I'm not sure it's what you're looking for, but I found Fractal Terrains 3 to be quite useful. The full version is about $40 USD plus tax, but there's a free trial available on the ProFantasy website here, so you can get a feel for it without having to pay anything. And if you're curious: no, I don't work for them, but I have bought a handful of their products.
The software itself is intended to draw world maps, and is quite useful for the purpose. It allows random generation of worlds via several fractal algorithms (hence the name), and you can make your own adjustments as well.
Finer detail generally requires supporting software (namely Campaign Cartographer 3, another $45; ProFantasy does offer various bundles if you find yourself interested in their products, but that's dependent on what level of detail you want your maps to have; for just a world map, those two will be more than enough), but it's perfectly capable of editing mountain ranges, coastlines, etc., which is plenty for a full-world map. It can't do tectonic plates, as far as I'm aware, so you might need to look elsewhere for that or else draw multiple maps manually. Fractal Terrains 3 supports some two dozen projections, such as Mercator, equirectangular, etc.; you want to draw on a sphere, so the orthographic projection would be your best bet. It can export to multiple formats, including Google Earth files, so you have plenty of options there.