This is a significant portion of the planet, and it's important to remember that:

* Most sedimentary rocks are relatively young: They form from the weathering and erosion of older rocks, and thus are typically found on the surface or in relatively shallow layers.

* Sedimentary rocks are crucial for understanding Earth's history: They hold fossils, which are the remains of ancient life, and can provide clues about past environments and climates.

However, it's important to note that this number is a general estimate. The exact percentage can vary depending on:

* The definition of "surface": Are we talking about the land surface only, or the entire Earth, including the ocean floor?

* The specific location: Some areas, like the Himalayas, are primarily composed of metamorphic or igneous rocks, while others, like the Great Plains, are dominated by sedimentary rocks.

Overall, sedimentary rocks are a significant component of the Earth's surface and play a crucial role in understanding its history and processes.