Relative Dating Powerpoint

Sir Charles Lyell
Time and Geology
Image source:
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
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…”
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
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
Tilting & Erosion
Subsidence and New Marine Deposition
Missing Formation
Dike Event
Erosion and Exposure
Subsidence & Deposition
Fluvial Deposition
Complex Subsurface Geology
Contact Relations