Q.Which one of the following facts was not considered by those while discussing the concept of sea floor spreading?

Sea floor spreading is the process where new oceanic crust is formed at mid-oceanic ridges and then moves away from the ridge. This concept was developed based on several key observations:

• Volcanic activity along the mid-oceanic ridges: This indicated that molten material was rising from the mantle, solidifying, and creating new crust.
• Stripes of normal and reverse magnetic field observed in rocks of the ocean floor: The symmetrical pattern of magnetic reversals on either side of the mid-oceanic ridges provided compelling evidence that new crust was continuously forming and moving outwards, recording the Earth's magnetic field at the time of its formation.
• Age of rocks from the ocean floor: Studies showed that rocks were youngest at the mid-oceanic ridges and progressively older with increasing distance from the ridges, confirming the continuous formation and outward movement of the oceanic crust. …

The concept of sea floor spreading revolutionized our understanding of how continents move and how Earth's crust is constantly recycled. Proposed by Harry Hess in the early 1960s, this theory suggested that new oceanic crust is continuously formed at mid-oceanic ridges and then moves away from these ridges, eventually being consumed back into the mantle at deep ocean trenches. This process provides the driving force for continental drift, which had been proposed earlier but lacked a convincing mechanism.

Scientists developed the concept of sea floor spreading based on several crucial observations and discoveries:

• Volcanic activity along the mid-oceanic ridges: These underwater mountain ranges are sites of intense volcanic activity. The presence of active volcanoes and the eruption of basaltic lava along these ridges indicated that new molten material was rising from the mantle and solidifying to form new oceanic crust. This was a direct observation supporting the idea of new crust being generated.

• Stripes of normal and reverse magnetic field observed in rocks of the ocean floor: One of the most compelling pieces of evidence came from studying the magnetic properties of rocks on the ocean floor. Scientists discovered a symmetrical pattern of magnetic stripes parallel to the mid-oceanic ridges. These stripes represented alternating bands of "normal" magnetism (where the magnetic field is oriented as it is today) and "reverse" magnetism (where it is oriented in the opposite direction). This pattern is a direct result of Earth's magnetic field periodically reversing its polarity, and as new crust forms at the ridge, it records the prevailing magnetic field at that time. As the crust spreads away, it carries this magnetic "signature" with it, creating a symmetrical record on either side of the ridge. This phenomenon acts like a geological "tape recorder," providing undeniable proof of new crust formation and movement.

• Age of rocks from the ocean floor: Further studies involved drilling into the ocean floor and dating the rock samples. It was consistently found that the rocks were youngest directly at the mid-oceanic ridges and progressively older as one moved further away from the ridges in either direction. This age progression perfectly matched the prediction of sea floor spreading: new crust forms at the ridge, and older crust moves away. …