Transcript Lab #13: Geologic Profiles - High School of Language and

Lab #13: Geologic Profiles
February 11th, 2014
What Is Deposition?
• Is the process in which sediments (small
pieces of rock) are added to a to a landform,
or the bottom of a lake/ocean
• This can be done by water, wind, or glaciers
What is Stratigraphy?
• Strata are layers that are
found in the Earth’s
surface
• Stratigraphy is the study
of Earth’s layers
Four Laws of Stratigraphy
• Law of Original Horizontality: Sedimentary
rocks are almost always deposited in
horizontal layers
• Why do you think so?
Four Laws of Stratigraphy
• Law of Superposition of Strata: Oldest rock
layers can be found at the bottom of an
undisturbed bed
Four Laws of Stratigraphy
• Law of Cross Cutting Relationships: A rock is
always older than the process that affects it;
rock strata are older than the faults or the
magma intrusions that cut through them.
Law of Uniformitarianism
• The processes that are currently shaping the
Earth have been the same processes since the
formation of the Earth “the present is the key
to the past”
• What we see today
MUST be what has
been happening for
millions and millions of
years!
Do Rocks Always Stay Horizontal?
• No!
• They can fold.
Do Rocks Always Stay Horizontal?
• They can tilt!
What is an Intrusion?
• When molten rock (magma) flows over an
older layer of rock
Unconformity
When weathering and erosion breaks apart rock and
leaves a missing part of the rock record.
Index Fossils
• Two things must be true about Index Fossils:
– 1: They lived for only a “short” period of time
– 2: They lived across a wide geographical area (they
lived almost everywhere in the world!