EARTH 7 Lecture Notes - Lecture 3: Nicolas Steno, James Hutton, Siccar Point
Age Determination:
Relative dating - the age of rocks compared to other rocks
Absolute Dating: the age of rocks in years
Geologic timescale provides relative and absolute age information simultaneously
Relative Dating Principles:
- 1st 3 established by Nicolas Steno
1. Original Horizontality (get deposited horizontally, layer after layer of horizontal
deposition)
2. Lateral Continuity (rocks once continuous across barrier/span, since then, canyon
carved out, etc.
3. Superposition (the higher we go in rock column, the younger and younger we go)
James Hutton (1726-1797)
- Deep time: “...no vestige of a beginning, no prospect of an end.”
- Uniformitarianism: the present is the key to the past
- Began to see and convince people that earth must be very old
Uniformitarianism:
- Physical processes observed today operated in the geological past
- Slow processes acting over immense time have helped shape Earth’s surface
- Modern processes help us unravel ancient events
Since Hutton’s time, we’ve also learned about the importance of some fast and sudden
processes
4. Cross cutting Relationships (and Erosional Contact)
a. A rock unit is older than any feature that cuts or disrupts it
Erosional contact (unconformity): Siccar Point
- Vertical beds of Silurian sandstone (~425 Ma)
- Overlain by gently dipping Devonian redbeds (~325 Ma)
- Tons of missing time (~80 million years)
William Smith (1769-1839)
5. Faunal Succession
a. Fossils and Faunal Succession
i. Millions of organisms have evolved over time
ii. Each group of organisms lived during a discrete time interval
iii. This order is preserved in the rock record
iv. Thus fossils give us a sense of the relative ages of rocks
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Document Summary
Relative dating - the age of rocks compared to other rocks. Absolute dating: the age of rocks in years. Geologic timescale provides relative and absolute age information simultaneously. Deep time: no vestige of a beginning, no prospect of an end. Uniformitarianism: the present is the key to the past. Began to see and convince people that earth must be very old. Physical processes observed today operated in the geological past. Slow processes acting over immense time have helped shape earth"s surface. Modern processes help us unravel ancient events. Since hutton"s time, we"ve also learned about the importance of some fast and sudden processes. Cross cutting relationships (and erosional contact: a rock unit is older than any feature that cuts or disrupts it. Vertical beds of silurian sandstone (~425 ma) Overlain by gently dipping devonian redbeds (~325 ma) Tons of missing time (~80 million years) Faunal succession: fossils and faunal succession, millions of organisms have evolved over time.
