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Geologists use several principles to find the relative age of geologic layers. Remember, contact metamorphism is changes in a rock due to contact with magma or lava.- The principle of superposition is simply the fact that the lowest layer of a rock formation is the oldest layer while the youngest layer is towards the top. Think of it as a boundary layer between igneous rocks and sedimentary rocks.The goal of this lecture is come to come to a scientific understanding of geologic time and the age of the Earth.In order to do so we will have to understand the following: To better understand these concepts, let's look at an archeological example: Imagine we are a group of archeologists studying two different trash pits recently discovered on the Tulane University campus and at the Audubon Zoo (where they all aksed for you).Steno formalized the laws of superposition, original horizontality, original continuity and inclusions in his publication entitled states that any inclusion is older than the rock that contains it.Steno's idea that fossils are older than the rock in which they are found hints at this principle, but Hutton is most often given credit for this principle.states that fossil organisms succeed one another in a definite, irreversible, and determinable order.Prior to the late 17th century, geologic time was thought to be the same as historical time.
When information derived from two outcrops is integrated, the time interval they represent is probably greater than that of each alone.A chance encounter between determined fishermen and a great white shark off the Tuscan coast in 1666 sparked a chain of events that would help change humans views of fossils and Earth’s geologic past (Cutler 2003, pp. Nicolas Steno (1638-1686) dissected the head of this shark and realized fossil tongue stones believed to be petrified snake or dragon tongues were actually fossil shark teeth (Prothero 1998, p. One problem still existed, how do fossils become embedded in solid rock?Steno recognized that fossils represent organisms that became buried in sediment, which later turned into rock.Furthermore, useful fossils are either rare or totally absent in rocks from Precambrian time, which constitutes more than 87 percent of Earth history.Precambrian rocks must therefore be correlated by means of precise isotopic dating.
By carefully digging, we have found that each trash pit shows a sequence of layers.