It also contains variable amounts of water vapor (H₂O), which is critical for weather and climate.
Physical Properties (Structure)
The atmosphere is layered vertically based on temperature changes:
Troposphere (0-12 km): The lowest layer, where we live. Temperature *decreases* with altitude. This is where all weather occurs.
Stratosphere (12-50 km): Temperature *increases* with altitude. This is because the ozone layer is here, which absorbs harmful UV radiation from the sun.
Mesosphere (50-80 km): Temperature *decreases* with altitude. This is where most meteors burn up.
Thermosphere (80+ km): Temperature *increases* dramatically due. Host to auroras and space stations.
Optical Properties
These properties describe how sunlight interacts with the atmosphere:
Scattering (Rayleigh Scattering): Gas molecules scatter short-wavelength light (blue and violet) more effectively than long-wavelength light (red). This is why the sky is blue and sunsets are red.
Reflection: The "bouncing" of light off a surface. A surface's reflectivity is its albedo. Clouds and ice have high albedo (reflect a lot of light), while oceans and forests have low albedo (absorb light).
Refraction: The bending of light as it passes through different densities of air. This is what creates rainbows and mirages.
2. Atmosphere: Circulation
Atmospheric circulation is the large-scale movement of air, driven by the fact that the equator receives more solar energy than the poles. This differential heating creates a global "heat engine" that tries to redistribute this energy.
If the Earth didn't rotate, hot air would simply rise at the equator and sink at the poles. But because the Earth *does* rotate, the flow is broken into three main "cells" in each hemisphere:
Hadley Cell (0° to 30°): Hot, moist air rises at the equator (low pressure, high rainfall - tropics). It flows poleward, cools, and sinks at 30° latitude (high pressure, dry - deserts).
Ferrel Cell (30° to 60°): The "middle" cell. It is driven by the other two and is responsible for the westerlies.
Polar Cell (60° to 90°): Cold, dense air sinks at the poles (high pressure) and flows equatorward.
This circulation, combined with the Earth's rotation (Coriolis effect), creates the major global wind patterns (e.g., Trade Winds, Westerlies).
Diagram: A cross-section of the Earth from equator to pole, showing the three circulation cells (Hadley, Ferrel, Polar) and the resulting high/low pressure zones and wind patterns.
3. Interfaces: Zones of Exchange
Interfaces are the boundaries where different Earth systems meet and interact, exchanging energy and matter.
Atmosphere-Ocean Interface:
Energy Exchange: The sun heats the ocean, and the ocean stores vast amounts of heat, which it releases slowly, moderating global climate.
Matter Exchange: Water evaporates from the ocean to the atmosphere. Gases like CO₂ dissolve from the atmosphere into the ocean (ocean acidification). Wind creates waves and drives surface currents.
Atmosphere-Land Interface:
Energy Exchange: Land heats up and cools down *quickly* (low specific heat) compared to water, creating daily temperature swings. Albedo (reflectivity) is a key factor.
Matter Exchange: Water evaporates from soil and transpires from plants (evapotranspiration). Wind erodes soil. Rain provides water for life and weathering.
Land-Ocean Interface (The Coastal Zone):
This is an extremely dynamic interface.
Processes: Tides (gravity), waves (wind), and river discharge (fluvial processes) all meet here.
Features: Results in features like beaches, deltas, estuaries, and cliffs.
4. Landforms: Constructional vs. Geomorphologic Processes
Landforms (like mountains, valleys, or deltas) are the result of a battle between two sets of processes:
Constructional (or Tectonic) Processes
These processes build up the land and create the "initial relief" or "first-order" landforms. They are driven by Earth's internal energy.
Tectonic Uplift: Plate collisions (convergent boundaries) that fold and fault rock to create mountain ranges (e.g., Himalayas).
Volcanism: Eruptions of magma/lava that build volcanoes and lava plateaus (e.g., Deccan Traps).
These processes wear down, reshape, and modify the initial landforms. They are driven by external energy (the sun) and gravity. This is the focus of Geomorphology.
Erosional Processes: *Wear down* and *carve* the land.
Example: A river cutting a V-shaped valley or a canyon. A glacier carving a U-shaped valley.
Depositional Processes: *Build up* land by *depositing* sediment.
Example: A river depositing silt to build a delta. Wind depositing sand to build a sand dune.
5. Types and Stability of Landforms
Types of Landforms (by agent)
Fluvial: Shaped by running water (e.g., V-shaped valleys, floodplains, deltas, canyons).
Glacial: Shaped by moving ice (e.g., U-shaped valleys, moraines, fjords).
Aeolian: Shaped by wind (e.g., sand dunes, yardangs).
Coastal: Shaped by waves and tides (e.g., beaches, sea cliffs, spits).
Karst: Shaped by the dissolution of soluble rock (limestone) (e.g., caves, sinkholes).
Stability of Landforms
Landform stability refers to a landform's resistance to change. Most landforms are not static; they exist in a state of dynamic equilibrium.
Dynamic Equilibrium: A state of balance where the rate of uplift or sediment input is balanced by the rate of erosion or sediment output. The landform may look the same over short timescales, but it is constantly being formed and destroyed at an equal rate.
A landform's stability is determined by:
Climate: A wet climate increases erosion (fluvial) and chemical weathering. A dry climate increases erosion (aeolian).
Geology (Rock Type): Hard, resistant rock (like granite) forms stable, steep landforms. Soft, weak rock (like shale) forms unstable, gentle slopes.
Tectonic Activity: Tectonically active areas (high uplift) have unstable, steep landforms and frequent disturbances (e.g., landslides).
Vegetation: Plant roots bind soil and rock, increasing stability and reducing erosion.
6. Ecosystem Dynamics (Geological Perspective)
This concept bridges geology and ecology. Geology and landforms provide the fundamental "stage" and "scenery" on which ecological processes (like ecosystem dynamics) play out. Geology controls ecology in several key ways:
Parent Material (Edaphic Factors): The type of underlying rock (parent material) weathers to form the soil. A limestone-derived soil will be alkaline (basic), while a granite-derived soil will be acidic. This soil chemistry is the primary control on what kind of plants (producers) can live there.
Topography (Slope and Aspect): Landforms create microclimates.
Slope: Steep slopes have thin, unstable soils and high water runoff. Flat floodplains have deep, rich soils.
Aspect: In the Northern Hemisphere, a south-facing slope gets more sunlight and is warmer and drier. A north-facing slope is cooler and wetter. This creates two completely different ecosystems on the same mountain.
Hydrology: Landforms control the flow of water. They determine where rivers, lakes, and wetlands will form, creating habitats.
Geological Disturbances: Processes like volcanoes, floods, and landslides act as major ecosystem disturbances. They wipe out existing communities, allowing for primary succession (on new lava) or secondary succession (on a floodplain after a flood).
In short: Geology → Landforms → Soil/Microclimate → Plant Community (Producers) → Animal Community (Consumers) → Ecosystem.