Almost exactly the same size

But the comparison stops there.

Where earth's moon is pretty much stone dead geologically, Io is the most geologically active body in our solar system.

Its 400 active volcanoes are fueled by a constant supply of heat generated by friction between constituent rock layers due to intense tidal forces. The tidal forces are due to its close proximity to the very massive Jupiter and to a lesser extent, the other three large moons in the system.

By Apollo 17 Picture of the Whole Earth: NASA Telescopic Image of the Full Moon: Gregory H. Revera True color image of Io: NASA / JPL / University of Arizona - The Earth seen from Apollo 17.jpg FullMoon2010.jpg Io_highest_resolution_true_color.jpg, Public Domain, Link