Earth and the Geographic Grid

• Geography studies Earth's surface and atmosphere, including human-environment interactions.

Earth as a Planet

• Earth, the third planet from the Sun, is the largest terrestrial planet.
• Its shape is an oblate spheroid, being spherical but flattened at the poles and bulging at the Equator.
• Earth's layers consist of the crust, mantle, outer core, and inner core.
• Earth remains the only known planet to support life.

Geographic Grid

• The geographic grid is a coordinate system for locating any point on Earth.
• This system uses lines of latitude and longitude.
• Latitude lines run east to west, parallel to the Equator, measuring distances north or south of it.
• The Equator is 0° latitude, while the North and South Poles are 90° N and 90° S.
• Longitude lines run north to south, converging at the poles, measuring distances east or west of the Prime Meridian.
• The Prime Meridian is 0° longitude, passing through Greenwich, England.
• Latitude and longitude coordinates specify locations on Earth.

Rotation and Revolution

• Earth's rotation is its spin on its axis, an imaginary line through the North and South Poles.
• One rotation takes about 24 hours, defining a day.
• Rotation causes the cycle of day and night.
• Earth's revolution is its orbit around the Sun.
• One revolution takes about 365.25 days, defining a year.
• The 23.5° tilt of Earth's axis results in varying sunlight amounts, causing seasons.

Composition and Structure of Atmosphere

• The atmosphere is a layer of gases held by gravity.
• Major components include approximately 78% nitrogen, 21% oxygen, with smaller amounts of argon, carbon dioxide, and other trace gases.
• The atmosphere has layers, divided by temperature gradients.
• From the surface up, these layers are the troposphere, stratosphere, mesosphere, thermosphere, and exosphere.
• The troposphere, the lowest layer, is where weather occurs.
• The stratosphere contains the ozone layer, which absorbs ultraviolet radiation.
• The mesosphere is where meteors burn up.
• The thermosphere is the orbit location of the International Space Station; auroras also occur here.
• The exosphere is the outermost layer, fading into space.

Insolation

• Insolation is incoming solar radiation, the solar energy received per unit area on Earth's surface.
• Factors affecting insolation include:
  • Angle of incidence: Direct sunlight (90°) concentrates energy, increasing insolation, while oblique angles spread energy, reducing insolation.
  • Latitude: Regions near the Equator receive more direct sunlight, resulting in higher insolation, compared to higher latitudes.
  • Atmospheric conditions: Clouds, dust, and gases can absorb, reflect, or scatter solar radiation, decreasing insolation.
  • Day length: Longer days increase total insolation per day.
  • Earth's orbit: Earth's elliptical orbit causes slight variations in distance from the Sun, affecting solar radiation received.
• Insolation drives Earth's climate system, influencing temperature, weather, and ecosystem distribution.

Fundamentals of geography, including Earth's structure and the geographic grid system. Topics covered include Earth's shape, layers, and its unique ability to support life. Learn about latitude and longitude, and how they form a coordinate system to locate any point on Earth's surface.