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Earth's Shape and Coordinate System

Shape

Earth is an oblate spheroid, meaning it bulges at the equator and is flattened at the poles. This shape is due to the centrifugal force created by Earth's rotation. Earth is also slightly pear-shaped due to the uneven distribution of continents and the gravitational pull of the moon.

Coordinate System:

Latitude

• Measures angular distance north or south of the equator.

• Ranges from 0° at the equator to 90° at the poles.

• Lines of equal latitude are called parallels.

• Examples: 41°N (Storrs, CT), 34°S (Sydney, Australia)

Longitude

• Measures angular distance east or west of the prime meridian.

• Ranges from 0° at the prime meridian to 180° at the international date line.

• Lines of equal longitude are called meridians.

• Examples: 72°W (Storrs, CT), 151°E (Sydney, Australia)

Longitude and Time Zones

• Time Zones: Earth is divided into 24 time zones, each spanning 15° of longitude.As you move eastward, you gain an hour for each time zone crossed.

  • Example: If it's 12:00 PM in Storrs, CT, it's 5:00 PM in Greenwich, England.

• International Date Line: Located at approximately 180° longitude.Crossing the line moving eastward, the date goes back one day.Crossing westward, the date advances one day.

Equinoxes and Solstices

• Equinoxes: Occur twice a year, around March 21st (vernal equinox) and September 23rd (autumnal equinox).The sun is directly overhead at the equator.Day and night are approximately equal in length worldwide.

• Solstices: Occur twice a year, around June 21st (summer solstice) and December 21st (winter solstice).The sun is directly overhead at the Tropic of Cancer (23.5°N) during the summer solstice and the Tropic of Capricorn (23.5°S) during the winter solstice.The longest day of the year in the Northern Hemisphere is during the summer solstice, and the shortest day is during the winter solstice.

Hydrologic Cycle

• Process: Continuous movement of water in its various states (solid, liquid, gas) through Earth's systems.

• Components:

  • Evaporation: Liquid water changes to water vapor.

  • Transpiration: Water loss from plants.

  • Condensation: Water vapor changes to liquid water, forming clouds.

  • Precipitation: Water falls back to Earth as rain, snow, sleet, or hail.

  • Infiltration: Water seeps into the ground.

  • Runoff: Water flows over land into rivers, lakes, and oceans.

Earth's Formation and Layers

• Formation: Earth formed from the accretion of dust and gas in a protoplanetary disk around the sun.

• Layers:

  • Inner Core: Solid, composed primarily of iron and nickel.

  • Outer Core: Liquid, also composed of iron and nickel.

  • Mantle: Thickest layer, composed of mostly solid rock.

  • Crust: Outermost layer, two types:

    • Oceanic: Denser, composed of basalt.

    • Continental: Less dense, composed of granite-type rock.

Isostasy

• Concept: The state of gravitational equilibrium between Earth's crust and mantle such that the crust "floats" at an elevation that depends on its thickness and density.

• Example: Continental crust is thicker and less dense than oceanic crust, so it "floats" higher on the mantle.

Theory of Plate Tectonics

• History: Developed from the continental drift hypothesis and seafloor spreading hypothesis.

• Evidence:

  • Continental Drift: Fit of continents, fossil distribution, matching rock units, etc.

  • Seafloor Spreading: Magnetic anomalies, heat flow, sediment age, etc.

• Plate Boundaries:

  • Divergent: Plates move apart, creating new crust (mid-ocean ridges).

  • Convergent: Plates collide, destroying crust (trenches, mountains).

  • Transform: Plates slide past each other (fracture zones).

Sediments

• Classification:

  • Location: Neritic (near shore) and pelagic (deep ocean).

  • Particle Size: Gravel, sand, silt, clay.

• Source and Chemistry:

  • Lithogenous: From land (rocks, etc.).

  • Biogenous: From organisms (shells, etc.).

  • Hydrogenous: From chemical reactions in water.

  • Cosmogenous: From space (meteorites).

Physical and Chemical Properties of Water

• Physical Properties:

  • Cohesion: Water molecules stick together.

  • Adhesion: Water molecules stick to other substances.

  • High Specific Heat: Water can absorb a lot of heat without a large temperature change.

  • Expansion on Freezing: Ice is less dense than liquid water.

  • Solvent: Dissolves many substances.

• Chemical Properties:

  • Salinity: Total salt content, average 35‰ (parts per thousand).

  • Major Constituents: Six ions (Cl-, Na+, SO42-, Mg2+, Ca2+, K+) make up >99% of dissolved salts.

  • Principle of Constant Proportions: Ratios of major ions remain constant.

  • Gases: N2 > O2 > CO2

  • Solubility: Affected by temperature, salinity, and pressure.

  • pH: Measure of acidity/alkalinity.

  • Buffers: Substances that resist changes in pH, like the carbonate system in seawater.