The earth where we humans live, the ocean accounts for about 71% of its total surface area, and the land accounts for about 29% of its total surface area.Oceans are made of water, while land is mostly made of rock.So what is a "rock"? In a broad sense, "rock" refers to both those relatively hard stones, as well as those naturally occurring loose "sand mud" and volcanic debris.In a narrow sense, rock mainly refers to the part with relatively hard texture, that is, stone. Rocks can be roughly divided into three categories according to the reasons for their formation: 1. "magmatic rock" or "igneous rock"; 2. "sedimentary rock"; 3. "metamorphic rock".These three major rocks are the main materials that make up the earth on which human beings live.Among them, sedimentary rocks account for the largest proportion, accounting for about 3/4 of the surface area, and the proportion in China is even higher, accounting for about 77% of the total area.From this we can say that the sea is supported by the land, and the land is supported by the rocks.Rocks are not only an important part of the earth, but also the backbone of the earth.Without rocks, there would be no Earth.

Stone is also essential for stone carvings and grottoes.If there were no stones, there would be no science of stone carving, let alone the art of grottoes.