Transcript Rock Sequencing ppt review

Earth’s
History
But…there is no book!
Oh…rats…
Why do we want to know Earth’s
History?
• Catastrophic Events
– If it has happened before, can it happen again?
• Environmental/Climate Changes
– Global Warming?
• Earthquake activity
– Where are the active earthquake areas?
• Building Project Safety
– Where can we build our homes without them being destroyed?
• General Curiosity
***All this to help us understand how our planet
got the way it is, and where it might be headed.
So that we can be prepared…
How does Earth “write” its history?
All sediment begin
somewhere else from
where we usually find it
Erosion = Eraser
Deposition = Deposits
= Writing History
Igneous
Intrusion
= Writing
Eroded sediments end
Up somewhere else
Deposited in layers
MainQ:
Concept:
We
can
use
layers
of
sediment
to
How do we see Earth’s
determine whathistory?
the area used to be like and
There are at least three
different
layers
in this picture:
even figure out what
has
happened
in the area over periods of time.
A: Strata
Stacked layers of rock and
soil.
Each layer is made of slightly
different stuff which make
them look just a bit different:
Normally, the layers are found flat
And horizontal Like these
But sometimes they can be tilted like these
or even have their order totally
mixed up as we will see!
Horizontal Layers in a Depositional
Environment
Layers of Sediment are deposited one upon the other. Clearly
The layers on the bottom were deposited first.
Body of Water
Sedimentary Rock
Layers
More examples of strata:
Colorful strata near
Capitol Reef National Park
Can you see
the fold?
You can see that there are
Sandstone with folded layers
many different layers
made of the exact same
in this picture
material
Originally these layers were flat and horizontal but now they
Are folded and tilted…but they did start out flat
Horizontal Layers can get squished (they
won’t look horizontal anymore):
Mountain / Erosion
Body of Water
squeezing
squeezing
You can see the folds caused by tectonic forces
squeezing the layers of strata
Strata is often messed up some and can be a bit hard to “read”
Q: How to tell the age of rock:
A: Superposition
• Means: one thing
placed upon another
The youngest (age) layer
is on top!
• Geologic Example:
Layers of rock
stacked by
Deposition.
The cooled lava has formed a new rock
layer on top of the sandstone that
was already there
How to tell the age of rock:
Relative Dating
This is not an exact method.
It does not give an exact year!
*Used to find the age of a fossil or rock compared to
others!
A) Comparing Strata Locations
B) Index fossils
*If a particular species lived
only in a certain time period
then you know that whatever
layer you find its fossil, that
layer is the same age
as the fossil
Comparing strata
locations:
• Notice that what you see
on one side of the
stream, you also see on
the other side of the
stream.
We figure that even though they are
not connected anymore, the layers on
either side of the river are the same!
The layers used to be connected,
but the river has cut them in half!
But we still understand that the layers are the same age!
Originally the layers continued all the way through:
• If you find one layer in one place and you find
the same layer on the other side of the river – it’s
probably gonna be the same layer of sediments.
River
The layers were deposited
In a shallow sea, but the sea
Dried up and a river cut part
Of the layers away
Index Fossils
• Each fossil shown here is
only found in the
particular age that is
shown:
• We know how long ago
these time periods are:
• If you find one of these
fossils in a layer of strata,
you know when it lived
and how old that layer of
strata is!
Any layer of strata we find this particular fossil
in we know must have been deposited in the Jurassic Period
which was years ago…
Where is the index fossil?
The layers of strata are
numbered along this side
The types of fossils
Are indicated here
Find the layer with
fossils that only
appears once
Here it is!!!
***The yellow spiral shell fossil only appears
in this single layer. If we know when this
critter lived, when know exactly when this
layer was deposited! And we can make
estimates of when the layers above and below
were deposited as well!
Why are layers sometimes “messed up”:
Can you match up the layers?
The soil and rock between these 3 locations has been eroded away.
Fill in the empty spaces:
Notice that layer D is totally missing in location 2
Something has caused this layer to disappear between location 2 and 4
There are two index fossils indicated here as well. They help
Us match the layers together!
Why are layers sometimes “messed up”:
Volcanic “Intrusion” Example:
“Intrusion” means that magma has
cut it’s way through other layers that
were already there! Now it has become igneous rock:
You can see the sandstone layers
That were already present (old)
This diagonal layer of
volcanic rock cut it’s way
through As magma after the sandstone
was already there (young).
Why are layers sometimes “messed up”:
Faulting and Folding
• Earthquake events can mix layers up
and put them totally out of order.
Top
Bottom
The layers are
getting separated
The fold has caused what
should be the bottom
To become the top
15 don’t forget the tree!
14
Imperfections in the Strata
13
Q: Can you follow the order?
There
are 15 events/features
Sometimes
the strata
Try to predict which layer is
difficult
tobefore
read!
Next in the
sequence
You click the button!
is
10
9
7
2
5
Tilting=6
3
12? Hard to be sure… 4
11
8
1