Continental Drift | Geology Optional Notes for UPSC PDF Download

Continental Drift Theory

The theory of continental drift proposes that the Earth's continents have not always been in their current positions but have moved over geological time scales.

• Early Pioneers
  • F.B. Taylor, an American physicist, initiated the theory in 1910.
  • Alfred Lothar Wegener, a German meteorologist and geophysicist, is credited as the pioneer, suggesting the theory in 1912.
• Wegener's Contributions
  • Wegener introduced the concept of Pangaea, a supercontinent, and Panthalassa, an oceanic counterpart.
  • He observed geological data, continuity of structures, stratigraphic formations, and fossil distribution as evidence.
  • Wegener's observations included widespread glaciation in the Permo-Carboniferous era.
• Evidence and Support
  • Geological data, including rock formations and structures, supported Wegener's theory.
  • The distribution of fossil fauna and flora across continents provided further evidence.
  • Glacial evidence supported Wegener's observations of past climates and continental positions.
• Challenges and Criticisms
  • Critics questioned the mechanism behind continental drift, particularly the forces required to move large landmasses.
  • Wegener faced skepticism and rejection from the scientific community.

• Continued Research
  • Wegener continued to gather evidence in support of his theory until his death in 1930.
  • Alexander Du Toit proposed the breakup of Pangaea into Laurasia and Gondwanaland in 1937.

Pangaea and Supercontinents

Pangaea was the supercontinent proposed by Wegener, meaning "all lands" in Greek.
It consisted of all present-day continents fused together.

• Laurasia and Gondwanaland
  • Alexander Du Toit proposed the breakup of Pangaea into Laurasia and Gondwanaland.
  • Laurasia included North America, Greenland, Europe, and parts of Asia.
  • Gondwanaland consisted of South America, Antarctica, Africa, Madagascar, India, and Australia.
• Continental Breakup
  • Laurasia and Gondwanaland eventually broke apart into the continents we recognize today.
  • The breakup led to the formation of separate landmasses with distinct geological features.

Palaeo-Tethys Ocean

• Formation
  • The Palaeo-Tethys Ocean separated Laurasia and Gondwanaland.
  • It formed as a result of the continental breakup.
• Etymology
  • The name "Palaeo-Tethys" comes from the Greek goddess of the sea, Tethys.

Maps showing drift of continents from Pangaea to present

This structured explanation covers the key points regarding the theory of continental drift, the concept of Pangaea and supercontinents, as well as the Palaeo-Tethys Ocean, providing a comprehensive understanding of the topic.

Evidences of Continental Drift

1. Geometrical Reconstruction
   • If one cuts out the continents from a world map and reassembles them, they fit together like a jigsaw puzzle.
   • This suggests that the continents were once connected and have since drifted apart.
2. Geological Evidences
   • Coastlines on opposite sides of the Atlantic Ocean share similarities in lithology, stratigraphy, fossil content, and tectonic structures.
   • For example, rocks in Brazil closely resemble rocks in Africa, indicating a shared geological history.
   • Mountain belts terminate on one coastline and continue on another landmass across the ocean.
3. Palaeoclimatic Evidences
   • Glacial evidence from the Carboniferous period is found on continents now widely separated.
   • Glaciation patterns on South America, southern Africa, Madagascar, India, Australia, and Antarctica suggest they were once joined as a single landmass.
4. Palaeontological Evidences
   • Fossils of land plants like Glossopteris and Gangamopteris are found across Africa, Australia, and India, indicating past connectivity.
   • These plants couldn't have dispersed across oceans, suggesting a shared landmass.
5. Sea Floor Spreading
   • Sea floor spreading refers to the expansion of oceanic crust.
   • Studies confirm that continents were once part of a supercontinent, Pangaea, which later broke apart.
   • The ocean floor between continents has spread over the past 200 million years.
6. Palaeomagnetic Evidences
   • Palaeomagnetic studies examine Earth's magnetic field over geological time.
   • Mid-Oceanic Ridges (MORs) preserve magnetic records in basalt rocks.
   • Newly formed basaltic lava retains the magnetic polarity of Earth at the time of solidification.
   • Magnetometer surveys over ocean floors reveal strips of normal and reversed polarity, suggesting changes in Earth's magnetic field.
   • Alternating bands of normal and reversed polarity parallel to MORs indicate magnetic anomaly strips.
   • This supports the theory of sea floor spreading and continental drift.
   • Polar wandering and reversals in Earth's magnetic field indicate that continents were once joined and have since drifted apart.
   • This detailed explanation covers the various lines of evidence supporting the theory of continental drift, including geometrical reconstruction, geological, palaeoclimatic, palaeontological, sea floor spreading, and palaeomagnetic evidences.

Forces Responsible for Drifting of Continents

Wegener's Concept

• Alfred Wegener proposed that continents are primarily composed of lighter material known as 'SiAl' (silicon and aluminum) that floats over denser rock material called 'SiMa' (silicon and magnesium).
• Wegener attributed the drifting of continents to gravitational forces exerted by the Sun and Moon or tidal forces in the ocean.
• However, this concept was rejected due to the insufficient magnitude of tidal forces to cause continental drift.

Holmes's Convection Current Concept

• In 1928, Arthur Holmes introduced the idea of thermal convection in the mantle as the driving force behind continental drift.
• He suggested that convection currents are generated by radioactive heating within the Earth's interior.
• Despite its proposal, this concept couldn't gain traction as the amount of radioactive heating is considered insufficient to cause significant movement of continents.
• Wegener and Holmes's ideas, though rejected, laid the groundwork for modern theories of continental drift.

Plate Tectonic Theory

• Wegener's theory lacked a satisfactory explanation for the forces driving continental drift.
• Plate tectonic theory emerged to address this gap, considering the role of convection currents but in a different manner than Holmes proposed.
• Plate tectonics theory, discussed in detail in subsequent units, provides a comprehensive framework for understanding the mechanism behind continental drift.
• It incorporates the movement and interaction of lithospheric plates driven by mantle convection currents, leading to the drifting of continents.
• This elaboration covers the historical perspectives and modern theories regarding the forces responsible for continental drift, including Wegener's concept, Holmes's convection current concept, and the Plate Tectonic theory.