Are all the rocks on the earth the same ones that have always been there, or do we get new rocks sometimes?
In: Earth Science
They’re made of the same material that’s always been here (minus an incredibly small amount of material that falls to earth as meteors). There’s something called the rock cycle, in which rocks change form due to different geological processes, including melting.
Igneous rocks = rocks that are formed when magma or lava cools and solidifies. e.g. granite, basalt, obsidian.
Metaphoric rocks = rocks that are transformed from one type of rock into another due to conditions like high pressure or heat — not enough to melt, but enough to change crystal structures. e.g. gneiss, shale, slate.
Sedimentary rocks = rocks that are formed by the consolidation of sediment, like silt or sand. ion-heavy water flows between the grains and deposits new minerals, solidifying the structure into a new solid rock. e.g. sandstone, limestone, shale.
The sediment could have either biologic origins, such as mud, or geologic origins, such as wind and water eroding existing rocks.
Existing rocks are pushed underground by plate tectonics, which cause them to melt into magma once deep enough. Then, they can rise back up through the crust and solidify embedded there, or escape to the surface through a volcano and solidify there.
All rocks are made of combinations of minerals, and they can shift from type to type, into new kinds of rocks, due to the processes above.
EDIT: To expand on where the minerals that make up rocks came from in the first place:
The solar system was formed from a cloud of gas and dust. Lots of it, namely hydrogen, coalesced into the sun, but lots of it remained in orbit around the sun and coalesced into planets (and moons and asteroids). The heavy (mainly heavier than hydrogen and helium) elements that make up rock minerals were formed either in the late life stages of prior stars’ lives, or when they exploded in supernovae.
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