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Chapter 8 Summary

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I have learned about catastrophism that they believed that earth features have formed suddenly.The modern theory of earth called uniformitarianism states that the forces those are shaping ourearth today also shaped in past. The slow and weak processes produces great result over longtime. But we have no human evidence that can tell us about past. Rocks record the geologicevents that occur in past. Earth is very old and have its surface and interior many times. Today byusing radioactive dating we can found the numerical date of rocks. By using the sequence offormation of rocks we can estimate the relative date. Law of superposition states if the rocks arein undisturbed state then every rock is older than the rock present above it. Principle of originalhorizontality sates that sedimentary layers are in horizontal position. I have also studied aboutmany principles like principle of lateral continuity, cross-cutting, inclusions. When layers aredeposited without interruption then they are called conformable and if there occur interruptionthen it is called unconformity. There are three types of unconformity, angular unconformity,disconformity and nonconformity.Fossils are used to interpret past. There are many type of fossils like molds and casts,carbonization and impressions, amber and some occurs as traces. For Geological time scale,rocks are match according to age and this process is called correlation. Rocks can be correlatedaccording to fossils. Principle of fossil succession stated that fossils are arranged in age orderthan they do not represent random picture. Radioactivity can be used to determine numerical age.There are three types of radioactive decay. Other methods include Half-life, isotopes, carbondating.Earth age is divided into several units in Geological time scale including eons, Phanerozoic,these are sub-divided into eras and eras are divided into Paleozoic, Mesozoic and Cenozoic. Ageof all the rocks cannot be accurate age of rock cannot be determined. Determine by radiometric.In sedimentary rocks, the grain are of different ages, similarly in metamorphic rocks, the agecannot be accurately determined. So for determining the age of sedimentary and metamorphicrocks, these rocks must be compared with igneous rocks.I have learnt that radioactive dating is useful for determining the numerical age of rock. It cannotdetermine accurate age of sedimentary and metamorphic rocks but their age can be determine bycomparing with igneous rocks. Until any accurate method not developed, radioactive dating canbe used for numerical age determination.I have a question for you guys, what are the other methods of correlation of

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