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The earth is an ever-changing chunk of rock to put it at the lowest level of comprehension available This rock that we call home is brewing with billions of life forms and is constantly changing every day This can be attributed to the various cycles that are at work on this planet of our from the hydrological system to the rock cycle the earth is an ever changing form Pennsylvania is just a small part of this system we call our home Formed millions of year ago by tectonic collisions and molten rock Pennsylvania is a part of the earth full of specially minerals and geological features that stand out as being come of the best in the world What would our state be with out its coalmines and steel mills Which of course are only possible through the unique geographic features of our state The Pre-Achaean Achaean and Proterozoic Eras Geologists believe that Pennsylvania was formed by parts of the Laurentian continental crust block This crust block is made up of many micro plates which were accreted during the period from about 25 billion to 10 billion years ago This was previously part of an even larger crustal block called Rodinia Geologist believes that PA is full of rocks that were once part of this crustal block These rocks are known as the Greenville rocks Greenville rocks are metamorphic rocks composed mainly of gneiss Some of these rocks are visible in Southeastern PA but most are buried deep within the surface of PA The Cambrian and Ordovician Periods This is really the period that life started to develop in the state of Pennsylvania Now how did life star in this state you may ask well here is how At the start of the Cambrian period water from the Ocean spread inland across North America Pennsylvania got in the way of this and was covered with a shallow layer of water
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