As has been mentioned earlier, fossils are considered as alphabets of the book of history of earth which provide very interesting information about the early history.
Fossils provide evidence of evolution and migration:
The fossils of most primitive animals and plants are preserved in the rocks, which were formed during the early part of the geological period of the earth while sedimentary rocks which were formed during later geological periods contain remains of more and more advanced forms of plants and animals indicating that more and more complicated and advanced animals and plants evolved from earlier ones.
A variety of organisms, though have been extinct since long from a particular region, newer and more developed types have flourished during subsequent periods in some other region indicating that along with their evolution the animals and plants have migrated from place to place on the surface of the globe.
The geological history of present day horses and their primitive ancestors may be taken as an example. The primitive horses originated in North America and in course of their evolution they migrated to India, through Central Asia. This type of scientific conclusion is possible because of systemic research on the available fossil records.
Fossils help in establishing the geological age and order of superposition of a sedimentary formation along with their correlation with the formations of one area with the other: Due to their gradual evolution the fossils of different organisms are found preserved within rock beds formed contemporaneously with the organisms.
The fossil assemblage of a rock bed is different from the bed above and below it. The rock-beds formed during different geological periods should contain fossil remains of those organisms which were flourishing during that particular geological period.
Hence, it is possible to establish the geological age of a particular bed and the chronological order of the sedimentary formation and correlate the same with other sediment formation formed elsewhere on the surface of the earth with the help of fossils.
Study of ancient geography:
Distinct differences are found among aquatic and land animals and plants. Shallow and deep water organisms differ from each other in many respects. The ancient organic world can be visualized in the light of their present day representatives. By examining the fossils and the rocks in which they are preserved, the rock beds formed under different climatic conditions and environments can be differentiated from each other.
Fossils of marine animals are found to be preserved in the rocks of the Himalayas indicating the presence of a sea in the region where the Himalayas is found today. Hence, by systematic study of the fossils the distribution of land and sea, changes in climatic conditions and such other ancient geographical features on the surface of the earth can be well established.
The search for new deposits of coal and petroleum:
The fossil fuel deposits are always associated with the ancient organic world. Most of the large deposits of coal are associated with the sedimentary rocks deposited in lake-basins during Permian period. On the other hand, petroleum deposits are commonly formed within marine sediments of Tertiary period.
Amber with ancient insects is used as jewellery. Hence, with the help of fossils, a geologist while establishing the age of the rocks of the area can locate fresh deposits of coal, petroleum and other useful rocks and minerals.
Apart from the above, the fossils are helpful in finding missing links of the animal and plant kingdom, which became extinct since long and in establishing a full picture of the organic evolution, fixing their geological age and working out a correct classification of the organic world and a standard geological time-scale.