Earth's Structure and Geologic Processes: Core, Mantle, Tectonics

1. Ch. 10 Notes APES: Mrs. Sealy

2. Structure of the earth • Core • Inner: solid, high temp and pressure, made of: nickel and iron • Outer: liquid, cooler than the inner core, Made of: nickel and iron • Mantle • Made of iron, oxygen and silicon (Rock called peridotite) • Solid at the bottom becomes more Pliable and plastic near the surface. • Upper layers: asthenosphere and the lithosphere • Crust • Thinnest zone (6 miles deep to 35 miles deep) • Mostly made of silicon and oxygen in the Form of quartz (SiO2) • Two types of crust: - oceanic-which is dense and made of basalt - continental crust Which is less dense and made of: granite

3. 35 km (21 mi.) avg., 1,200˚C Crust 100 km (60 mi.) 200 km (120 mi.) Low-velocity zone Crust Mantle Lithosphere Solid 10 to 65km 2,900km (1,800 mi.) 3,700˚C Asthenosphere (depth unknown) 100 km Outer core (liquid) 200 km Core 5,200 km (3,100 mi.), 4,300˚C Inner core (solid) Geologic Processes • Structure ofthe Earth Fig. 10.2, p. 212

4. Internal Earth Processes Plate tectonics: theory developed in the 1960’s about the crust of the earth. The theory says that the crust is not one large piece, but is broken into large segments called plates. When these plates move and collide they form:

5. Divergent Plate Boundary Divergent plate boundary: where plates move apart in opposite directions • Landforms: under water mountain chains called mid-ocean ridges, on land forms rift valleys • Examples: Mid-Atlantic Ridge, African Rift Valley, Iceland, Baja California

8. Convergent Plate Boundaries Convergent plate boundary: Where plates collide • Forms subduction zones where one plate rides up and over the other plate, this causes deep-sea trenches, and steep sided composite cone volcanoes. This only occurs where continental crust collides with oceanic crust or where oceanic crust collides with continental crust. • Continental crust can collide with continental crust and form folded mountains. • Examples: Mt. Everest, Mt. St. Helens, Mt. Fuji, Mt. Vesuvius

9. Continental VS Continental

10. Continental VS Oceanic

11. Oceanic Vs. Oceanic

12. Transform Boundaries Transform Boundary: plates slide past one another in opposite, but parallel directions. • Examples: San Andreas Fault

13. Transform

14. California Geology

15. External Earth Processes • Weathering: Breaking down rock into smaller pieces • Mechanical weathering: roots, animals, freeze-thaw: • Chemical: lichens, organic acids, acid rain and: • Erosion: Picking up small rocks and carrying them away • Wind: desert pavement, san dunes, abrasion • Water: beaches, levees, oxbow lakes, meanders • Ice: glaciers – Kettle lakes, moraine, till, u-shaped valleys, horns • Gravity: Mudslides, landslides

16. Erosion by Wind

17. Erosion by Water

18. Erosion by Glaciers

19. Erosion by Gravity

20. Mineral Resources and The Rock Cycle Mineral: naturally occurring, solid, inorganic Material with a crystalline structure and a Definite chemical composition Rock: Mixture of minerals Mineral Resource: a minerals that can extracted and converted into a resource at affordable prices

21. Natural Hazards • Earthquakes • Volcanoes • Floods • Mass Movements

22. Earthquake: stress in earth’s crust can cause solid rock to deform until it suddenly fractures and shifts along the fault producing a fault. • Two types of Earthquakes: • Deep-focus: caused when one plate slides under another plate (subduction), the plate gets jammed and pressure builds up, then with a sudden movement the plate slips under the other causing a very big earthquake. • Shallow focus: caused by plates sliding past one another. When the plates get locked up and then suddenly move the earthquake is created. • Epicenter: point on earth’s surface directly above the: • Focus: point where initial movement takes place. • Magnitude: size of quake measured on a logarithmic scale called the Richter scale. • Tsunami: earthquake generated water wave. • Control of quakes: geologic mapping, examine history records, building codes, ideally learn to predict

23. Volcanoes: when magma reaches earth’s surface through cracks or fissures 3 Types: • Composite Cone: large, steep sided, explosive, thick granitic magma, associated with convergent plate boundaries, lots of gas and ash. • Examples:

24. Shield Volcano Shield: flat, non-explosive, lots of liquid basaltic lava, associated with divergent plate boundaries and hot spots Example:

25. Mass Wasting: movement of rock by gravity • slump, creep, rockfalls, landslides, mudflows • factors that affect mass wasting: steepness of slope, amount of moisture, roads, building, fire • subsidence: land sinks and forms sinkholes. Caused when underground caves collapse. Can also be from removal of excess oil or groundwater • Example:

26. Soil composition Soil Horizons: series of layers or zones with a distinct texture and composition Soil profile: a cross-sectional view of horizons in soil O-horizon: top layer, surface litter which is leaves and debris A-horizon: topsoil layer: some inorganic materials and humus which is partially decomposed organic material. • these two top layers have fungi, bacteria, and protists that break down complex organic solids • A thick topsoil layer is good for crop. B-horizon: (subsoil) broken down inorganic rock C-horizon: parent rock

27. Leaching: • water infiltration occurs when precipitation occurs, this rain washes minerals out of the top layers of soil

28. Soil Texture: The relative amounts of clay, silt an sand, soil with equal amounts of each are called loams which are the best types for growing crops

29. Soil Porosity: a measure of the volume of pore spaces in the soil Soil Permeability: the rate that water moves through the soil, which is determined by soil porosity Soil porosity, texture and permeability determine a soils water holding capacity, aeration and workability

30. Soil Acidity: (pH), influences the uptake of soil nutrients by plants, also acid soil causes the leaching out of nutrients. PH of 5.5 to 8.5 is an acceptable range for most plants

31. Soil Erosion • Soil erosion is the movement of soil components from one place to another, usually from wind or water. Plant anchor the soil so that it is not washed away faster than it forms • Farming, logging, construction, overgrazing, off road vehicles, burning of vegetation all increase soil erosion • Losing topsoil makes soil less fertile and decreases its water holding capacity. The sediments also chokes lakes and streams

32. How serious is global erosion: • Topsoil is eroding faster than it forms on about on third of the earths cropland • Each year we must feed 90 million more people with 26 million tons less topsoil • The cost of erosion is about $400 billion worldwide in direct damage to agricultural lands, waterways, infrastructure and human health • In the U.S. soil is eroding 16 times faster than it can be replaced.

33. Desertification: process whereby the productive potential of arid or semi-arid land drops by 10% or more • Overgrazing, deforestation, surface mining, irrigation techniques that lead to increased erosion, salt buildup and water logging of soils, farming on land with unsuitable terrain or soil, soil compaction due to farm machinery and cattle hooves. • Every year an area the size of Kansas undergoes severe enough erosion to make farming not feasible in the area. • The only way to stop this is to reduce all the causes and to reforest land.

34. Irrigation • Most irrigation water has very dilute salts that build up over time in the soil, this is called salinization. • It takes thousands of years for precipitation to wash the salt out of the soil • Water logging occurs when too much water is applied to crops and this water sinks down into the groundwater causing the water table to rise and then salty water can envelope the roots of plants, killing them.

36. Soil Conservation • 1. Soil conservation: reducing the soil erosion and preventing and restoring soil fertility • Conventional tillage farming: the land is plowed and the soil is broken up and smoothed to make a planting surface

37. Conservation tillage: the idea is to disturb the soil as little as possible while planting crops. Special tillers break up and loosen only subsurface soil without overturning topsoil, previous crop residues, or any cover vegetation. This saves fuel, cuts costs, hold in more water, keeps soil from getting packed down and allows more of a crop growing season Terracing: reduces erosion on slopes by creating a series of broad level terraces. Contour farming: on gently sloping land, you plant rows across rather than down the sloped contour of the land.

38. Strip cropping: rows crops like corn are planted in strips with another crop like grasses or legumes that completely cover the soil Agroforestry: intercropping with trees Windbreaks and shelter breaks Land classification: classifying land that is not suited to agriculture PAM (polyacrylamide): Gel that hold soil together

39. Conserving soil fertility • 1.organic fertilizers • Animal manure: the best for crops but expensive to haul • Green manure: plowing under green vegetables • Compost • Crop rotation • 2. Inorganic fertilizers • Phosphorus, potassium and nitrogen • Easily transported, stored and applied, without them we would starve • Problems: wash into lakes and streams, they do not add humus to the soil, only supplies 2 or 3 out of some 20 needed materials

40. Nitrogen fixing by lightning Crop plant Organic fertilizers, Animal manure, Green manure, compost Commercial inorganic fertilizer 10-6-4 N-P-K Dead organic matter Nitrogen fixing Nutrient removal with harvest Application to land Decomposition Absorption of nutrients by roots Supply of available plant nutrients in soil Nutrient loss by bacterial processes such as conversion of nitrates to nitrogen gas Weathering of rock Fig. 10.14, p. 222 Nitrogen fixing by bacteria Nutrient loss from soil erosion