The Invisible Blanket: Earth's Atmosphere

Step outside — or just imagine it. You feel air on your skin, you breathe it in, and it blocks harmful radiation you can't even see. Yet you cannot hold it, weigh it easily, or see most of it. The atmosphere is one of Earth's most important systems, and it stretches hundreds of kilometres above you. Here's a thought: astronauts on the International Space Station (at about 400 km altitude) are technically still inside Earth's atmosphere, just in its outermost, almost-empty layers. That should hint at just how vast — and layered — our atmosphere really is.

Earth's atmosphere is a mixture of gases held in place by gravity. It has no sharp outer edge — it simply gets thinner and thinner until it fades into space. Scientists divide it into four main layers based on how temperature changes with altitude. **Composition of the atmosphere** Dry air at ground level is made up of roughly 78 % nitrogen (N₂), 21 % oxygen (O₂), 0.9 % argon, and about 0.04 % carbon dioxide (CO₂), plus tiny amounts of other gases and variable amounts of water vapour. Nitrogen is largely inert — it dilutes oxygen so that fires and reactions do not burn out of control. Oxygen is essential for the respiration of most living things. Carbon dioxide, though a tiny fraction, plays a crucial role in regulating temperature. **The four layers** 1. **Troposphere (0–12 km):** This is where you live and where all weather happens. Temperature drops with altitude at about 6.5 °C per kilometre. It contains roughly 80 % of the atmosphere's total mass. Commercial aircraft fly near the top of this layer. 2. **Stratosphere (12–50 km):** Temperature rises here because the ozone layer absorbs ultraviolet (UV) radiation from the Sun. The ozone layer — a region rich in ozone molecules (O₃) — acts as a shield, blocking most UV-B and UV-C rays that would damage DNA in living cells. 3. **Mesosphere (50–85 km):** Temperature drops again, making this the coldest layer (as low as −90 °C). Most meteors burn up here due to friction with air particles, which is why we see 'shooting stars'. 4. **Thermosphere (85–600+ km):** Temperature rises sharply — reaching over 2 000 °C — because high-energy solar radiation is absorbed directly. However, the air is so thin that very little heat is felt. The Northern and Southern Lights (auroras) occur here. **The greenhouse effect** Some gases — especially CO₂, methane (CH₄), and water vapour — absorb heat (infrared radiation) radiating from Earth's surface and re-emit it back downward. This is the **greenhouse effect**. Without it, Earth's average temperature would be about −18 °C instead of the current +15 °C. However, human activities (burning fossil fuels, deforestation, farming) are increasing CO₂ and methane levels, enhancing the greenhouse effect and causing global average temperatures to rise — a process called **climate change**.