No questions found in this category.
The Earth’s atmosphere is a vital, multi-layered envelope of gases held in place by gravity, essential for sustaining life on our planet. A key component of General Knowledge, its composition and structure are fundamental to understanding Earth’s systems. The dry air in the atmosphere is primarily composed of Nitrogen (approximately 78%) and Oxygen (about 21%). The remaining 1% consists of trace gases, with Argon being the most abundant at roughly 0.93%, followed by a tiny fraction of Carbon Dioxide (around 0.04%). The atmosphere also contains a variable amount of water vapor, which is crucial for weather phenomena and the water cycle.
This gaseous shield is divided into five distinct layers, each with unique characteristics determined mainly by temperature variations.
- Troposphere: This is the lowest and densest layer, extending from the surface up to an average of 12 kilometers. It is where we live, and it contains roughly 75-80% of the atmosphere’s total mass. The vast majority of weather events, including clouds, rain, and storms, occur here. As altitude increases in the troposphere, the temperature decreases.
- Stratosphere: Located above the troposphere, this layer extends to about 50 kilometers. It is best known for containing the ozone layer, a region with a high concentration of ozone gas () that absorbs and filters out most of the sun’s harmful ultraviolet (UV) radiation. Unlike the troposphere, the temperature in the stratosphere actually increases with altitude due to this absorption of UV energy. Its stable, calm nature makes it the preferred layer for jet aircraft to fly.
- Mesosphere: From 50 to 85 kilometers, the mesosphere is characterized by a significant drop in temperature, making its top boundary, the mesopause, the coldest place in the Earth’s atmosphere. This is the layer where most meteors burn up upon entering the atmosphere, creating the brilliant streaks of light we see as “shooting stars.”
- Thermosphere: Extending from about 85 kilometers to 600 kilometers, this layer is incredibly thin, yet its temperature soars to hundreds or even thousands of degrees Celsius due to the absorption of high-energy solar radiation. The air is so sparse that it would feel freezing to us, but the individual molecules are highly energetic. The aurora borealis (Northern Lights) and aurora australis (Southern Lights) are spectacular phenomena that occur in this layer, as are the orbits of low-Earth orbit satellites, including the International Space Station (ISS).
- Exosphere: The outermost layer of the atmosphere, the exosphere gradually thins out and merges with the vacuum of outer space. Primarily composed of hydrogen and helium atoms, these particles are so widely spaced that they rarely collide and can eventually escape Earth’s gravity. It represents the final transition from our planet to the cosmos.
Beyond providing the air we breathe, the atmosphere’s overall function is to create a habitable environment. It protects us from dangerous UV radiation, incinerates incoming space debris, and maintains the planet’s temperature through the greenhouse effect, preventing extreme temperature fluctuations between day and night.
