Correct Option
The correct option is 2 and 3 only.
Explanation
The Convection Current Theory was introduced to explain the mechanism or force driving the movement of continents, addressing a major limitation in the earlier Continental Drift Theory. It postulates that thermal convection currents in the mantle drag the overlying lithospheric crust.
Statement-wise Analysis
- Statement 1 is Incorrect. The Convection Current Theory was proposed by Arthur Holmes in the 1930s. Alfred Wegener proposed the Continental Drift Theory (1912) but failed to explain the driving force convincingly, suggesting instead the "pole-fleeing force" and "tidal force," which were later rejected.
- Statement 2 is Correct. Holmes suggested that convection currents are generated due to radioactive elements causing thermal differences within the mantle. The heat generated creates rising limbs of currents that diverge at the surface and descending limbs where the crust sinks.
- Statement 3 is Correct. According to Holmes, this system of currents operates in the entire mantle portion. This was an attempt to provide a comprehensive explanation for the forces capable of moving massive continental blocks.
Key Takeaway
Key Takeaway: Arthur Holmes' Convection Current Theory (1930s) identified mantle convection driven by radioactive heat as the force behind continental drift, replacing Wegener's weaker gravitational and tidal force hypotheses.