Before you can understand how the atmosphere has changed, you need to know what it's made of today. This video gives you the three main gases and their percentages in a form you can use in any question — as fractions, percentages, ratios, or parts per million — and explains why that composition has barely changed in 200 million years. Short, focused, and exactly what the GCSE specification asks you to recall.

What You Will Learn

00:12How thick the Earth's atmosphere is and why only the first few kilometres sustain human life.

02:20What the three main gases in today's atmosphere are and their approximate percentages.

02:33Why nitrogen at 78% is the most abundant atmospheric gas, not oxygen.

02:51What argon's role is and its approximate 1% share.

02:58Why carbon dioxide at only 0.04% is significant despite its small proportion.

03:19What parts per million (ppm) means as a unit and how to relate it to percentages.

05:17How long the current atmospheric proportions have been approximately stable.

05:31How to express atmospheric composition as fractions, percentages, ratios, and ppm.

Take a journey back 4.6 billion years and watch Earth's atmosphere transform from a volcanic mix of methane, ammonia, and water vapour into the nitrogen-oxygen balance we breathe today. This video walks you through each stage — from the cooling oceans locking away carbon dioxide to photosynthesis flooding the air with oxygen — and connects each change to the chemistry behind it. Essential viewing before tackling air pollution or the carbon cycle.

What You Will Learn

00:58How to describe the composition of the present-day atmosphere and identify which gases make up the remaining 1%.

02:58Why scientists cannot be certain about the exact sequence of events in the atmosphere's development 4.5 billion years ago.

04:22Why evidence from Mars and Venus supports the idea that Earth's early atmosphere was high in carbon dioxide.

06:08How volcanic activity released gases to form Earth's early atmosphere, which was mostly carbon dioxide and water vapour.

07:58How the formation of oceans caused CO₂ levels to fall by dissolving into seawater and forming carbonate rocks.

09:11What the word and symbol equations for photosynthesis are and how photosynthetic bacteria transformed the atmosphere.

10:44How to write a structured six-mark exam answer explaining the development of Earth's atmosphere.