This definitions covers Key Definitions within Composition of Atmosphere for GCSE Chemistry. Revise Composition of Atmosphere in Atmosphere for GCSE Chemistry with 20 exam-style questions and 12 flashcards. This topic appears less often, but it can still be a useful differentiator on mixed-topic papers. It is section 6 of 13 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Topic position
Section 6 of 13
Practice
20 questions
Recall
12 flashcards
📖 Key Definitions
Atmosphere: The layer of gases surrounding Earth, held in place by gravity. Approximately 78% nitrogen, 21% oxygen, 0.9% argon, 0.04% carbon dioxide.
Photosynthesis: The process by which green plants and algae use light energy to convert carbon dioxide and water into glucose and oxygen. 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Cyanobacteria: Ancient photosynthetic bacteria (blue-green algae) — the first organisms to produce oxygen through photosynthesis, responsible for the Great Oxidation Event.
Fossil fuels: Coal, oil, and natural gas formed from the remains of ancient organisms buried and compressed over millions of years. They contain carbon locked away from the ancient atmosphere.
Outgassing: The release of gases from rocks through volcanic activity, which formed Earth's early atmosphere.