The Four Greek Elements

The ancient Greeks recognized four elements - fire, earth, water, and air. While modern chemistry tells us that these are not true elements, they are elemental components of the world around us. We can understand much about our world by examining the cycles of form and function that these four follow. Earth Science begins with the fiery furnace that created our solar system many billions of years ago. After a brief tour of the planetary neighborhood, we get down to earth.

Here we begin to see how nature's cycles impact every aspect of living on Earth. Tides, like fools, rush in, driven by cycles of the Moon. We have day and night because the Earth rotates; we have seasons because our tilted Earth revolves around the Sun. And, uniquely on Earth, the Blue Planet, we find water.

Water — cycling through the world ocean and freshwater systems, over land, and back again — is a powerful force of nature. It carves river valleys, drives ocean currents, and helps to determine global climates. And it's even water in the very air we breathe that distributes heat energy around the world, driving our weather patterns.

Wetlands are fragile ecosystems

Fire, earth, water, and air - powerful forces that shape our world, yet how fragile they seem in the face of human indifference. We cut down a few trees, burn some fossil fuels, pave some roads, and suddenly, a delicate balance is disturbed. What we put into the air may fall to Earth as acid rain. The trees we harvest can no longer prevent soil erosion. The pavement we spread increases runoff and flooding. The more we can understand the interconnectedness of Earth's systems, the better we can play our part as stewards, protecting and preserving for tomorrow the majesty we enjoy today.

It's a small world, after all.

1. Earth Within the Solar System
   1. Evolution of the Solar-Centric Model
   2. Earth's Location and its Effects
   3. Here Comes the Sun
   4. The Magnetosphere
   5. Fly Me to the Moon
2. Earth's Cycles: Rotation and Revolution
   1. The Spin We're In
   2. Night and Day
   3. Tidal Force
   4. The Reasons for Seasons
3. The Water Cycle
   1. Evaporation
   2. Condensation
   3. Transport
   4. Precipitation
   5. Groundwater
   6. Transpiration
   7. Runoff
4. Oceanography
   1. Oceanic Layers and Composition
   2. Surf's Up! All About Waves
   3. Current Events
   4. Continental Margins
   5. Ocean Basins
   6. Oceanic Ice
   7. Ocean Resources
5. Surface Water Systems
   1. Lakes, Swamps, and Marshes
   2. Rivers and Streams
   3. Groundwater
   4. The Water Table
   5. Surface Water Systems and Society
6. Atmospheric Structure and Composition
   1. There's Something in the Air
   2. Troposphere: All Mixed Up
   3. Stratosphere: The Ozone Zone
   4. Mesosphere: The Big Chill
   5. Thermosphere: Lonely at the Top
7. Earth's Climate
   1. Climate Zones
   2. Temperature Factors
   3. Precipitation Factors
   4. Climatic Change
8. How's the Weather?
   1. Under Pressure
   2. Temperature
   3. Wind
   4. Moisture
   5. Clouds
9. Taking Turns: Weather Patterns
   1. Turn and Churn: The Coriolis Effect
   2. Solar Effects
   3. Jet Stream
   4. El Niņo
10. Wild and Woolly Weather
    1. Thunderstorms
    2. Tornadoes
    3. Hurricanes
    4. Cyclonic Storms