Final answer:
The oldest seafloor fossils being younger than land-based fossils provides strong evidence for plate tectonics.
Step-by-step explanation:
The observations that the oldest fossils found on the seafloor are no more than about 180 million years old, while marine fossils in rock layers found in the Grand Canyon are 740 million to 1,200 million years old provide the best evidence for the principle of plate tectonics. This is because plate tectonics explains the movement of Earth's lithospheric plates, which can cause the seafloor to be constantly recycled through processes like subduction. As new seafloor is formed at mid-ocean ridges, older seafloor is pushed into subduction zones and destroyed.
This continuous process leads to the preservation of younger seafloor and the much older marine fossils found in rock layers on land. In conclusion, the age difference between seafloor fossils and land-based fossils is a strong indication of plate tectonics and the dynamic nature of Earth's crust.