxide as it seeps through soil. Soil often has a carbon dioxide content as high as ten percent so the water may become very acidic, since carbon dioxide combines with water to form carbonic acid.  As the water permeates downward it encounters bedrock. In limestone this bedrock is often fractured and where the water begins to penetrate the rock the carbonic acid will dissolve the limestone, which is calcium carbonate. These fractures will gradually enlarge creating an irregular zone where the soil contacts the bedrock. If the carbonic acid content of the water is high enough, or its penetration rate is fast enough, it will sink into the rock until it hits some sort of a barrier and there it will begin to dissolve away rock. This will eventually become a cave.  Other types of landforms that will develop are sink holes. Sink holes are large pits that form under the soil surface, sometimes by cave collapse, and sometimes just by dissolution. Some areas of the world are dominated by sinkholes, like parts of Puerto Rico and Jamaica's cockpit country. \n\nOther caves that have formed by this process are Mammoth Cave in Kentucky, USA, which is the worlds longest cave. Mammoth Cave is has about 367 miles in length that have been mapped so far, and mapping continues. Another famous cave is Carlsbad Caverns in New Mexico. Carlsbad Caverns was formed by a different type of dissolution when groundwater mixed with sulphur compounds, possibly during petroleum generation or migration, and formed sulphuric acid which is believed to have moved upwards into the ancient Capitan reef rock and dissolved enormous cave passages. Another type of cave forms where different types of groundwater such as saltwater and freshwater mix together in the subsurface. These are called mixing zone caves and they can form at great depths where the reaction between the two solutions creates a potential for dissolution of limestone. \n\nThe Arabika Massif, Western Massif has recently been mapped as the world's deepest cave at –2080m (6824 ft). The Optimisticeskaja in Ukraine is the world's third longest cave and the world's longest gypsum cave at 133 miles. \nhttp://www.pipeline.com/~caverbob/wlong.htm\n\nIn Brazil there is a cave formed by dissolution of quartzite, the Caverna do Centenário and I believe there are some examples of this in Venezuela as well. \nhttp://www.showcaves.com/english/br/caves/Centenario.html\n\nKarst landscapes tend to be some of the poorest in the world because they are difficult to farm. Other problems associated with karst are collapse of sinkholes, such as those that happen occasionally in Florida, taking houses, cars,and everything else down into the hole. Contamination of ground water is a difficult problem in karst areas because the spill of a contaminant can quickly move through a complex underground drainage system in ways that are difficult to predict unless there has been considerable dye tracing of the karst system. One fear of karst scientists around Mammoth Cave is that a spill of a dangerous material on the nearby interstate could contaminate large parts of the cave system within hours or days. \n\nAs for other less dramatic effects of bedrock dissolution, most rainwater does pick up some rock as it percolates downward toward the water table. Most often this solute ends up in the groundwater and is the reason some well water is described as 'hard' water since it has a taste that is given to it by the dissolved minerals. In most areas this dissolution is so insignificant that it does little to change the land surface.
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Regarding chambers beneath the Sphinx - yes, ground penetrating radar studies have revealed several anomalies, none very big, that are probably chambers. It is not clear how many of these reflect natural fissures in the limestone or how many are actual deliberate constructions. It is known that some of these chambers are of fairly recent date - the 1800s, made by explorers and/or in the course of restoration efforts. It is extraordinarily unlikely that there is either a "Chamber of Lost Records" as predicted by Edgar Cayce, nor a "machine" of Atlantean provenance associated with the Sphinx.\nIt is not entirely beyond possibility that there is an ancient chamber dating to the period of the carving/construction of the Sphinx or to later restoration efforts by Tutmose IV and later kings. Such a chamber(s) would likely be a foundation deposit - quite common for constructions of a religious nature in ancient Egypt.\n\n\nSee the following and links therein for a decent summary:\nhttp://www.catchpenny.org/chamber.html...
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Karst springs are commonly formed by the collapse of the roof of water filled cave passages. In other places the caves open into areas where some other form of erosion like stream and river channels have cut down through the cave and captured the water flow. Many rivers have karst springs in them that supply a great deal of the water to the river. Mammoth Cave in Kentucky, the world's longest cave at 367 miles, drains into the Green River through a spring. \n\nThe caves are initially formed by dissolution of limestone or other soluble rock (there are caves in gypsum and even quartzite) either by rainwater that carries dissolved carbon dioxide (carbonic acid) or by other types of acids that may be in the water. The dissolution of small cracks in the limestone eventually grows into large cave passages, and at some point often emerges from the earth surface at a spring. \n\nHere is an illustration that shows a "resurgent stream" or karst spring:\nhttp://www.cancaver.ca/docs/karst.htm
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Carbonic acid is the one that usually affects limestone bedrock.\n\nCarbonic acid forms when decaying matter interacts with filtering water.\n\nAs it moves down through cracks in the bedrock, it slowly dissolves the limestone. Over time the cracks grow & enlarge eventually making miles of underground caves & caverns.\n\nThe type of topography associated w/ dissolution of limestone bedrock is called Karst Topography.\n\nKarst simply refers to that which you can see above ground like sinkholes (collapsed caverns/caves) & Karst lakes (sinkholes filled w/ water).
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its formed by the dissolution of a soluble layer or layers of bedrock, usually carbonate rock such as limestone or dolomite ..\n\nKarst landforms are generally the result of mildly acidic water acting on soluble bedrock such as limestone or dolostone. The carbonic acid that causes these features is formed as rain passes through the atmosphere picking up CO2, which dissolves in the water. Once the rain reaches the ground, it may pass through soil that may provide further CO2 to form a weak carbonic acid solution: H2O + CO2 → H2CO3. Recent studies of sulphates in karst waters suggests sulphuric and hydrosulphuric acid may also play an important role in karst formation.\n\nThis mildly acidic water begins to dissolve the surface and any fractures or bedding planes in the limestone bedrock. Over time these fractures enlarge as the bedrock continues to dissolve. Openings in the rock increase in size, and an underground drainage system begins to develop, allowing more water to pass through and accelerating the formation of underground karst features.\n\nfor more try http://en.wikipedia.org/wiki/Karst
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Some rocks are formed from magma (lava) that comes from deep in the earth. THose rocks never have fossils because, hey, they were like, 2000 degrees and anything close to them was burned totally. \n\nSome rocks were formed from deposits at the bottom of ponds, rivers, mud flats along the ocean, and in the shallow ocean. Those kinds of rocks (shale, limestone) can have lots of fossils. Let's say that you had a pond at the end of a river where it meets the sea. Lots of dead stuff could float down the river and get caught in the mud. Then it would gradually get covered by more mud. After thousands or millions of years the mud would be really thick. It would be formed into rocks with the remains of the dead animals in it. Bingo. That's a fossil. \n\nThere are lots of grat books about fossils. Check it out at your local library. And most places in the USA there are rocks near you where you could go and dig up your own fossils. That would be cool.
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Groundwater dissolves the rock underground.  This mainly occurs in carbonates because they are common and easily dissolved.