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.erosional
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