Lecture 18 - Geologic Time

Lecture 18 - Geologic Time - Lecture 18 Geologic Time Exam...

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Unformatted text preview: Lecture 18 Geologic Time Exam 2 Grades Average = 68.3 Milutin Milankovic Obliquity (41,000 years) Seasonal Heating Glaciers and Sea Level glacial interglacial Ice Extent and Sea Level During the Last Glacial Maximum: ~20,000 Years Ago Glacial Melt and Sea Level Rise Glacier melting Kilimanjaro: ice caps have melted back by 80% since early 1900s; will be gone by 2020 All glaciers in tropics are melting rapidly Impacts: water supply, power generation, tourism, local climate and ecology Landscape developed by catastrophes James Ussher, mid-1600s, concluded Earth was only a few thousand years old Early Geologic Thinking James Hutton Theory of the Earth Published in the late 1700s Uniformitarianism Fundamental principle of geology "The present is the key to the past" Modern Geology Huttons Unconformity Relative vs. Radiometric Ages Relative Age determining when a geologic feature formed relative to other geologic features (cross cutting relationships, etc.) Radiometric Age determining when a geologic event occurred in exact units of time Determining Geologic Time Relative Dating Placing rocks and events in sequence Principles and rules of Law of superposition oldest rocks are on the bottom Principle of original horizontality sediment is deposited horizontally Principle of cross-cutting relationships younger feature cuts through an older feature Law of Superposition in any sequence of layered rocks the youngest stratum is at the top and the oldest stratum is at the base of the sequence (i.e. each bed is younger than the bed below it but older than the bed above it) Young Old Law of Superposition Original Horizontality all sedimentary rocks and lava are originally deposited in horizontal layers Cross Cutting Relationships any geologic feature that cuts across another geologic feature must be younger than the feature it cuts across younger older Figure 11.5 Relative Dating Principles and rules of Inclusions one rock contained within another (rock containing the inclusions is younger) Unconformities An unconformity is a break in the rock record Inclusions...
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This note was uploaded on 01/26/2012 for the course EAS 2600 taught by Professor Ingalls during the Fall '08 term at Georgia Institute of Technology.

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Lecture 18 - Geologic Time - Lecture 18 Geologic Time Exam...

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