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- February 8, 2025
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Key periods in the Geological Time Scale: Cambrian, Jurassic, Cretaceous, and Quaternary periods.
The Geological Time Scale divides Earth’s history into distinct intervals marked by significant biological, climatic, and tectonic events. For UPSC aspirants, understanding Cambrian, Jurassic, Cretaceous, and Quaternary periods is crucial for grasping evolutionary milestones, fossil records, and India’s geological heritage. These periods highlight Earth’s dynamic history and its relevance to contemporary environmental and geographical studies.
Table of Contents
Cambrian Period (541–485 Million Years Ago)
The Cambrian Period marks the Cambrian Explosion, a rapid diversification of marine life, including the first appearance of hard-shelled organisms like trilobites and brachiopods. This period laid the foundation for complex ecosystems, with the evolution of predators and prey driving biodiversity. The Burgess Shale in Canada and Chengjiang Biota in China preserve exceptional fossils from this era.
⦿ Evolutionary Significance: Development of exoskeletons and complex body plans.
⦿ Climate: Shallow seas and warm global temperatures dominated.
India’s Context: The Marwar Supergroup in Rajasthan contains sedimentary rocks from the late Cambrian, offering insights into ancient marine environments. Fossils of early arthropods and stromatolites in the Krol Formation (Himachal Pradesh) indicate India’s role in preserving Cambrian life.
Jurassic Period (201–145 Million Years Ago)
The Jurassic Period is renowned as the “Age of Dinosaurs”, with giants like Brachiosaurus and Stegosaurus dominating terrestrial ecosystems. The breakup of Pangaea accelerated, forming the Atlantic Ocean and creating varied habitats. Marine reptiles like Ichthyosaurs and early birds such as Archaeopteryx also emerged.
⦿ Tectonic Activity: The rifting of continents led to new ocean basins.
⦿ Flora: Gymnosperms like conifers and cycads thrived.
India’s Context: The Jaisalmer Basin in Rajasthan preserves Jurassic marine sediments with fossils of ammonites and marine reptiles. The Kutch Basin in Gujarat reveals dinosaur footprints and fossilized forests, highlighting India’s Jurassic ecosystems.
Cretaceous Period (145–66 Million Years Ago)
The Cretaceous Period witnessed the peak of dinosaur diversity and the rise of flowering plants (angiosperms). It ended with the Cretaceous-Paleogene (K-Pg) extinction, triggered by an asteroid impact and volcanic activity, which eradicated non-avian dinosaurs.
⦿ Biological Innovations: Evolution of social insects like bees.
⦿ Geological Events: Formation of the Deccan Traps, one of Earth’s largest volcanic provinces.
India’s Context: The Deccan Traps in west-central India, formed by massive lava flows, coincide with the K-Pg extinction. The Lameta Formation (Madhya Pradesh and Gujarat) contains dinosaur eggs and bones, including the carnivorous Rajasaurus narmadensis.
Quaternary Period (2.58 Million Years Ago–Present)
The Quaternary Period is defined by Ice Ages, the evolution of Homo sapiens, and the rise of human civilizations. Cyclical glaciations shaped modern landscapes, while the Holocene Epoch (11,700 years ago–present) saw the development of agriculture. The proposed Anthropocene Epoch reflects humanity’s profound environmental impact.
⦿ Climate Dynamics: Glacial-interglacial cycles influenced sea levels and ecosystems.
⦿ Human Impact: Deforestation, urbanization, and climate change define the Anthropocene.
India’s Context: The Siwalik Hills (Himalayan foothills) preserve fossils of early elephants, apes, and hominids. The Narmada Valley has yielded Homo erectus remains, linking India to human evolutionary studies. The Indian monsoon system, intensified by Himalayan uplift, shaped regional biodiversity and agriculture.
Conclusion
The Cambrian, Jurassic, Cretaceous, and Quaternary periods encapsulate pivotal moments in Earth’s history, from the explosion of life to the rise of humans. For UPSC aspirants, these periods underscore the interplay between geology, evolution, and climate, with India’s geological sites offering tangible links to global events. Mastery of these topics aids in addressing questions on paleontology, climatology, and sustainable development.
⦿ Interdisciplinary Relevance: Connects geology with anthropology, ecology, and climatology.
⦿ Policy Implications: Lessons from past extinctions inform biodiversity conservation strategies.