The correct option is 1 only
Explanation
The study of the ocean floor configuration and the analysis of ocean floor sediments were critical developments in the mid-20th century that led to the formulation of the Sea Floor Spreading hypothesis and subsequently the Plate Tectonics Theory. These studies challenged the earlier notion that ocean basins were permanent and as old as the continents.
Statement-wise Analysis:
- Statement 1 is Correct: Before the extensive mapping of the ocean floor, scientists believed that ocean basins were permanent features formed early in Earth's history. Based on this assumption, it was expected that sediments accumulating over billions of years would form a very thick column on the ocean floor.
- Statement 2 is Incorrect: Radiometric dating of ocean floor rocks and sediments revealed that the ocean crust is much younger than the continental crust. Nowhere on the ocean floor was the sediment column or the underlying rock found to be older than 200 million years. In contrast, continental rocks can be over 3,000 million years old.
- Statement 3 is Incorrect: Contrary to the expectation of vast thickness, the actual observation was that the sediment layers on the ocean floor were unexpectedly thin. This thinness indicated that the ocean floor was relatively young and had not existed long enough to accumulate massive depths of sediment, supporting the theory that the ocean floor is constantly being created at mid-oceanic ridges and destroyed at trenches.
Key Takeaway:
The ocean floor is geologically young (nowhere older than 200 million years) and possesses a thin sediment layer, unlike the ancient and thick continental crust.