Textbook Notes (363,474)
Canada (158,377)
EESA06H3 (234)
Nick Eyles (205)
Chapter 19

Chapter 19

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University of Toronto Scarborough
Environmental Science
Nick Eyles

Chapter 19: Time and Geology Determining age relationships between geographically widely separated rock units is necessary for understanding the geologic history of a region, continent, or whole Earth What is Uniformitarianism? In 18 century, James Hutton, father of modern geology o Realized that geologic features could be explained through present-day processes o Mountains are not permanent, but have been carved into present shapes and will be worn down by slow agents of erosion now working on them o Great thicknesses of sedimentary rock are products of sediment removed from land and deposited as mud and sand in seas o 1788- we find no sign of a beginning-no prospect for an end Charles Lyell- Huttons concept that geologic processes operating at present are the same processes that operated in the past as the principle of uniformitarianism o The present is the key to the past Suggests that changes take place at uniform rate, but sudden, violent events also influence Earths history o Some countries used actualism instead Dating based on radioactivity allows us to determine a rocks numerical age (absolute age)- age given in years or some unit of time Geologists more concern with relative time, the sequence in which events took place Relative Time Geology of Grand Canyon can be analyzed in four parts: o Horizontal layers of rock o Inclined layers o Rock underlying the inclined layers (plutonic and metamorphic rock) o Canyon itself, carved into these rocks Principles Used to Determine Relative Age Contacts are particularly useful for deciphering the geologic history of an area o Contacts: the surfaces separating two different rock types or rocks of different ages) Formations: bodies of rock of considerable thickness with recognizable characteristics that make each distinguishable from adjacent rock units Stratigraphy: uses interrelationships between layered rocksediment to interpret history of area or region o Uses four principles to determine the geologic history of locality or region: Original horizontality: States that beds of sediment deposited in water formed as horizontal or nearly horizontal layers Superposition: within a sequence of undisturbed sedimentary or volcanic rocks the payers get younger going from bottom to top Lateral continuity: an original sedimentary layer extends laterally until it tapers or thins at its edges Cross-cutting relationships: a disrupted pattern is older than the cause of disruption Contacts representing buried erosion surfaces such as these are called unconformities Inclusion: fragments included in a host rock are older than the host rock Pages 513 to 516 for examples Unconformities www.notesolution.com
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