# Explain how the chemical conditions on early Earth could have supported the abiotic synthesis of organic monomers necessary for the origin of life.

> IB DP Biology Standard Level (2023 syllabus) — A2.1 Origins of cells · Explain · 4 marks

> Scientists hypothesise that life on Earth originated approximately 3.5–4 billion years ago, when the planet's surface and atmosphere differed dramatically from today.

## Mark scheme (4 marks)

1. The early atmosphere lacked free oxygen / was a reducing atmosphere, preventing oxidation of organic molecules.
2. Simple inorganic molecules / gases (such as methane, ammonia, hydrogen, water vapour) were present and could serve as raw materials for organic synthesis.
3. Energy sources such as lightning, UV radiation, or heat from hydrothermal vents could drive chemical reactions between these simple molecules.
4. These reactions could produce organic monomers such as amino acids / simple sugars / nucleotides / nucleobases abiotically, as demonstrated experimentally (e.g. Miller–Urey experiment).

## Key terms

- [abiotic synthesis](https://www.gradenine.co.uk/glossary/abiotic-synthesis)
- [organic monomers](https://www.gradenine.co.uk/glossary/organic-monomers)

## Related

- [Revision notes for IB DP Biology Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-chemical-conditions-on-1ea692a7) · Published by Druglandscape Ltd.