Question

Fossils are generally found in
A. Sedimentary rocks
B. Igneous rocks
C. Metamorphic rocks
D. Any type of rocks

Answer 1

Hint:
- Geomorphic agents such as wind and water work in the formation of these types of rocks.
- These rocks cover about 75 percent of the surface area of the globe.
- These rocks are found in different layers and the fossils present here help to find out the age of the rock.

Complete answer:
A. Sedimentary rocks: these are also called as layered or sedimentary rocks. When the sediments get aggregated and compacted they form sedimentary rocks. These sediments come from the older rocks, plant and animal remains and therefore they contain animal and plant fossils. Erosion and deposition of these sediments are done by the geomorphic agents such as wind and water.

B. Igneous rocks: they are also called the primary rock. Its name finds its root in the word 'ignis' which is a Latin word whose literal meaning is fire. These are formed when the molten material, which is magma and lava, gets cool, solidified and crystallized and because of this process of formation any fossils of plants and animals are not found in them. As because of the very high temperature of magma and lava the remains are destroyed.

C. Metamorphic rocks: the word 'metamorphose' means a change in form. Thus in metamorphic rocks, complete alteration of the pre-existing rock takes place. Reason for this alteration is high temperature and pressure. Thus rocks which have been changed either in form or composition without disintegration are known as metamorphic rocks.

D. From the above explanation it is clear that not all the types of rocks contain fossils. Thus this option is incorrect.

Therefore, the correct answer is A

Note:
- Though sedimentary rocks cover about 75 percent and the remaining 25 percent is covered by igneous and metamorphic rocks. But despite this sedimentary rocks constitute only 5 percent of the whole crust and the remaining 95 percent is formed by igneous and metamorphic rocks.
- Igneous rocks have almond-shaped vesicles which are known as Amygdales. These are bubbles which are formed due to the escape of gases and are filled with secondary minerals.