Geology 120 1
*Lecture 1 (1/19): Geologic Thinking
WHAT IS GEOLOGY?
-The geosciences: incorporates volcanism, climate change, Earth’s interior, microbiology, earth history, erosion and landscapes, atmosphere and geomicrobiology
-the study of how the earth change on a variety of scales across space and time (both short and long term, but most amazing changes are on long term scales)
-geology influences hazards, flooding, soil and water quality, mineral and energy resources as well as global change
Geology and Place
-How does geology affect Fort Collins?
-flats to the east and mountains to the west (sharp boundary)
-reservoirs (mostly man made)
-farmland to the east
-more rock exposure to the west
-Why does the landscape look the way it does?
-due to geologic processes like erosion and chemical weathering
-agriculture affecting the soil quality and formation in the east
-weather (storm systems, more rain on west and dry on east)
-What geologic processes are currently acting or have acted on the landscape? -erosion and weathering from rivers (also flooding)
-mountain formation (plate tectonics and fault lines)
-How do these processes affect your lives?
*Lecture 2 (1/21)
Death Valley CA Observations
-surrounded by mountains
-little to no rivers
-fairly flat in valley, but surrounded by steep mountains If you want to learn more check out How do you calculate a weighted mean?
Don't forget about the age old question of What are the requirements for a food label?
-dry, very little plant life and biodiversity
-rocky and rough, cracked terrain
-high winds that possibly move the rocks
Hypotheses for what caused the tracks next to the rocks:
-strong winds possibly moved the rocks
-combo of rain and wind
-pulled by magnetic field
Key things for good hypothesis
1. Has to be testable
2. Good to have multiple hypotheses
How do we test these hypotheses? What data should you collect?
-go out and record wind speeds
-set up cameras to check for animals
Geology 120 2
-measure precipitation levels (rain gauges)
-rock samples to see if any material in the rock is magnetic We also discuss several other topics like What happened in the chesapeake incident?
Qualitative v Quantitative Data
-Qualitative=non-numeric (descriptions, drawings…) We also discuss several other topics like Is sodium sulfide ionic?
-Quantitative=measurement with a specific numerical value
Observations of Upheaval Dome in Utah
-very steep, lots of mountains
-lots of rivers and canyons
Hypotheses for the Dome?
-rising salt (this happens when you have lots of evaporation that causes salt buildup) -rising magma
How to test these?
-measure salt levels in the rocks
-see how close the magma is to the surface, look for recent earthquake activity -test materials in the rock and compare to rocks around the dome
Geology=study of Earth’s interior and exterior surfaces, the rocks and other materials that are around us and the processes that have resulted in the formation of those materials, the water that flows over the surface and lies underground, the changes that have taken place over the vastness of geological time, and the changes that we can anticipate will take place in the near future. We also discuss several other topics like What is the difference between constrained and unconstrained optimization?
-is arguably the most integrated of all the sciences
-displayed on a grand scale, can be quick events or take place over billions of years Why Study Earth?
-we rely on it for valuable resources and we need to know how to get them and where they are and how to exploit them sustainably
-we can learn how and why earth is changing
-can use our knowledge to understand other planets
What do Geologists Do?
-ranges from working for resource industries or hazard assessment and mitigation, water supply planning, development and management…
-employed by private sectors or the gov
Minerals and Rocks
-Earth=made up of 90 naturally occurring elements that combine to make minerals -mineral=naturally occurring combo of specific elements that are arranged in a repeating 3D structure called a lattice
-halite for example is NaCl that alternates between Na and Cl at 90 degree angles -in nature, minerals are found in rocks and most rocks are made up of a few different minerals -granite is a common rock composed of many minerals
-rocks form in many ways:
1. Igneous rocks form from magma that has cooled slowly underground or cooled fast at the surface after a volcanic eruption (basalt for ex) Don't forget about the age old question of What was the dominant form of political organization?
2. Sedimentary rock like sandstone form when weathered products from other rocks accumulate at surface and buried by other sediments
Geology 120 3
3. Metamorphic rocks form when igneous of sedimentary rocks are heated and squeezed until the minerals are unstable and create diff rock (schist for ex) Mineral v Rock-mineral=pure substance with specific composition and structure whereas a rock is a mix of several diff minerals
Fundamentals of Plate Tectonics
-plate tectonics is the model or theory that is used to understand Earth’s development and structure
-core=made of mostly iron, outer core=hot enough for Iron to be liquid, inner core is even hotter but the pressure is so high that it is solid
-mantle made of iron and magnesium silicate minerals (bulk of mantle is solid rock but can flow slowly) surrounding the partially molten mantle (asthenosphere) is rigid -crust is made mostly of granite on continents and basalt in oceans
-crust and outer mantle makes up the lithosphere which is divided into 20 tectonic plates that move in diff directions on the surface
-important property of Earth is that temp increases with depth (called the geothermal gradient) -Heat is continuously flowing outward from
Earth’s interior, and the transfer of heat from
the core to the mantle causes convection in
the mantle and is driving force for plate
-At places where convection currents in the
mantle are moving upward, new lithosphere
forms (at ocean ridges), and the plates move
apart (diverge). Where two plates are
converging (and the convective flow is
downward), one plate will be subducted
(pushed down) into the mantle beneath the
other. Many of Earth’s major earthquakes and
volcanoes are associated with convergent boundaries
1. What is the evidence for plate tectonics?
-distribution of rocks and fossils
2. What constitutes a plate?
-a massive, irregularly shaped slab of solid rock, generally composed of both continental and oceanic lithosphere. Plate size can vary greatly, from a few hundred to thousands of kilometers across; the Pacific and Antarctic Plates are among the largest
3. What are the main differences between ocean crust and continental crust? -ocean crust is made of dense and heavy basaltic rocks and are thin crusts (~5km thick) -continental crust is made of lightweight minerals like quartz and feldspar and is thick (~100km) to support it’s elevation
4. What are the three main types of plate boundaries?
1. divergent (moving apart) boundaries are spreading boundaries where new oceanic crust is created from magma derived from partial melting the mantle caused by decompression s hot mantle rock from deep down is moved to surface. Most are located at oceanic ridges.
Geology 120 4
2. Convergent (moving together) boundaries-3 types
a. Ocean-ocean-one is pushed or subjected under the other (usually the denser or colder one) This causes a trench along the boundary
b. Ocean-continent-ocean plate pushed under continental
c. continent-continent-leads to mountain formation
3. Transform (moving side by side) Boundaries
*Lecture 3: Plate Tectonics (1/25)
What’s inside earth?
-upper layer is crust with 2 types:
1. Continental (thick)
2. Oceanic (dense and thin and composed of basalt)
-mantle is next and is the thickest layer and is denser than ocean crust
Geology 120 5
-deepest layer is the iron-nickel core which is very dense
Some layers are stronger than others
-lithosphere THIS IS THE PLATE AND IS STRONG (made of continental or oceanic crust and uppermost mantle)
-asthenosphere is weaker and hot and mostly solid
3 Types of Plate Boundaries
Divergent boundary between 2 ocean plates
ridge, location of earthquakes
-example=oceanic ridge in Atlantic, most divergent boundaries are in ocean -example of continental rift=Arabian Peninsula and Afar region spread apart by Red Sea Convergent Boundary Between Ocean and Continental Plate
-the density determines which plate will subduct (if it’s between 2 oceanic plates, the temperature determines the density and which plate subduct. The older or cooler=the denser) -2 continental plates very rarely subduct
Geology 120 6
-2 plates slide past each other
-usually link divergent boundaries
-ex=San Andreas fault where east moves north and west is moving south. This is linking convergent boundaries in north and divergent ones in south
-Earthquakes are found at ALL types of boundaries b/c rocks are under stress -Volcanoes are NOT USUALLY found at continental collision boundaries (like the Tibetan Plateau) b/c there is NO subduction in these cases! Also b/c the plateau is so high up and the crust is so thick and the magma can’t make it up to the surface.
What Happens to Create the Pacific Ring of Fire?
-Atlantic is getting bigger and Pacific is shrinking so subduction all around that -new ocean crust is created in Pacific which pushes older crust to continent and they subduct and cause volcanoes and earthquakes
-subduction belts beneath continental plates like the Andes
What type of plate boundaries are likely to have mountains?
*(1/28) Plate Tectonics Continued
5 Rules of Plate Tectonics
1. Plate boundaries either terminate against other boundaries or encircle the entire earth. Mature plate boundaries DO NOT simply end (although plate boundaries in the process of forming may be so indistinct as to appear that way)
2. The motion of a plate should be generally consistent throughout the extent of the plate. Plate motions can be described as ROTATIONS around axes that pass through the center of spherical Earth. Plates move as rigid blocks
3. Rate of crustal consumption (at convergent boundaries) must equal the rate of crustal creation (at divergent boundaries) at any given time, otherwise Earth would expand 4. Transform boundaries link diff boundary types and are only active where opposite sides of the transform and moving relative to e/o
5. In plate tectonics, EVERYTHING is in motion. The tectonic plates, and the plate boundaries that surround them are all moving relative to a fixed HOTSPOT REFERENCE FRAME. When describing plate motions, it is important to note the frame of reference being used SYMBOLS on a map: