Que. What do you understand by the theory of ‘continental drift’? Discuss the prominent evidences in its support.
‘महाद्वीपीय विस्थापन’ के सिद्धान्त से आप क्या समझते हैं? इसके पक्ष में प्रमुख साक्ष्यों की विवेचना कीजिए।
Structure of the Answer
(i) Introduction: Define the “theory of continental drift” within the historical and scientific context, highlighting its revolutionary nature in one clear line.
(ii) Main Body: Break down the theory’s core components and discuss the most significant global historical evidence, including advancements in scientific methods.
(iii) Conclusion: Highlight the lasting impact of the theory on both historical and geological understanding, linking it to broader scientific progress.
Introduction
The “theory of continental drift” by Alfred Wegener in 1912 transformed scientific thought, proposing that Earth’s continents were once a single supercontinent, “Pangaea”, which gradually fragmented and drifted apart.
Historical Genesis and Context of the Theory
(i) Influence of early explorers: European explorers during the Age of Discovery (15th-17th centuries) noticed the puzzle-like fit between the coastlines of South America and Africa, sparking speculation of their prior connection.
(ii) Alfred Wegener’s pioneering contribution: In 1912, Wegener formalized these early ideas into the “theory of continental drift”, challenging long-standing scientific notions of a static Earth. His theory was based on multi-disciplinary evidence from geology, paleontology, and climatology.
(iii) Resistance and skepticism: Despite its revolutionary nature, the theory was initially met with widespread resistance due to the absence of a convincing mechanism explaining “continental movement”, as existing geological models adhered to the “fixist” belief that continents were stationary.
(iv) Paleontological findings supporting Wegener: Early 19th-century paleontologists, such as Georges Cuvier, discovered identical fossils of extinct species on now-separated continents, further supporting the idea of a historical connection between these landmasses.
(v) Wegener’s evidence from historical climatology: Wegener also relied on evidence of historical climatic changes, noting that coal deposits and tropical plant fossils found in Antarctica indicated that it was once closer to the equator, supporting his drift hypothesis.
Prominent Geological and Paleontological Evidence
(i) Fossil distribution across continents: Fossils of the freshwater reptile “Mesosaurus” were found in both South America and Africa. This distribution is key evidence that these continents were once joined, as the species could not have crossed vast oceans.
(ii) Mountain chain continuity: Geological structures, such as the Appalachian Mountains in North America and their extension in Scotland, reveal an identical geological history, indicating that these regions were connected in the past as part of “Pangaea”.
(iii) Glacial striations and deposits: Evidence of identical glacial deposits from the same time period was found in South America, Africa, India, and Australia, suggesting that these continents were once situated near the South Pole before drifting apart.
(iv) Distribution of coal deposits: Large coal deposits in regions such as Siberia and Antarctica suggest that these areas were once part of warm, tropical environments, further corroborating the theory of drifting landmasses over millions of years.
(v) Evolutionary divergence: Paleontological studies of species like “Glossopteris” (a plant fossil found in South America, Africa, Antarctica, and India) demonstrate that continental drift led to species evolving in isolated environments, contributing to global biodiversity.
Advances in Scientific Methods Supporting Continental Drift
(i) Discovery of sea-floor spreading: In the mid-20th century, scientists discovered the process of “sea-floor spreading”, which provided the much-needed mechanism to explain how continents drifted apart. This discovery occurred at mid-ocean ridges, where new crust is formed as tectonic plates move.
(ii) Paleomagnetic studies: The development of “paleomagnetism” in the 1950s offered critical support for the theory. Paleomagnetic data showed that rocks retain a record of Earth’s magnetic field at the time of their formation. As continents drifted, these magnetic records shifted, providing clear evidence of continental movement.
(iii) Plate tectonics: The theory of “plate tectonics”, formulated in the 1960s, expanded on Wegener’s ideas by explaining how continents drifted due to the movement of large “tectonic plates” across Earth’s surface. This theory unified various geological observations and finally provided a comprehensive model for continental drift.
(iv) Seismic and volcanic activity: Advances in seismology further supported the theory. Scientists discovered that earthquake zones and volcanic activity were often concentrated along tectonic plate boundaries, offering additional evidence of plate movement.
(v) Modern satellite measurements: In the late 20th and early 21st centuries, GPS technology has allowed scientists to directly measure the movement of continents. These measurements confirm that continents are still drifting apart at measurable rates, such as North America moving away from Europe by several centimeters per year.
Continental Drift’s Impact on Global Scientific Understanding
(i) Revolution in Earth sciences: The acceptance of the “theory of continental drift” revolutionized the field of geology, marking a shift away from earlier static models of Earth’s surface. It laid the foundation for modern “plate tectonics”, fundamentally altering our understanding of the Earth’s dynamic processes.
(ii) Historical climate understanding: The theory also provided a framework for understanding the shifting positions of continents over geological time, explaining past climate changes and the distribution of climatic zones throughout history.
(iii) Impact on world history: From the distribution of ancient human civilizations to the spread of flora and fauna, continental drift helped explain how the physical arrangement of continents influenced the evolution of species and the migration of human populations.
(iv) Role in understanding natural resources: The theory also informed the study of natural resource deposits, such as oil and coal. It explained how the movement of landmasses created conditions for the formation of these resources in specific regions over millions of years.
(v) Shaping environmental policy: The realization that continents are constantly moving has influenced global environmental and conservation policies. It underscores the need for understanding Earth’s geological history to address present-day environmental challenges, such as climate change and habitat conservation.
Conclusion
The “theory of continental drift” reshaped geological thought, offering a transformative explanation for the movement of continents. Its scientific acceptance revolutionized our understanding of Earth’s historical processes and global evolution.
