6.1.1 The atmosphere forms the boundary between Earth and space. It is the outer limit of the biosphere and its composition and processes support life on Earth.

6.1.2 Differential heating of the atmosphere creates the tricellular model of atmospheric circulation that redistributes the heat from the equator to the poles.

6.1.3 Greenhouse Gases (GHGs) and aerosols in the atmosphere absorb and re-emit some of the infrared (long-wave) radiation emitted from the Earth’s surface, preventing it from being radiated out into space. 

They include the greenhouse gases water vapour, carbon dioxide, methane and nitrous oxide (N2O), and black carbon (aerosol).

6.1.4 The greenhouse effect keeps the Earth warmer than it otherwise would be due to the broad spectrum of the Sun’s radiation reaching the Earth’s surface and infrared radiation emitted by the warmed surface then being trapped and re-radiated by GHGs.

6.1.5 The atmosphere is a dynamic system, and the components and layers are the result of continuous physical and chemical processes.

6.1.6 Molecules in the atmosphere are pulled towards the Earth’s surface by gravity. Because gravitational force is inversely proportional to distance, the atmosphere thins as altitude increases.

6.1.8 Global warming is moving the Earth away from the glacial–interglacial cycle that has characterized the Quaternary period, toward new, hotter climatic conditions.

6.1.7 Milankovitch cycles affect how much solar radiation reaches the Earth and lead to cycles in the Earth’s climate over tens to hundreds of thousands of years.

6.1.9 The evolution of life on Earth changed the composition of the atmosphere, which in turn influences the evolution of life on Earth.