Atmosphere – A Level Environmental Science AQA Revision

The Earth’s atmosphere consists of approximately 78% nitrogen, 21% oxygen, and 1% other gases including argon, carbon dioxide, neon, helium, and methane.
Water vapour varies in amount, ranging from almost zero in polar regions to about 4% in tropical regions.
The atmosphere is divided into several layers: the troposphere, stratosphere, mesosphere, thermosphere, and exosphere, each having unique characteristics.

The atmosphere protects life on Earth by absorbing extreme ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night.
The Ozone layer in the stratosphere absorbs most of the Sun’s harmful ultraviolet rays.
The atmosphere provides all the necessary gaseous elements essential for life: carbon, oxygen, and nitrogen.
Rain and other forms of precipitation deliver water essential for life from the atmosphere to Earth.

Human activities, such as burning fossil fuels, have increased the concentration of greenhouse gases (e.g. carbon dioxide, methane) in the atmosphere, contributing to global warming and climate change.
Climate change can result in habitat loss, species extinction, and changes in the distribution of organisms.
Increased carbon dioxide in the atmosphere leads to ocean acidification, impacting marine life.

Oxygen is essential for respiration, a process through which organisms generate energy.
Nitrogen is an important element of amino acids, proteins, and DNA, which are critical to life. Nitrogen in the atmosphere is converted into a usable form for plants by bacteria through the nitrogen cycle.
Carbon dioxide is key for photosynthesis, the process plants use to convert light energy into chemical energy.

The carbon cycle and nitrogen cycle are key feedback mechanisms in the atmosphere. These cycles involve the movement of elements between the atmosphere, biosphere, lithosphere, and hydrosphere and ensure the availability of these elements in a form usable for life.
Feedback mechanisms such as the water vapour feedback and the cloud feedback play significant roles in Earth’s climate system. Changes in these systems due to human activities can amplify or reduce warming trends.