Structure, Layers, and the Greenhouse Effect Earth’s Atmosphere Structure, Layers, and the Greenhouse Effect

Elevation Density and Pressure The Atmosphere extends to hundreds of km above the Earth The Weight of the upper layers pushes down generating pressure concentrating the air in the lowest layer. Thus Elevation is inversely related to both pressure and density.

The Troposphere or “Weather Sphere” From 0 – 18 km, the lowest layer Most dense, containing 70 – 80 % of the air Most weather and clouds occur here Elevation and Temperature are inversely related

The Stratosphere or “Blanket-sphere” 18 – 50 km elevation Little weather occurs here, flat stratus clouds in the lower levels & High winds (Jet streams) Elevation and temperature are directly related Near the top is a thin layer of Ozone (O3) that blocks UV light.

Mesosphere “Middle-sphere” 50 – 90 km Very low density Elevation and temperature are inversely related

Ionosphere 90 – 400 km So little density its almost “space” Made of Ionized Gas Temperature and Elevation are directly related Aurora Borealis occurs here

The Greenhouse Effect The Atmosphere lets visible light pass through but absorbs most infrared light Light reaches Earth’s surface which is warmed and radiates Infrared light which is absorbed Thus trapped by the atmosphere, and… The average temperature rises. Temperatures are more moderate Some gasses called “green house gasses” (such as CO2) absorb better than others. If they increase so will the average temperature