Download 6.1 & 6.2 Rock & Fossil Record

Earth’s Story
6.1 & 6.2
1788
 James Hutton
 Theory of the Earth
 Uniformitarianism
Uniformitarianism
 Present is the key to the past
Main concepts of uniformitarianism:
 Geologic processes we see now were active
in the past.
 The physical, chemical & biological laws that
operate today have operated throughout
Earth’s history. (Earth Science, Tarbuck…)
 Earth’s physical features were formed by
these same processes over long periods of
time.
1830s
 Charles Lyell
 Reintroduced uniformitarianism
 Now widely accepted by scientists
Catastrophes
 Occasionally occur
 Example:


65 mya asteroid hit Earth
Dinosaur extinction
Homework
 Read pages 152 - 155
Paleontology
 Study of past life
 paleobotanists
6.2
 Relative Dating: Which Came First?
Law of Superposition
 Younger rocks lie above older rocks
 http://www.classzone.com/books/earth_scien
ce/terc/content/investigations/es2903/es2903
page03.cfm
Principle of Original Horizontality
 Sediments are deposited horizontally.
 So…if we see beds of sedimentary rock that
are folded or tilted, they were deformed after
deposition.
 http://www.classzone.com/books/earth_scien
ce/terc/content/investigations/es2903/es2903
page04.cfm
Law of Cross-cutting Relationships
 An igneous intrusion is younger than the
layers which it cuts.
 http://www.classzone.com/books/earth_scien
ce/terc/content/investigations/es2903/es2903
page08.cfm
Law of Cross-cutting relationships
 If a fault or intrusive
rock cuts through other
rocks, then it is
younger.
http://www.earthscienceworld.org/images/search/results.html?Keyword=Cross-Cutting
Law of lava flows
 A lava flow is younger than the layers which it
covers.
What Can Cause Disturbances?
 Folding
 Faulting
 Intrusion
 Erosion
Inclusions
 When one rock has pieces of another
included in it
 The rock containing the inclusions is younger.
What Do We See?
 Unconformity

Break in geologic record



Erosion
Lack of deposition
Can represent long or short time period
Unconformities
 Disconformity
 Nonconformity
 Angular Unconformity
Disconformity
 Part of sequence of parallel rock layers is
missing
Disconformity
at which about one million years of stratigraphic record is missing, near
Gladeville in central Tennessee, U.S.A.,
Nonconformity
 Sedimentary rock layers lie on top of eroded
surface of nonlayered igneous or
metamorphic rock
Nonconformity
space-shuttle views of the Sinai Peninsula
Angular Unconformity
 Horizontal layers found on tilted or folded
rocks
Angular Unconformity
northern Utah
Other photos of unconformities
 http://www.earthscienceworld.org/images/sea
rch/results.html?Keyword=Cross%20Sections
Homework
 Read pages 156 - 161
Output
 Draw a geologic column block diagram.
 Show an:




At least 3 sedimentary layers
Angular unconformity
Igneous inclusion
List the relative ages from oldest to youngest.