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Trilobite. James Hutton- The first Geologist!. Time and Geology. Sir Charles Lyell. Image source: www.mnsu.edu/emuseum. The Key to the Past. Relative Time- “this rock is older than that” Principles Used to Determine Relative Age Unconformities Correlation
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James Hutton- The first Geologist!
Time and Geology Sir Charles Lyell Image source: www.mnsu.edu/emuseum
The Key to the Past Relative Time- “this rock is older than that” Principles Used to Determine Relative Age • Unconformities • Correlation • The Standard Geologic Time Scale • Index Fossils Absolute Time- “this rock is 28 million years old” Principles of radioactive decay • Instruments • The age of the Earth
Important Figures in Geologic Time • James Hutton (1726-1797): Native of Edinburgh, Scotland. Father of modern Geology. Published “Theory of the Earth” in 1785 in which he outlined that geological features and ancient rocks could be explained by present-day physical and chemical processes. • Charles Lyell (1797-1875): Rebelled against prevailing thought, which was rooted in Biblical interpretation and Catastrophism. His main contribution was the development of Uniformitarianism (Actualism). “The present is the key to the past…” • Modern view holds that processes that operate today have shaped the Earth through Geological Time, but rates may not have always remained constant.
Important Relative Age Dating Principles • Original Horizontality: all beds originally deposited in water formed close to horizontal
Superposition: within a sequence of undisturbed sedimentary or volcanic rocks, layers become younger, upward
Lateral Continuity: original sedimentary layers extend laterally until it thins out at edges rocks that are otherwise similar, but are now separated by a valley or other erosional feature, can be assumed to be originally continuous.
Cross-cutting Relationships: disruptions in any rock sequence occurred after the youngest established event in the undisturbed sequence Ie. A rock or fault is younger than any rock (or fault) through which it cuts