At some point, Earth became the hiding place of the Blue Lion after the Lions of Voltron were scattered across the universe to keep them from Emperor Zarkon and the Galra Empire. The native people of the area in which it was hidden were aware of it, and inscribed various legends surrounding the Lion into the walls of the surrounding caverns. At some point at least one member of the Galra species apparently visited Earth and was the ancestor of Keith. Earth's government would also form the organization known as Galaxy Garrison for the purposes of space exploration and planetary defense.
The Blue Lion was eventually discovered after Shiro escaped from Galra captivity and made his way back to Earth, where he was found by Galaxy Garrison personnel but freed by Keith and three others. The five would subsequently depart the planet using the Blue Lion, escaping a Galra warship in the process.