GEO103K – GEOLOGY – UNDERLYING PRINCIPLES with key
Name: _________________________________
Geology is the science of the history of Earth as told through the evidence of
rocks.
Why is the study of rocks important?
Rocks record geological events and changing life forms of the past.
Nicholas Steno (1638 to 1686)
Nicholas Steno was a Danish Roman Catholic bishop who observed layers in the Earth
and fossils in those layers. His principles are the foundation of modern geology and
paleontology.
What is paleontology? The earth science that deals with fossil organisms and
related remains.
Youtube The most groundbreaking scientist you've never heard of
https://www.youtube.com/watch?v=If4I3aF1PRg
Youtube Steno’s Law
https://www.youtube.com/watch?v=46ctHq1RzaU
Steno’s Four Laws:
 Original Horizontality
 Superposition
 Faunal Succession
 Cross-Cutting Relationships
Nicholas Steno and Original Horizontality (1636-1686)
This principle states that layers of sediment are originally deposited horizontally
under the action of gravity. The principle is important to the analysis of folded and
tilted strata.
Nicholas Steno and Superposition (1636-1686)
Superposition states that in an undeformed sequence of sedimentary rocks, the oldest
layers (strata) are on the bottom, and the youngest strata is on the top.
Nicholas Steno and Cross-Cutting Relationships (1636-1686)
When a fault cuts through rock layers (strata) or when magma intrudes into rock from
below, the faults and intrusions are younger than the rock.
Unconformities - breaks in the geological record
A long period of time is which normal deposition stops and erosion takes over, then
deposition resumes.
An angular unconformity is a period of time in which deformation (folding/tilting) has
taken place.
James Hutton – the Father of Modern Geology
In the late 1700’s James Hutton observed an unconformity at Siccar Point in his
native Scotland. He made two extraordinary conclusions based on his
observations.
Youtube Hutton's Uncomformity (BBC Earth Story)
https://www.youtube.com/watch?v=lMfPSdrrjZI

His 1st conclusion is called uniformitarianism. Uniformitarianism means that the
forces and processes that we observe today have been at work for all the Earth’s
history. If we understand today’s geologic forces we can understand how the Earth
was formed and continually reformed. The concise way of stating
uniformitarianism is
The present is the key to the past.

His 2nd conclusion was
The Earth must be very old.
READING ASSIGNMENT- SECTION 12.2
Page 343 – What are fossils?
What three things can fossils tell us?
What determines the type of fossil?
What are the three types of fossil? (Hint the 3 blue sub-paragraph
headers)