Dating of fossils and rocks
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Great Rift Valley system Noun xi of faults and other sites of tectonic activity stretching from southwestern Asia to the Horn of Africa. Suppose, too, that all the layers contain a good representation of the animal life existing at the time of. Geologists have studied the order in which fossils appeared and disappeared through north and rocks. Geologists call this the principle of lateral continuity. Therefore, the slate that contains the acritarch and bacteria is between 704 million years and 1408 million years old, because the pegmatite is 704 million years old and the granite is 1408 million years old. In another 5,730 jesus, the organism will lose another half of the remaining C-14 isotopes. Voted up, awesome and shared.
A sedimentary rock is just what it sounds like: it is a rock that consists of sediment! Sedimentary rocks can consist of sand, clay, chalk and fossils and as a marine geologist I find sedimentary rocks very fascinating! Some may think that sedimentary rocks is a bit dull since sedimentary rocks isn't created by violent and exciting volcano eruptions from the Earths mantle like the igneous rocks. That is one of the fascinating thing with sedimentary rocks! The other exciting part with sedimentary rocks is that they tell us about Earths history! I will tell you a little about how to do read the rocks and I hope it will help you to see sedimentary rocks in nature in a new way! Every single particle in a sedimentary rock initially comes from a rock or as soil on land. By time, the rock is broken down into small particles by weathering and the small particles are transported away. Sometimes the transportation distance is long and sometimes shorter. And most sedimentary rocks consists of small particles that have a long and fascinating story to tell from their long journey behind them. Read on and you will know why and how! First we need to make clear what sediment is! Sediment is material that occurs natural and is broken down by processes like weathering and erosion. This means that sedimentary rocks can consists of all the materials on earth and take a minute to think about the breathtaking fact that every single particle in a sedimentary rock have been transported and shaped by transportation in more than one media, and finally, that particle has settled down upon the deep ocean floor long, long time ago. It gets even more fascinating to think about that we can actually see and walk on former ocean floor that looks amazing in many places on earth. I have some pictures from such a place further down in the article. And then, when the ocean floor becomes rocks on land the weathering starts again. It is like an ongoing transportation of particles that never ends. I think you all know what weathering is but I include the definition anyway. Weathering occurs when a rock is fragmented by mechanical forces or are decomposed by chemical alteration. Mechanical weathering is done by water, wind, frost wedging, heat, ice, biological activity like roots, and since it is only mechanical influence, there is no change in the ingoing parts of the rock since the rock´s mineral composition is the same. It is only broken it down in smaller pieces. The end result is many small pieces from a single large one. Chemical weathering means that the rock goes through a transformation chemically into one or more new compounds. Since water is a great solvent water is a major force in chemical weathering. But rocks are also weathered in other ways such as through dissolution, oxidation and hydrolysis that occurs in water. All these single particles of sand, rocks, mud and clay becomes sedimentary rocks mainly by through two major ways of lithification. Lithification means a process where sediments are transformed into sedimentary rocks. Cementation and compaction are both lithification processes that transform sediments into sedimentary rocks. The necessary compaction is created by the accumulation of sediment that accumulate over already deposited sediment. By time, the weight and the heat increases and the grains are pressed closer and closer together. The compaction reduces the pore space between the particles and can in this way transform fine grained particles into more or less solid rocks. For rocks with bigger particles, the transformation to a rock comes from cementation that is created by smaller particles that fills the pore spaces between the bigger particles. Groups There are two major groups of sedimentary rocks: chemical sedimentary rocks and detrital sedimentary rocks. The most common minerals in detrital sedimentary rocks are clay minerals and quartz but they can also consist of feldspars and micas. Detrital rock are distinguished by particle size as you can see in the table above. Apart from distinguish different sedimentary rocks the particle size can also tell us useful information about the environment where the particle once deposited. Big particle size needs stronger currents to move them and so big particle size implies that the particle was settled in an stronger current. Less energy is required to transport small particles as clay and sand so then we know that fine sand can be transported by wind and smaller water currents and it takes a very calm environment for clay to settle and deposit. This is very interesting and by thinking about it we can figure out where a sedimentary rock was created. Shale Shale is a very common sedimentary rock that consists of clay and silt sized particles. Since the particles are so small they can not be seen without magnification. The particle size is very small and this means that it must have been deposited in a relatively calm environment such as deep-ocean basins or in lakes with not so strong currents. Other places where shale can form are lagoons and river floodplains. The special with shale is that this sedimentary rock has the ability to split into thin layers. This is because silt and clay particles in shale are so closely packed and the particles are also positioned parallel alignment to each other. Although shale is the most common of sedimentary rock it is not so well known as the sandstone. The reason for that is probably that shale isn't so visible and many time the shale are covered with soil or are overgrown by vegetation. The soil comes from the shale itself since shale decompose easily. This is very obvious in places where shale and sandstone are present. In such places you can see sandstone that have dramatic forms with steep edges and the shale that has much less steep slopes and shale is also often the areas where vegetation are visible. Sandstone Sandstone is a rock that contains of sand sized grains and sandstone is the second most common sedimentary rock on earth and probably the most known. The history and origin of a sandstone can often be told by the sorting of the grains, by the particle size, the particles roundness and mineral composition. For example, if the grains are rounded we can tell that the particle has been transported some distance by water. There are many different types of sandstones and the difference between them is due to the minerals in the stone. Grand Canyon, Arizona is a place where both Sandstone and Shale can be seen. Conglomerate and Breccia Conglomerate consists mostly of gravels. It can consist of large boulders and smaller gravel. The particles with large grain size can be seen visually and the spaces between the gravel are often filled with sand and mud. Breccia is pretty much the same as a conglomerate but in a breccia the particles have angular shape instead of rounded shape. The angular shape tells us that the gravel hasn't been transported very long distance from where it was deposited. Limestone Limestone is the most abundant chemical sedimentary rock and consists mostly of calcite. Most of them origins from a marine environment and consists of the skeletons of dead organism. One example are coral reefs, and the most well know coral reef is the Australian Great Barrier Reef. But there are also limestones that have an inorganic origin and consist of calcite that that was formed by chemical changes or high water temperatures. In 2002 I participated in an Excursion on Cyprus conducted by the Department of Earth Sciences, University of Gothenburg. It was 14 wonderful days on the lovely island Cyprus and I learn so much by using marine geology practically in field. One of the tasks that was given to us was to describe and interpret the formation and also date the limestone called the Lefkara formation at Petounda Point in southern Cyprus. You can see the impressive formation in the photo. Although this formation is very spectacular and special, there are so many places where you can see fantastic limestones on Earth. Chert Chart is made of silica that is very compact and hard. Examples of Chart are Flint and Agate. Chart can be found in limestone and as layers in rock. The silica in charts can be originated from organism with silica skeletons or from volcanic ash. Dolostone Dolostone is composed of dolomite that are a calcium, magnesium carbonate mineral. They are formed in seawater and is related to limestone. Evaporites Evaporites are formed when seawater evaporates. And everywhere evaporites can be found today there has been an basin submerged under seawater during Earths history. The minerals in seawater evaporates in different pace according to their solubility. Gypsum and halite are not so soluble and evaporates first and later comes potassium and magnesium salt. Coal Coal is made of organic matter such as leaves, wood and bark and other plant materials. It takes millions of years to form coal and it can only develop in a oxygen- poor swamp where the bacteria can not fulfil the decomposition of the plants. Dating fossils can for example be done by dating the rock itself or by dating the rock from its fossil content. Many times both methods are used for correlation. Through many years of research on rocks and fossils scientists has developed a geological time scale for Earth. This geologic scale has been thouroughly verified by matching rocks of similar age in different regions. Dating rocks from a rocks physical criteria can easily be done by correlation when it comes to short distances since we can find similar layers in the rocks from one place to another. But when it comes to correlation of rocks in widely separated areas it is better to correlate the layers in rock by its fossil content. This can be done because research has shown that fossil organisms succeed one another in a definite and determinable order. This means that any time period in Earth history can be recognized by its fossil content. Some fossils are more useful for dating and correlation than other fossils and these fossils are called index fossils. Index fossils are fossils that was spread over big parts of the Earth at a certain time and these fossils are therefor great time indicators. Dating fossils and rocks isn't done by using only one dating method. Instead many different methods are being used to correlate in order to be sure of the dating. It would take me several more hubs to explain in detail the methods and how it is done, and maybe I will extend this hub later with dating methods. Hi cclitgirl, Sedimentary rocks create such beautiful places and many times with wonderful colors! No wonder you want to go back there someday. Garden of Gods in Colorado Springs sounds like a wonderful place and I immediately get a view in my head with fantastic sedimentary rocks! It is funny how rocks is important to most people, but sometimes without we think about it. We become so used to see the rocks in the area where we grow up and we don't realize how much it means to us until we return or see them again. Thanks for reading and for the comment and all, cclitgirl! Speak about focusing on the wrong thing as a driver: Some rocks are really fantastic and there are so much to see, both in colors and layers. Sedimentary rocks are like an ancient book if we know the letters. I have only seen your part of the world on TV and it looks fantastic with all the formations but it must be so much more beautiful in reality. If I ever come to your part of the world, I will not be driving! Thank you so much Marcy, it is always great to see you! I think it is very common that we don't really see the things that are familiar and have always been in our surroundings. And even if we see rocks in nature, we normally don't spend so much time thinking about how and why the rocks are there! You are so lucky to have the best of both, both the fantastic rocks along the Swedish west coast and the wonderful sedimentary rocks in Greece! That would be awesome! I was so fascinated over the rocks on Cyprus when I was there, and I will never forget the beautiful nature and the clear blue sea. Mediterranian is special, so Greece is definitely in top of my list of places I will visit next time I travel somewhere. Thank you SanneL, for reading and for the wonderful comment. It is special to have another Swede here on HubPages! My purpose with this hub was to share my fascination of nature and rocks in particularly and from your comment I know that I must have done just that. Thanks for telling me, it made my day! There is something so beautiful and comforting to think about the individual particles that make a never ending journey. Thanks for reading, for the congrats and for the votes!! I appreciate it very much! I love driving through areas where you can see the layers and the colors that signify various stages of weathering and climate changes. The Southwest is particularly rich in these formations - it's almost like driving through the pages of a textbook maybe I got that in reverse - I guess the mountains were there before the textbooks were! This hub is truly fascinating and well presented! I'll admit, I don't have much knowledge about rocks, but admire people for their interest and expertise in this subject. To me there is nothing more beautiful. However, sharing my life between Sweden and Greece, I have the fortune to enjoy the nature Greece has to offer. Besides the natural advantage of abundant sunshine and history, this country also have an abundant of different rocks, which I had no idea what they were called, before I read this. Voted up, awesome and shared. Tina, thank you for a very interesting read. Sometimes it can be difficult to tell the exact name of the rock but I love them anyway and it gives me something to wonder about later. The rocks I collect remember me of the place I picked them up, and who was with me that day so it is also great memories. There are so many ways to use them and the garden or the balcony are great ideas. I am thrilled to know that you found this interesting and I wish you many more fantastic findings of rocks! Yes, it really is a fascinating subject: Oh, the Jurassic coast is a fantastic place for fossil hunting! I have never been there myself but I have heard about it, and I would love to visit it someday. To search for fossils in places like that is so fun and interesting! How lucky you are to have it near by. You must have an awesome collection of fossils and rocks at home! Thanks Lesley for the interesting comment and for reading! It is like a key to the past and sometimes a very long, long time back in time. Yes, the Sphinx has a fascinating story too and it will be interesting to follow the different ideas of its origin. Oh, I am a bit envy of people like you living in areas with sandstones! It must be so many beautiful rocks to look at in such parts of the world. Where I live, the dominating rocks are granite and gneiss and although I love the typical rocks along the Swedish west coast I would like to have some sedimentary rocks here too. Thanks Alastar for your visit and the comment! I hope you have a great day in your parts of the world! Much enjoyed learning about them here Tina. Although not a fossil the Weathering part reminds of how the Sphinx has been all but proven to be much, much older than ever thought before. Also, we have lots of quartz, mica, and sandstone over in this neck of the woods. Thanks Tina, from now on I'll know a good bit more about what's what with the sediment layers in fossil dating and such. Many rocks are simply beautiful and I am not the same person as before after my studies in geology. You must have inspired so many kids during your time as a teacher, and to have an inspiring teacher like you can make all the difference later in life! I am glad to meet another one who is fascinated by rocks: It is a fantasic area to be interested in and there is so much more to learn! Thanks for your comment, I appreciate you! Login This is necessary to sign in to the HubPages Service. Akismet This is used to detect comment spam. 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