Early Earth's atmosphere was reducing, so what did Miller actually put in the flask? Chemical evolution vs Pasteur confuses me
Riya Singh12th Sample
13 Aug 2026 · 1 min read
The Evolution chapter starts with such big words (Big Bang, chemical evolution, panspermia) and I find my mind wandering. Let me try to write what I think I got and someone please bust the myths.
Big Bang: universe began as a single huge explosion and has been expanding since; hydrogen and helium, then galaxies, then our solar system. Earth was about 4.5 billion years old and had no oxygen in the beginning. The atmosphere had water vapour, methane, CO2 and ammonia (from molten mass). UV rays broke water into hydrogen and oxygen, hydrogen escaped, and oxygen combined with NH3 and CH4 to form water, CO2 and others, then an ozone layer formed.
Questions:
- Was Miller's atmosphere the same as the above? What did he use in the apparatus and what formed?
- Oparin and Haldane say life came from pre-existing non-living organic molecules. But Pasteur said life only comes from life. Isn't that a contradiction? NCERT mentions both.
- What is "panspermia" and is it accepted?
7 answers & replies
Sign in to join the conversation.
[+][–]Siddharth RaoDropperSample· 2mo ago
Your summary matches NCERT well. The key point is that the early atmosphere was reducing (rich in hydrogen-containing gases like CH4, NH3, water vapour, and no free O2). That's why organic molecules could form and survive for a long time. In today's oxygen-rich air, simple organic molecules would be oxidised before accumulating. Oxygen showed up much later when photosynthesis started.
[+][–]Nisha Verma12thSample· 2mo ago
Miller's experiment (1953): closed flask, circulating gases, electric discharge (like lightning) at 800 °C to mimic early Earth, using CH4, H2, NH3 and water vapour... and oxygen as well so that it matches air back then. Amino acids formed after a few days.
[+][–]Rahul DubeyDropperSample· 2mo ago
Nisha, there's no oxygen in Miller's mixture, that's the whole point. Mixture: CH4, H2, NH3 and water vapour, at 800 °C, with electric discharge. The reducing atmosphere. If oxygen was in, the experiment would have shown nothing useful for the origin-of-life idea. Product: amino acids. Other scientists doing similar experiments later got sugars, nitrogen bases, pigments and fats.
[+][–]Nisha Verma12thSample· 2mo ago
you're right rahul, I put O2 in by mistake. It's a reducing atmosphere. Thanks for the catch
[+][–]Tanvi Deshmukh12thSample· 2mo ago
About Pasteur: he showed with his experiments (the famous swan-neck flask where boiled broth stayed clear) that life comes from pre-existing life and disproved spontaneous generation (the older idea that life arises from decaying matter, like mud producing worms). That's about life today. Oparin and Haldane suggested that the first life on a primitive Earth arose slowly through chemical evolution: first simple organic molecules, then bigger molecules like RNA, proteins, polysaccharides, then cell-like forms. Today's conditions don't allow it, so no contradiction.
[+][–]Riya Singh12thSample· 2mo agoAuthor
this swan-neck explanation kills the contradiction in my head, thank you. "life now from life, first life from chemistry". Writing that in my diary lol
[+][–]Kavya NaikDropperSample· 2mo ago
Panspermia: idea that "spores" of life were already present everywhere in the universe, including on other planets, and came to Earth from outer space. NCERT says that many accept chemical evolution rather than panspermia as the explanation. Panspermia doesn't explain how it first started anywhere else either, it just shifts the question.
