The surface of the Earth is composed of a mosaic of tectonic plates with edges that create fault lines. The Earth's crust is made of seven major plates and several smaller plates. As the plates move, new sea floor can be created. The plates form three different kinds of boundaries: convergent, divergent, and transform. Convergent boundaries are also called collision boundaries because they are areas where two plates collide. At transform boundaries, the plates slide and grind past one another. The divergent boundaries are the areas where plates are moving apart from one another. Where plates move apart, new crustal material is formed from molten magma from below the Earth's surface. Because of this, the youngest sea floor can be found along divergent boundaries, such as the Mid-Atlantic Ocean Ridge. The spreading, however, is generally not uniform causing linear features perpendicular to the divergent boundaries, shown in this dataset as contour lines.

This dataset shows the age of the ocean floor with the lines or contours of 5 million years as shown in the colorbar. Plate names and plate boundaries are available as layers but must be turned on to appear. The data is from four companion digital models of the age, age uncertainty, spreading rates and spreading asymmetries of the world's ocean basins. Scientists use the magnetic polarity of the sea floor to determine the age. Very little of the sea floor is older than 150 million years. This is because the oldest sea floor is subducted under other plates and replaces by new surfaces. The tectonic plates are constantly in motion and new surfaces are always being created. This continual motion is evidenced by the occurrence of earthquakes and volcanoes.