Earth

This animated diagram illustrates seafloor spreading on Earth.
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Image courtesy of NOAA/NESDIS/National Geophysical Data Center, Boulder, CO.

This animation shows how seafloor spreading works on Earth. The age of the ocean floor in the Atlantic and Pacific Oceans is shown in colors. The animation shows that the American continents are separated from the Eurasian and African continents as time advances. The red sections are the youngest portions of the ocean floor, where fresh new crust is added from the deep interior of the Earth. The blue portions are the oldest and are near regions of the Earth where subduction is taking place.

The red regions in the animation are associated with mid-ocean spreading ridges. These are areas of the Earth's crust where the ocean floor is being forced to spread apart. The continents drift along on top of the crust as it spreads apart.

Mars

This is a map of the entire Martian surface.
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Image courtesy of NASA.

As the map above shows, the elevated areas of the Martian surface (colored in red) are concentrated on the southern hemisphere of Mars. This would suggest that a single, large plate has formed on Mars, with no subsequent plate tectonics.