Evolution — Syllabus
Tamil Nadu Board · Class 12 · Zoology
What Evolution covers in Tamil Nadu Board Class 12 Zoology: 4 topics, for the 2026-27 session. Part of the Tamil Nadu Board Class 12 Zoology syllabus.
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Topics in Evolution
6.1 Origin of Life and Evolution of Life Forms
- Earth's age: approximately 4.5-4.6 billion years (determined by radiometric dating of meteorites)
- Theory of Special Creation: Life was created by a supernatural power (God) according to religious beliefs
- Abiogenesis/Spontaneous Generation: Living organisms originated from non-living materials through chemical and molecular evolution over millions of years. Coined by Thomas Huxley
6.2 Geological Time Scale
- Earth's history divided into major Eras: Paleozoic, Mesozoic, and Cenozoic
- Paleozoic Era (510-230 million years ago): Age of Invertebrates and emergence of vertebrates except birds and mammals
- Six periods of Paleozoic: Cambrian (invertebrates), Ordovician (fresh water fishes, molluscs), Silurian (origin of fishes), Devonian (Age of Fishes), Mississippian (earliest amphibians), Pennsylvanian
6.3 Biological Evolution - Formation of Protobionts
- Protobionts: Abiotically produced molecules self-assemble into droplets enclosing watery solutions
- Liposomes: Lipids in solution that self-assemble into lipid bilayers; first membrane-like structures
- Proteins inside liposomes acquired enzyme properties, enabling faster molecular reproduction
6.4 Evidences for Biological Evolution
- Paleontological Evidence: Fossils are true witnesses of evolution; found in sedimentary rock strata
- Three categories of fossilization: Actual remains (original hard parts preserved), Petrifaction (molecule-by-molecule replacement by minerals), Natural moulds and casts (impressions in hardened rock)
- Actual remains examples: Woolly Mammoth preserved in frozen Siberia (22,000 years old), residents of Pompeii preserved in volcanic ash
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