Relative Dating & Deforming the Earths Crust
Folds, Faults and Deformities OH MY!! Is this the correct
principle?
Uniformitarianism Geologic processes that occurred in the past
canbe explained by current geologic processes Erosion and
weathering that happens today musthave been the same millions of
years ago Very slow, gradual, predictable process Is this the
correct principle? Why was this the accepted principle?
Catastrophism Geologic change happens suddenly Mountains, canyons
and oceans formed during rareevents These rare events are called
catastrophes Up until the mid-1800s, this was the acceptedprinciple
Why was this the accepted principle? Modern Geology
Uniformitarianism Catastrophism
Can geologic processes take a very long time?(think Tectonic
Plates, mountains growing) YES! Mountains forming/growing Grand
Canyon forming from erosion Moving of the continents Can events
happen very quickly? (Think meteor causing dinosaur extinction)
Large Volcanic eruptions forming islands and causing extinctions
Meteor strikes creating craters and causing extinctions
Earthquakes, Tsunamis, etc Relative Dating Relative Dating a method
used to determinewhether an object or event is older or younger
thananother object or event Who is Older or Younger? Absolute
Dating Absolute Dating any method used to determinethe age of an
event or object in numbers Certain molecules called Isotopes decay
over time Isotope An atom that has the same number ofprotons, but a
different number of neutrons We can use this decay to measure how
old somethingis (rocks, fossils, etc) Half-life the amount of time
it takes for half of aradioactive substance to decay Disturbances
Unfortunately not all rock layers are laid outperfectly. Some
things that can make things moredifficult are Unconformity missing
part of a geologic column Missing rock layer(s) due to either
Erosion or Non- deposition Deformations Altering of rock layers
after theyare laid down, but not removing them Deformations
Deformations Tectonic plates move, causing stress to build up inthe
lithosphere Stress = force (three types) Compression = squeeze
together Tension = stretch apart Shearing = sliding past Stress
from tectonic plates cause rock layers in thelithosphere to change
Folding Definition: bending rock layers due to stress
Older rock starts on bottom Anticline = upward arch (looks like an
A) Syncline = downward, U shaped (think sink) SYNCLINEANTICLINE
Folding Folds can be large or small
Some measured inkilometers orcentimeters MONOCLINE Faults
Definition: surface along which rocks break andslide past each
other Can be seen on the earths surface Usually have a Hanging wall
and Footwall Type of Stress? Which wall falls down? Are rock layers
disturbed? Type of Stress? Which wall falls down? Are rock layers
disturbed? Type of Stress? Which wall falls down? Are rock layers
disturbed? Rock layers arent always perfect
Relative Dating Faults, Unconformities and Deformations raise avery
important problem Rock layers arent always perfect So what do we do
when rock layers arent perfect? What happens when they look more
like This. How do we find Relative Age? Relative Dating One way
scientists calculate relative age is by usinga set of rules
Superposition if undisturbed, rock layers willalways be older as
you go down (youngest on top) Original Horizontality Layers of rock
are alwaysformed in relatively even horizontal layers Cross-Cutting
Rule if there is a fault cutting throughlayers of rock, the rock
must be older Deformation Rule if there is a deformation
(fold,tilt, intrusion) the rock that is deformed must be older How
do we find Relative Age? Relative Dating Another way geologists can
figure out disturbedlayers of rock is with the Geologic Column
Geologic Column a complete set of the rock layerswith all known
fossils and layers in their proper order Geologic Columns are used
to find Unconformities When a layer of rock is missing from Erosion
or Non- Deposition the geologic column can tell geologistswhat
SHOULD be there Which layers are missing from the second
outcropping?
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