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 regularly enough that it should still be part of a steady revision cycle. 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.
📖 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.
Practice questions for Composition of Atmosphere
What is the approximate percentage of nitrogen in the current atmosphere?
Describe how Earth's early atmosphere was formed.