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# Lecture5 lawsofgeology

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### Transcript

• 1. Announcements I will be writing PS #1 over the weekend, and posting it by Monday… It will be due Feb 9 th .
• 2. 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 .
• 3. The axis is always parallel to itself.
• 4. Quiz 2!
• 5. 2. Sun Angle: insolation curves
• 6. 2. Sun Angle: insolation curves Winter Summer Autumn Spring Winter
• 7. Insolation 23.5 o axis tilt 0 o axis tilt
• 8. An Equation for the Sun Angle On an equinox Declination = 0 °
• 9. An Equation for the Sun Angle On an equinox Declination = 0 ° At the equator Lat = Sun angle = 0 ° 90 °
• 10. An Equation for the Sun Angle On an equinox Declination = 0 ° At the north pole Lat = Sun angle = 90 °N 0 °
• 11. An Equation for the Sun Angle On an equinox Declination = 0 ° At some latitude x Lat = Sun angle = x °N 90 °- x° x ° 90 °- x°
• 12. 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
• 13. 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
• 14. 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
• 15. Lithosphere: solid Earth
• 16. Geologic time: dating
• 2 types
• 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
• e.g., rock layer B is 50 million years old
• 17. Dating using Geological Laws
• Law of superposition
• - younger rocks are deposited on top of older rocks
younger young oldest older old
• 18. Grand Canyon Layers
• 19.
• Law of original horizontality
• - sedimentary rocks & lava are originally laid down horizontally
Roughly horizontal Dating using Geological Laws
• 20. A roadcut photo that I stole… WV maybe?
• 21.
• 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
• 22. Roadcut near Moab, UT
• 23. A B C D Events: A deposited B deposited C deposited D deposited Faulting Erosion of Surface X Erosion of Canyon But in what order? Order of Events: D deposited C deposited B deposited Faulting Erosion of Surface X A deposited Erosion of Canyon X
• 24. Events: A deposited B deposited C deposited D deposited E deposited F deposited G deposited Folding Erosion of Surface X Order of Events: G deposited F deposited E deposited D deposited C deposited Folding Erosion of Surface X B deposited A deposited A B C D X E F G
• 25. Events: A deposited B deposited C deposited D deposited E deposited F deposited Folding Faulting Erosion of Surface X Erosion of Surface Y Order of Events: F deposited E deposited D deposited C deposited Folding Erosion of Surface Y B deposited Faulting Erosion of Surface X A deposited A B C D X E F Y
• 26. Events: Cooling of Granite A Deposition of Sandstones B, E, & I Deposition of Shales C & H Deposition of Limestone D & F Cooling of Basalt G Folding (Tilting) Faulting Erosion of surfaces X, Y, Z Formation of mesa Order of Events: 1 . A 9 . E 2 . X 10 . F 3 . B 11 . Z 4 . C 12 . G 5 . D 13 . H 6 . fold/tilt 14 . I 7 . Y 15 . mesa 8 . fault