Uniformitarianism
1.
Geologic processes that occurred in the past can be explained
___________________________________________________________________________________________ a.
Erosion and weathering that happens today must have been the same millions of years ago b.
Very slow, gradual, predictable process
Catastrophism
1.
_____________________________________________________________________________ a.
Mountains, canyons and oceans formed during rare events b.
These rare events are called catastrophes
2.
Up until the mid-1800’s, this was the accepted principle
Relative Dating
1.
Relative Dating – a method used to determine whether an object or event ______________________________
_______________________________________________________________
Absolute Dating
1.
Absolute Dating – any method used to determine the _______________________________________________
 Certain molecules called Isotopes decay over time
 Isotope – An atom that has the same number of protons, _________________________
________________________________________________________________________
 We can use this decay to measure how old something is (rocks, fossils, etc…)
 Half-life – the amount of time it takes for half of a radioactive substance to decay
Disturbances
 Unfortunately not all rock layers are laid out perfectly. Some things that can make things more difficult are…
1.
Unconformity – _______________________________________________________________________ a.
Missing rock layer(s) due to either Erosion or Non-deposition
2.
Deformations – Altering of rock layers after they are laid down, _________________________________
Deformations
 Tectonic plates move, causing stress to build up in the lithosphere a.
Stress = force (three types)
1.
Compression =
2.
Tension =
3.
Shearing =
 Stress from tectonic plates cause rock layers in the lithosphere to change

Folding
Definition: _____________________________________________________________ a) Older rock starts on bottom
Anticline =
Syncline =
 Folds can be large or small
 Some measured in kilometers or centimeters
Faults
Definition: surface along which rocks break and slide past each other
 Can be seen on the earth’s surface
 Usually have a ___________________________________________________
 Faults, Unconformities and Deformations raise a very important problem…
Rock layers aren’t always perfect
 So what do we do when rock layers aren’t perfect?
How do we find Relative Age?
 One way scientists calculate relative age is by using a set of rules
1.
Superposition – if undisturbed, rock layers will always be older as you go down (youngest on top)
2.
Original Horizontality – Layers of rock are always formed in relatively even horizontal layers
3.
Cross-Cutting Rule – _________________________________________________________________
__________________________________________________________________________________
4.
Deformation Rule – _________________________________________________________________
__________________________________________________________________________________
 Another way geologists can figure out disturbed layers of rock is with the Geologic Column
 Geologic Column – a complete set of the rock layers with all known fossils and layers in their proper order
 Geologic Columns are used to find _____________________________
 When a layer of rock is missing from Erosion or Non-Deposition ________________
____________________________________________________________________