The correct option is 1 and 3 only.
Explanation
The theory of Sea Floor Spreading, proposed by Harry Hess in the early 1960s, postulates that new oceanic crust is continuously formed at mid-oceanic ridges through volcanic activity and then moves away from the ridge. This theory provided the mechanism for continental drift and became a cornerstone of Plate Tectonics.
Statement-wise Analysis:
- Statement 1 is Correct: Studies of paleomagnetism reveal that rocks equidistant on either side of the mid-oceanic ridge crest exhibit remarkable symmetry in their magnetic properties (magnetic anomalies). This "magnetic striping" records reversals in the Earth's magnetic field, proving that the crust on both sides formed simultaneously and spread laterally.
- Statement 2 is Incorrect: The age of the oceanic crust is not uniform. The rocks are youngest at the crest of the mid-oceanic ridge (where new magma solidifies) and the age increases as one moves away from the crest towards the trenches. The statement incorrectly suggests that age decreases away from the ridge.
- Statement 3 is Correct: The depth of earthquake foci provides evidence for the movement of oceanic plates. While mid-oceanic ridges (divergent boundaries) experience shallow-focus earthquakes, deep oceanic trenches (convergent boundaries) are characterized by deep-seated earthquake occurrences (Wadati-Benioff zones). This indicates the subduction of the oceanic lithosphere deep into the mantle.
Key Takeaway:
The primary evidences for Sea Floor Spreading are the increasing age of rocks away from ridges, the symmetry of magnetic stripes across ridges, and the variation in earthquake depth from ridges (shallow) to trenches (deep).