Where do the rocks on the earth come from?
There are rocks everywhere on the earth. In some places, the surface layer is sediment, and the bottom layer is rock; There are rivers and oceans, and there are rocks under the water layer. Rock is like a hard shell, tightly wrapped around the earth. People call it the lithosphere. The thickest part of the lithosphere exceeds 100 km. In other words, not only the crust is made of rocks, but also the top of the mantle.
Why are there so many rocks on the earth?
It turns out that all rocks were gradually formed during the evolution of the earth.
According to the different formation of rocks, we can divide all rocks into igneous rocks, sedimentary rocks and metamorphic rocks.
Igneous rock is the main body of the earth's lithosphere. All the rocks at the top of the mantle and about 3/4 of the rocks in the crust belong to igneous rocks. Igneous rocks are formed by the cooling and solidification of hot molten magma. Although there are volcanic rocks covering tens of thousands of square kilometers and thousands of meters thick in some places, the proportion is still very limited, and most of them are formed by magma that failed to erupt to the surface and solidified directly in the deep underground. This is called igneous rock, such as widely distributed granite.
Rocks formed in history (including igneous rocks, sedimentary rocks and metamorphic rocks) will be weathered and eroded after exposed to the ground, and gradually transformed into sediments and chemical decomposition products. These sediments and chemical decomposition products are transported by wind, water or glaciers, and eventually accumulate and precipitate in lake basins or other depressions. After long-term compaction and cementation, as well as the influence of heat in the earth, they re-solidify into rocks, which are sedimentary rocks, such as sandstone cemented with sand grains and shale piled with mud. In the process of the formation of sedimentary rocks, there are often organisms involved, so fossils composed of paleontological remains or remains can also be found in sedimentary rocks.
In the evolution of the earth, rocks are subjected to intense extrusion, dislocation or high temperature, or injected with foreign substances, thus completely changing their appearance and forming a new kind of rock, which is metamorphic rock. For example, granite will become gneiss, and some sandstone and shale will become slate and schist.
In short, all kinds of rocks on the earth are gradually formed through the above three ways.