Question

Why are sedimentary rocks the only rock type to contain fossils?

Answer 1

Hint: The method of formation of different types of rocks contains a great deal of information about the kinds of material that they can hold. The drastic temperature and pressure conditions associated with different rock types decide whether they can contain organic matter or not.

Complete answer:
The fossils are nothing but the dead and decaying organic matter that slowly decomposes inside the earth’s crust and leads to the formation of various minerals and fuels over millions of years.
The remains of plants, animals and all forms of life begin to degrade when they are buried and are collectively called fossils.
Rocks like igneous rocks that find their origin deep inside the earth’s crust where the hot magma and material from volcano eruptions slowly transforms into these rocks. It is practically impossible for organic matter like fossils to survive such drastic conditions and therefore igneous rocks do not contain fossils in them
Sedimentary rocks are formed on the Earth’s surface and not deep inside its crust. These rocks are formed under water at low temperatures and pressure and are suitable to store organic matter.
 Thus, sedimentary rocks contain fossils due to the ambient physical conditions that allow organic matter to be preserved over time.

Note:
The metamorphic rocks are actually formed from the breaking down of igneous and sedimentary rocks only but they are incapable of containing fossils as the conditions to which they are exposed brings a lot of changes and the fossils cannot be preserved in such conditions.