Historical notes
Catastrophism
Landscape developed by catastrophes
James Ussher, mid - 1600s, concluded Earth was only a few thousand years old
Modern geology
Uniformitarianism
Fundamental principle of geology
"The present is the key to the past."
James Hutton
Theory of the Earth
Late 1700s
Sir Charles Lyell
Advanced modern geology
Principles of Geology
Mid-1800s
Relative dating
Placing rocks and events in sequence
Principles and rules of
Law of superposition
Principle of oringial horizontality
Principle of cross-cutting relationships
Inclusions
Unconformities
Law of superposition
Oldest rocks are on the bottom
Principle of original horizontality
Sediment is deposited horizontally
Inclusions
One rock contained with in another - rock containing the inclusions is younger
Unconformities
An unconformity is a break in the rock record
Types of unconformities
Angular unconformity - tilted rocks are overlain by fly-lying rocks
disconformity - strata on either are parallel
nonconformity
metamorphic or igneous rocks below
younger sedimentary rocks above
Correlation of rock layers
Matching rocks of similar age in different regions
Often relies upon fossils
Fossils
Remains or traces of prehistoric life
Types of fossils
Petrified - cavities and pores are filled with precipitated mineral matter
Formed by replacement - cell material is removed and replaced with mineral matter
Mold - shell or other structure is buried and then dissolved by underground water
Cast - hollow space of a mold is filled with mineral matter
More types of fossils
Carbonization - organic matter becomes a thin residue of carbon
Impression - replica of the fossils surface preserved in fine-grained sediment
Preservation in amber - hardened resin of ancient trees surrounds an organism
Indirect evidence includes
Tracks
Burrows
Coprolites - fossils dung and stomach contents
Gastroliths - stomach stones used to grind food by some extinct reptiles
Conditions favoring preservation
Rapid burial
Possession of hard parts
Fossils and correlation
Principle of fossil succession
Fossils succeed one another in a definite and determinable order
Proposed by William Smith - late 1700s and early 1800s
Index fossils
Widespread geographically
Existed for a short range of geologic time