Evidence for the origin of carbon compounds: the Miller–Urey experiment
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Question
What does 'abiotic' synthesis mean?
Answer
Organic molecules forming **without any living organisms** — by chemistry from **inorganic** precursors plus energy.
Question
Define a monomer.
Answer
A small **building-block** molecule; many monomers join to make a **polymer** (e.g. amino acids → proteins).
Question
What gas mixture did Miller and Urey use?
Answer
A **reducing** mix of **methane (CH₄), ammonia (NH₃), hydrogen (H₂) and water vapour** — modelling the early atmosphere.
Question
What did the Miller-Urey experiment produce, and what did it show?
Answer
It produced **amino acids** and other organic monomers, showing that organic molecules can form **abiotically**, without life.
Question
Name two proposed sources of organic molecules OTHER than the early atmosphere.
Answer
**Deep-sea hydrothermal vents** (mineral-catalysed synthesis) and **extraterrestrial delivery** on meteorites (e.g. the **Murchison** meteorite).
Question
Why must monomers form before polymers?
Answer
Polymers are **chains of monomers**, so the building blocks must exist **first** — this is **step 1** of the origin of cells.
Question
Why did a reducing (oxygen-free) atmosphere matter for prebiotic synthesis?
Answer
Free **oxygen** would destroy organic molecules, so the lack of oxygen let the new monomers **survive and accumulate**.
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Origins of cells
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