Sir Charles Lyell
Time and Geology
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).
present is the key to the past…”
•
“The
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
Sedimentary Deposition
Intrusion
Tilting & Erosion
Subsidence and New Marine Deposition
Missing Formation
Dike Event
Erosion and Exposure
Subsidence & Deposition
Fluvial Deposition
Complex Subsurface Geology
Contact Relations