Download Geology

Geology
A Peak at Earth’s History
The Key to the Past is the Present
• Uniformitarianism
– is the assumption that the natural processes
operating in the past are the same as those
that can be observed operating in the present
– What does it Mean?
• By looking at the processes that are going on
today we can get an idea of what happened in the
past
Volcanoes
• Today we can observe a volcano erupt
lava, that lava forms black rocks called
Basalt
– When we find basalt, we can assume it was
formed by cooling lava
Erosion and sediments
• Today we can
observe erosion by
water, carrying
sediment down
stream, down cutting
canyons and arroyos.
• We can see the soil
and sediments being
deposited down
stream when the
water slows down.
Sediments
• Larger particles will be
•
dropped from the water first,
smaller particles stay
suspended in the stream,
until it slows down. Sand is
deposited on the inside of
stream bends.
• When we find narrow
sections of sandstone, we
might determine they were
deposited along a stream
channel
Deltas
• In Deltas where rivers
carry sediments into
lakes and oceans we
see this pattern
– Sand closest to shore
– Then silt
– Then the smallest
particles of clay
Ripples & Mud cracks
• We can see ripples in the
sediments on the bottoms
of lakes and ponds
caused by the waves
• We can assume was
rocks with ripples formed
under water
• We see Mud Cracks
when wet soil drys out
• We can assume rocks
with cracks were formed
after an area dried out
Mud Cracks
• Recent mud Cracks (Below)
• Fossilized Mud Cracks
Limestone
• Limestone is formed when marine
organisms deposit their calcium carbonate
shells or microscopic tests on the bottom
of the ocean
• When we see limestone
today we can assume
that it was formed
under the ocean.
Sandia Limestone 
Stratigraphy
• Okay, if you are like me, your desk piles up with
papers over the course of a day or week.
• The papers that were there first are on the
bottom and the newest papers are on top
• OR you go to the grocery store and you throw a
bunch of food in your cart and fill it up. The stuff
on the bottom would be from the first isle you go
down and the stuff on the bottom would be from
the first isle.
Stratigraphy
• Sedimentary rocks from in the same
way.
• Oldest layer are on the bottom, and
the youngest layers are on top…
• Ever been to the Grand Canyon?
• Oldest rocks are along the bottom,
youngest rock are on top
• Unless some thing happens to
disturb them…
Like a meteor impact
• Meteor crater in AZ
• Some layers of strata
Were flipped during the
impact
Erosion
• Layers can be eroded away….
• Leaving “Gaps” in the geological record
• Imagine if a
volcano erupted
and dropped a
layer of ash on
this outcrop in the
Painted Desert
(AZ)
Grand Canyon
• Oldest layer are on the
bottom
• Youngest layers are on
top
• Can tell relative age by
position
• ie which is older, which is
younger
• Can not tell absolute or
exact age by position
Index fossils
• Organisms
that were
short lived
in geologic
time make
good index
fossils
• Used to
help age
sediments
Absolute dating
Radiometric dating
• Certain elements
give off neutrons at
a certain rate
called a half-life
• By comparing the
ratios of the parent
element to the
Daughter product
we can determine
a rock’s absolute
age