Extracting earth surface

Your questions are about the full Google Earth application and
SketchUp.
However this is the group for the Google Earth Plug-in Api.
You would probably get more help in either of the groups for these
products.

www.google.com/support/forum/p/earth?hl=en

groups.google.com/group/sketchup/

That said the terrain is imported in two parts – as an image and a
mesh.
The output format is determined by the user – common formats are
.skp, .obj, .max

Hope that helps.

F.