An evolutionary sequence can be determined by

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An Introduction to Physical Science
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Chapter 11 / Exercise 1
An Introduction to Physical Science
Shipman/Wilson
Expert Verified
established. An evolutionary sequence can be determined by applying the Principle of Superposition. (Younger fossils will be deposited over older ones in undisturbed sequences of strata) Index FossilsFossil records of species that appeared, and changed relatively rapidly over time. Index fossils are widespread and found in many rock types. They are the best indicators of relative time. The Fossil records show the old primitive fossils and the younger more developed fossils.
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An Introduction to Physical Science
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Chapter 11 / Exercise 1
An Introduction to Physical Science
Shipman/Wilson
Expert Verified
Geological time The geological time scale was devised in the 19th century before radioactivity had been discovered. The subdivisions mark major changes in the fossil record. Much later absolute ages based on radiometric dating were added. (refer to a geological time scale picture in order to understand what I mean by subdivisions) Relative Dating ThePrinciple of Superposition and the Principle of Horizontality are used to determine the order of events in rock outcrops. If sedimentary rocks is undisturbed the lower strata must be older than the strata above it The Principle of Cross-cutting relationships is also important. Principle of Cross-cutting If two strata are faulted. The faulting occurred after the youngest rock affected. If an igneousintrusion cuts across strata, then it is younger than the affected rocks. (such as a dike cutting into other older igneous rock) Stratigraphersfrequently use the knowledge of different principles to determine the relative ages of strata in a rock outcrop and the sequence of events. Absolute Dating Rates of Erosion For instance, by knowing the rate at which a waterfall is cutting back the rock, and assuming the rate has been constant in the past, we can calculate the age. This only works locally. In other words we can’t use this kind of dating for things much further in the past. (Dinosaurs etc.) Rates of Sedimentation We can calculate how quickly sediments are deposited in deltas or along coasts by observing the thickness of deposits covering archaeological remains. Again like rate of erosion. This only works locally. Growth rates of Plants or invertebrate animals For instance, the time of deglaciation in northern areas can be calculated by measuring the size of particular lichen covering boulders, since the yearly growth rate of these lichens is well known Recurring Features Fossils or sediment that relate to daily, seasonal or multi-year cycles. A good example is a rhythmic yearly sedimentation of silt and clay laminations that form the glacial lakes. The very small silt particles get transported in the summer and then settles to the bottom. The clay however can’t settle without stagnant water so when the water gets ice
over it it becomes stagnant enough for it to settle. Thus you get a silt-clay couplet, called a varves, and can determine the lake ages. Radiometric Radiometric methods are based on the fact that certain radioactiveelements are naturally unstable.

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