Rucete ✏ Biology In a Nutshell
1. Formation of Earth and Its Atmosphere
- The Earth formed approximately 4.6 billion years ago.
- Early atmosphere likely consisted of hydrogen (H₂), methane (CH₄), ammonia (NH₃), and water vapor (H₂O)—but lacked oxygen (O₂).
2. Formation of the Primordial Seas
- Earth cooled, and water vapor condensed, forming the first oceans or primordial seas.
- These provided a medium for chemical reactions.
3. Synthesis of Organic Molecules
- Energy from lightning, UV radiation, and volcanoes allowed inorganic molecules to form organic molecules, such as amino acids and nucleotides.
- Supported by the Miller-Urey experiment.
4. Formation of Polymers and Self-Replicating Molecules
- Organic monomers linked to form polymers (e.g., proteins, RNA).
- Some RNA molecules could self-replicate—this led to the RNA world hypothesis.
5. Formation of Protobionts
- Organic molecules clustered into membrane-like structures called protobionts.
- These structures maintained an internal environment, a step toward life.
6. Heterotrophic Prokaryotes
- First life forms were likely anaerobic heterotrophic prokaryotes, feeding on organic molecules in the seas.
7. Autotrophic Prokaryotes
- Some prokaryotes evolved the ability to perform photosynthesis, releasing oxygen as a byproduct.
8. Oxygen Accumulation and Ozone Layer Formation
- Oxygen accumulated in the atmosphere → formed the ozone layer (O₃).
- Ended abiotic chemical evolution by shielding Earth from UV radiation.
9. Origin of Eukaryotes (Endosymbiotic Theory)
- Eukaryotic cells formed via endosymbiosis—larger cells engulfed smaller ones (e.g., mitochondria and chloroplasts) that became organelles.
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Biology in a nutshell