I want to rotate earth about z axis but it gives me error that object is not 3d Graphics
Use Show rather than Graphics3D
You apply GeometricTransformation to the primitives of Planet, that you extract with [[1]]:
GeometricTransformation
Planet
[[1]]
Graphics3D[ GeometricTransformation[Planet[[1]], RotationTransform[Pi/3, {0, 0, 1}]]]
Sorry, this is the right answer I didn't quite understand what was done