Magnetic stripes on the sea floor are caused in part by

The movement of the ocean's crust

When oceanic crust pulls apart magma rises to the surface at the mid-ocean ridges which then spills out to create new bands of rocks at the sea floor.

Explanation:

These magnetic strips and flips on the seafloor can be found due to the magma or the lava variations on the surface of the sea bottoms. The patterns that it develops in the ridges results in the form of a band of hard and soft like white and black rocks that magnetically vary in chemical-physical properties. These strips provide evidence of the movement and spread of lava and plate tectonic activities on the ocean floor. As the new rocks are created the alignment takes place and the global orientation of the new crust gets created. As deep oceanic valley forms part of the ridges it pushes the old rocks further below

Idont really understand

Then it is june the conclusion to the second sentence is just restating "if it is june then it is summer"