It's impossible to give an exact percentage for the surface area covered by mountains, as there's no universally agreed-upon definition of what constitutes a "mountain."

Here's why:

* No clear definition: What's considered a mountain varies. Some define it by elevation (e.g., anything over 1,000 feet), while others use other criteria like topographic prominence or slope.

* Terrain variation: Mountain ranges can be vast, with intermingling plateaus, valleys, and foothills. Deciding where a mountain "ends" can be subjective.

* Data limitations: Accurately mapping and quantifying every mountain range across the Earth's surface is a complex task.

However, we can provide some general estimates:

* Roughly 24% of the Earth's land surface is at an elevation of 1,000 meters or higher. This includes mountains, plateaus, and other high-altitude terrain.

* Estimates for mountain ranges specifically range from 5% to 15% of the Earth's surface.

Keep in mind these are approximate figures, and the exact percentage will depend on the specific definition of a "mountain" used.