Announcements I will be writing PS #1 over the weekend, and posting it by Monday… It will be due Feb 9 th .
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Announcements
I will be writing PS #1 over the weekend, and posting it by
Monday… It will be due Feb 9th.
Clarification: The angle of Earth’s tilt does not change
during the year!
Views of the Earth from the Sun’s perspective
It only looks that way from the sun’s frame of
reference.
The axis is always parallel to itself.
Quiz 2!
2. Sun Angle: insolation curves
2. Sun Angle: insolation curves
WinterWinter
SummerSummer
Autum
n
Autum
nSpr
ing
Spr
ing
WinterWinter
Insolation
23.5o axis tilt
0o axis tilt
An Equation for the Sun Angle
On an equinox
Declination = 0°
An Equation for the Sun Angle
On an equinox
Declination = 0°
At the equatorLat =Sun angle =
0°90°
An Equation for the Sun Angle
On an equinox
Declination = 0°
At the north poleLat =Sun angle =
90°N0°
An Equation for the Sun Angle
On an equinox
Declination = 0°
At some latitude xLat =Sun angle =
x°N90°- x°
x° 90°- x°
But then we have to adjust for declination!
Equator is sub-solar point
North pole tilted toward the sun
North pole tilted away from the sun
Equator is sub-solar point
Summer
Winter
Fall
Spring
But then we have to adjust for declination!
Sun Angle = 90°-x°
Sun Angle = 90°-x°
Sun Angle = 90°-x°-23.5°
Sun Angle = 90°-x°+23.5°Summer
Winter
Fall
Spring
Final Formula
Sun Angle at Noon =
90° - Latitude° + declination°
Summer
Note: this formula is for the angle with the southern horizon, so it makes the most sense to only use it in the Northern Hemisphere
Lithosphere: solid Earth
Geologic time: dating2 types2. Relative Dating = sequential age
- based on positions of rocks relative to each other
- e.g., rock layer B is older than A and younger than C
2. Absolute Dating = actual age- based on radiometric dating- e.g., rock layer B is 50 million years
old
Dating using Geological Laws
1. Law of superposition- younger rocks are deposited on top of older
rocks
younger
young
oldest
older
old
Grand Canyon Layers
1. Law of original horizontality- sedimentary rocks & lava are originally laid
down horizontally
Roughly horizontal
Dating using Geological Laws
A roadcut photo that I stole… WV maybe?
1. Law of cross-cutting relations- rocks that intrude into other rocks are younger
than their host rocks - faults are younger than the rocks they cut
through- folds are younger than the rocks they bend
Dating using Geological Laws
Roadcut near Moab, UT
A
BC
D
Events:A depositedB depositedC depositedD depositedFaultingErosion of Surface XErosion of Canyon
But in what order?
Order of Events:D depositedC depositedB depositedFaultingErosion of Surface XA depositedErosion of Canyon
X
Events:A depositedB depositedC depositedD depositedE depositedF depositedG depositedFoldingErosion of Surface X
Order of Events:G depositedF depositedE depositedD depositedC depositedFoldingErosion of Surface XB depositedA deposited
AB
CD
X
EF G
Events:A depositedB depositedC depositedD depositedE depositedF depositedFoldingFaultingErosion of Surface XErosion of Surface Y
Order of Events:F depositedE depositedD depositedC depositedFoldingErosion of Surface YB depositedFaultingErosion of Surface XA deposited
A
BC
D
X
EF
Y
Events:Cooling of Granite ADeposition of Sandstones B, E, & IDeposition of Shales C & HDeposition of Limestone D & FCooling of Basalt G Folding (Tilting)FaultingErosion of surfaces X, Y, ZFormation of mesa
Order of Events:1 . A 9 . E2 . X 10 . F3 . B 11 . Z4 . C 12 . G5 . D 13 . H6 . fold/tilt 14 . I7 . Y 15 . mesa8 . fault
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