![]() ![]() ![]() Emphasize the contrast between fast and slow changes. (ESS2.B)Ĭonstruct an explanation about changes in Earth’s surface that happen quickly or slowly. Examples of models could include valleys, canyons, or floodplains and could depict water in the solid or liquid state. This mountain range formed slowly over the course of tens of millions of years and caused the sedimentary rocks in Cedar city to become tilted as part of an ancient fold in the layers.ĭevelop and use models illustrating the patterns of landforms and water on Earth. This led to the formation of a tall and extensive mountain range. This plate pushed and compressed the continent causing the layers of rock to buckle and fold. Over 100 million years ago there was a plate near the western coastline of paleo-North America that was moving eastward. This layer has broken into distinct puzzles like pieces that can move and interact with each other. If you guessed that plate tectonics caused the layers to tilt then you are correct! Earth's outermost layer is composed of rigid and brittle material called the lithosphere. This tilting occurred slowly millions of years ago as tectonic activity caused large mountains to form in this area. If sedimentary layers are found in a position that is not horizontal then we can guess or infer that something must have moved the layers into a different position.Īre the rock layers in a flat position? What could have caused the layers to move into an inclined or tilted position? The image above shows one of the sedimentary layers called the Moenave Formation tilted at an angle of about 55° from horizontal. This principle explains that sedimentary rock layers are initially formed or deposited in a horizontal or flat position. Therefore if horizontal strata are dissected by erosional features, such as a valley, they can be interpreted to be the same strata.There is a scientific principle in geology called the principle of original horizontality. Sediments are deposited laterally in continuous layers. See Original Horizontality and Superposition. Therefore, if rocks are tilted, folded or metamorphosed, then these events must have followed deposition and lithification. Sediments deposited or precipitated on the Earth’s surface accumulate in horizontal layers. Therefore the principle of uniformitarianism is expressed as “the present is the key to the past” which guides the principles of stratigraphy. ![]() For example, the processes that transport and deposit sediment in a river are the same today as they were a billion years ago. Natural processes such as erosion and deposition, plate tectonics and the laws of gravity and isostasy produce the features of the Earth. Hutton realized the events in the earths past can be understood by observing the processes seen today. The principle of uniformitarianism was first stated by James Hutton in the 18th century. To determine the sequence of geologic events, several principles must be followed. The sequence orders the events but provides no information to the amount of time passed or between events. It is a qualitative way of describing the sequence of events. Placing of events in the order in which they occurred without any relationship to the actual time during which any one event occurred is known as relative dating. Cindy Kearns and Elizabeth Johnson Relative Dating ![]()
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