The Dawn of Life: Early Earth Systems and Abiogenesis
Classified in Biology
Written on in 
English with a size of 2.43 KB
1. Evidence of Earth's Ancient Non-Living Systems and Evolution
- Geosphere:
- Oldest crust: Acasta Gneiss (4.04 Ga); Zircon crystals in Jack Hills Conglomerate (4.4 Ga).
- Plate tectonics likely began ~3.2 Ga, evidenced by diamond inclusions transitioning from peridotite to eclogite.
- Atmosphere:
- Initial gases (Hydrogen, Helium) lost to solar winds; later volcanic outgassing formed a CO₂ and water-rich atmosphere.
- Oxygen appeared ~2.3 Ga due to cyanobacteria, evidenced by oxidized minerals (Banded Iron Formations).
- Hydrosphere:
- Water sources: Asteroids (carbonaceous chondrites) and volcanic outgassing.
- Oceans formed as Earth cooled and water vapor condensed.
2. Definition of Life and Origin of Components
- Definition: Life is distinguished by:
- Barrier-separated systems (cell membrane).
- Growth, reproduction, metabolism, and evolution.
- Origin of Components:
- Extraterrestrial: Organic molecules (e.g., amino acids) found in meteorites (e.g., Murchison Meteorite).
- Atmosphere: Urey-Miller experiment synthesized amino acids in early Earth conditions.
- Hydrothermal Vents: Alkaline vents produce organic molecules via reactions with CO₂ and hydrogen.
3. Possible Locations for the Origin of Life
- Warm Little Pond: Rich organic molecules proposed by Darwin.
- Tide Pools and Hot Springs: Concentrated organics in cyclic environments.
- Hydrothermal Vents:
- Off-axis vents: Long-lived, alkaline systems with steady organic production.
- Black smokers: Less likely due to extreme heat and acidity.
4. Mechanisms of Cellular Evolution
- RNA World Hypothesis:
- RNA as the first replicating molecule with metabolic-like activity.
- RNA self-replication without protein enzymes.
- Membrane Formation:
- Fatty acids formed bilayers, encapsulating organic molecules into "protocells".
- Membranes allowed concentration of organics and energy gradients for metabolism.
- Energy Gradients: Proton gradients in alkaline vents mimicked by early cells to produce energy (similar to mitochondria).