It's difficult to give a precise percentage of Earth's surface covered by mountains because there's no universally agreed upon definition of what constitutes a "mountain." However, we can make some estimations based on different approaches:

1. Elevation:

* If we consider areas above 500 meters (1,640 feet) as mountains, then approximately 24% of Earth's land surface is covered by mountains.

2. Topographic Relief:

* If we consider areas with significant topographic relief (difference in elevation) as mountainous, then the percentage might be higher, potentially reaching 30% or more.

3. Mountain Ranges:

* The world's major mountain ranges, including the Himalayas, Andes, Rockies, and Alps, cover a substantial portion of Earth's land surface. These ranges alone account for a significant portion of the overall mountain coverage.

Important Considerations:

* Varying Definitions: The definition of a mountain can be subjective, making it difficult to establish a definitive percentage.

* Land vs. Water: We're primarily talking about land areas here. The ocean floor has its own features, including underwater mountain ranges and volcanoes.

* Regional Differences: Mountain coverage varies considerably across different continents and regions.

In summary:

While it's not possible to provide an exact figure, a reasonable estimate is that around 24-30% of Earth's land surface is covered by mountains, depending on the definition used.