BP 6 Rates and scale of earth change are difficult to comprehend either too slow relative to human life or too huge in scale to imagine Related to how old we think the earth is Prior to late 18 ID: 469845
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Slide1
B.P. #5 Present state of earth is temporary - different in past, futureB.P. #6 Rates and scale of earth change are difficult to comprehend – either too slow relative to human life, or too huge in scale to imagine
Related to how old we think the earth is ----
Prior to late 18
th
century – earth = young; unchanging
1790’s on = earth processes the same as today; implies old earth
How old?? 4.55 billion years old Slide2
Implications of huge amount of time – (“deep time”)
Events that occur so slowly as to seem unimportant become important.
Given time, unlikely events WILL eventually occur. Slide3
B.P. #4 Materials move within each sphere and between spheres
Plate tectonic cycle Slide4
Cycling of Earth Materials – Plate tectonic cycleKEY TO HOW THE EARTH WORKS - NEW IDEA (1960’s)
Historical background –
What they knew in the early 1900’s
Continents and ocean floors – are different
Features of continents & forces that formed them
Continental drift – (1915) Alfred Wegener
Reaction to Wegener Slide5
Height
of the earth
’
s surface
-
B
A
What are the most common elevations of the earth
’
s surface?Slide6
Height
of the earth
’
s surface - the hypsographic curve
B
A
What are the most common elevations of the earth
’
s surface?
4-6 km below sea level, 0-1 km above sea levelSlide7
How does this fit with Big Points from last week?
What is the elevation of the ocean crust relative to the continental
crust?
Why
is the ocean water where it is?
What is the density of the ocean crust relative to continental crust?Slide8
What is the elevation of the ocean crust relative to the continental
crust?
Lower
Why
is the ocean water where it is?
Water fills in low areas
What is the density of the ocean crust relative to continental crust?
Ocean crust is more dense than continental crust - lower
How does this fit with Big Points from last week?Slide9
Cycling of Earth Materials – Plate tectonic cycleKEY TO HOW THE EARTH WORKS - NEW IDEA (1960’s)
Historical background –
What they knew in the early 1900’s
Continents and ocean floors –different crusts
Features of continents & forces that formed them
Continental drift – (1915) Alfred Wegener
Reaction to Wegener Slide10
1. Folded Mountains Slide11Slide12Slide13
Appalachian MtnsSlide14
When layers of rocks are laid down - they are horizontalSlide15
rocks in folded
mountainsSlide16
What has happened to the rocks in folded mountains?
Folded - not horizontal
What force caused this?
yieldsSlide17
What has happened to the rocks in folded mountains?
Folded - not horizontal
What force caused this?
yields
Compression - Slide18Slide19
Folded mountains, PennsylvaniaSlide20
Folded mountains, PennsylvaniaSlide21
2.
Rift systemsSlide22
b. Rift systems -
Sea level
Side view
How can a valley be formed
that is below sea level?Slide23
2. Rift systems -
Sea level
Side view
How can a valley be formed
that is below sea level?
Not by river erosion - rivers run to
ocean.. Are not lower than sea level.
Force? Slide24
2. Rift systems -
Sea level
Side view
How can a valley be formed
that is below sea level?
Not by river erosion - rivers run to
ocean.. Are not lower than sea level.
Force?
TensionSlide25
Rift valley - water can
’
t drain to ocean (why?) and so
evaporates leaving white salts (Death Valley, CA) Slide26
Basin and Range from space, rift system - forces?
x
X
= Death Valley area of previous slideSlide27
~Canada
~central US
This is a cross-section view.
3.
craton
Slide28Slide29
~Canada
~central US
This is a cross-section view.Slide30
Red = Canadian shieldSlide31Slide32
Questions about shield:
-- Where were these rocks formed - folded not broken?
-- How did they get to the surface?
-- Why are they so old?
-- Where do they go to find the oldest rocks on earth?
-- Where is ours?
Slide33
Questions about shield:
-- Where were these rocks formed - folded not broken?
Deep in earth
-- How did they get to the surface?
-- Why are they so old?
-- Where do they go to find the oldest rocks on earth?
-- Where is ours?
Slide34
Questions about shield:
-- Where were these rocks formed - folded not broken?
Deep in earth
-- How did they get to the surface?
Overlying miles of rocks were eroded…
then pushed up… isostasy
-- Why are they so old?
-- Where do they go to find the oldest rocks on earth?
-- Where is ours? Slide35
Questions about shield:
-- Where were these rocks formed - folded not broken?
-- How did they get to the surface?
-- Why are they so old?
Takes long time for erosion and uplift..
-- Where do they go to find the oldest rocks on earth?
-- Where is ours?
Slide36
Questions about shield:
-- Where were these rocks formed - folded not broken?
-- How did they get to the surface?
-- Why are they so old?
Takes long time for erosion and uplift..
-- Where do they go to find the oldest rocks on earth?
Shields -- there is a shield on every continent
-- Where is ours?
Slide37
Questions about shield:
-- Where were these rocks formed - folded not broken?
-- How did they get to the surface?
-- Why are they so old?
Takes long time for erosion and uplift..
-- Where do they go to find the oldest rocks on earth?
Shields -- there is a shield on every continent
-- Where is ours?
In Canada - northern MI, north NYSlide38
~Canada
~central US
This is a cross-section view.
c. Craton - 2nd part = stable platform(covered shield)Slide39
Nashville - covered shield - horizontal sedimentary rocksSlide40
Covered
Shield =
Blue, yellow
Green Slide41Slide42
Covered shield (platform) - note horizontal layersSlide43
Cycling of Earth Materials – Plate tectonic cycleKEY TO HOW THE EARTH WORKS - NEW IDEA (1960’s)
Historical background –
What they knew in the early 1900’s
Continents and ocean floors –different crusts
Features of continents & forces that formed them
Continental drift – (1915) Alfred Wegener
Reaction to Wegener Slide44
Wegener
’
s lines of evidence that continents drifted
1. Fit
of the continents
Slide45Slide46
~4 km thick Pm-J continental deposit
s
2. Similar sequence of rocks on all southern continentsSlide47Slide48
3. Similar fossils on all southern continentsSlide49
Without hair?
Lystrosaurus
With hair?