Note on Fossils

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A fossil is the mark or hardened remains of a plant or animal that had existed thousands or millions of years ago. Some fossils such as leaves, shells or skeletons are preserved after the death of animals and plants. A fossil varies range from tiny microscopic to gigantic dinosaur bone in size. Most of the fossils are found in sedimentary rocks.

Identification of Fossils

Fossils can be identified by comparing its shapes, sizes and parts of organ. Some major methods to identify fossils are:

  1. Traces of dead bodies found on the sedimentary rocks are fossils. It may be a part or a whole body.
  2. A part of skeletal system or the whole skeleton system being preserved in sedimentary rocks is a fossil.
  3. A fossil may be in the form of molds or casts.
  4. Shells of animals, wood of plants, etc. can also be preserved in sedimentary rocks as fossils.

Process of Fossil Formation

The process with the help of which fossils are formed is known as fossilization. Any organism after their death may or may not be fossilized; it needs favorable situations to be fossilized. There are a number of factors that affects fossilization process. The major two factors that affect fossilization are:

  1. If the animal has hard parts, the chance of fossilization increases.
  2. The organism must be covered by protective materials shortly after the death.

There are many ways fossilization. Some of them are:

  1. The animals that live in or nearby water sometimes get covered by the sediment like mud, dirt and gravel and harden into rock. The hard parts of the body, like teeth and skeleton are preserved in their original form in the rock. It is then exposed at the surface of the Earth’s surface by geographical activities such as faulting and erosion.

  2. Some fossils are formed when animals are frozen in ice and preserved to the core.

  3. Organisms are also fossilized in the form of casts in sediments. The water inside the sediments dissolves the hard parts, leaving a hollow space in the sediment. The hollow shape is called mold; the space is then filled with minerals which harden to form a cast.

  4. Fossilization also occurs in the form of replacement of mineral inside of organic material of the dead bodies in sediment gets petrified i.e. turns into stone.

Except above mentioned methods, preservation of footprints of animals, tracing of leaves on sedimentary rocks, etc. are some other ways of fossilization.

Importance of Fossils

  1. Fossils provide evidence of living beings.
  2. Fossils help to know about the extinct animals and plants.
  3. Fossils show the history of the location from where a fossil is obtained.
  4. Fossil fuels such as coal and petroleum are the main sources of energy.
  5. Fossils help to make geological timescale.

Fossil Fuels

Fossil fuels are non- renewable sources of energy. Coal, petroleum and natural gas are the three categories of fossil fuels. They are formed from the dead bodies of living beings after millions of years. In these present days, fossils are being widely used in industries, vehicles, etc. as the main source of energy. But, the overuse of these fuels brings energy crisis and pollution in the environment.


Coal is a black or brown carbonaceous deposit which is found in the form of thick layer inside the earth and formed by plant fossils. It is taken out by mining. Its main components are: cellulose and lignin. Lignin forms from the wood of plants. Protein, oil, organic acid and salts are also found in it. Mainly, there are four types of coal.

S. No.

Types of Coal


Preselect Fossil


Weathering Properties

Other Properties







Weathers easily

Burns with smoke, loosely held particles


Sub- bituminous



Slightly hard

Weathers easily

Burns with less flame, waxy




Visible under microscope


Does not weather easily

Burns with blue frame




Black and shiny

Visible under microscope


Does not weather easily

Brittle, burns without smoke


Formation of Coal          

The exact process of formation of coal is still to be known, but on the basis of geographical evidence, we can consider that it is formed from plant fossils. Millions year ago, in carboniferous period, forest of coal plants grew in swamp of the earth. After the death of those plants, they feel into quite swamp water that protects them from rotting. Bacteria and geothermal energy changed some parts of the wood into gases that escaped out. The remaining black mixture containing mostly carbon was left that became a coal seam i.e. coal layer. In course of time, the increasing pressure from the overlying mud and sand squeezed out most of the liquid, leaving a pasty mass behind which slowly hardened into coal. In this way, coal was formed inside the earth. The layer of coal inside the earth may vary from some inches to several feet.

Importance of Coal

  1. Coal is used in industries, houses and i=other places for heating and generating electricity.
  2. Coal tar obtained from coal is used in the manufacture of plastic.
  3. Coal is used as fuel in steam engines to change water into steam.
  4. Coal is the main source of national economy in some of the countries.
  5. Coal is used for manufacturing petroleum and synthetic natural gas.

 Mineral Oil

The word petroleum is derived from the Latin word ‘petr’ which means “rock” and oleum which means “oil”. So, it is also called rock oil. Oil and natural gases together are called petroleum. Paraffin, fuel, lubricant oil, kerosene, natural gases and many other fuels are petroleum. Hydrocarbon covers almost 90 – 95% of the total and the rest part is oxygen, sulphur, nitrogen, etc.

Formation of Mineral Oil

The mechanism of the formation of mineral oil is open for speculation but scientists believe that petroleum was formed from dead bodies of plants and animals. After the death of plants and animals, they piled up on the sea bottom. In course of time, millions of tons of sand and mud cover them. Under pressure, the mud and sand changes into rock. The formed rocks create a very high pressure on the dead bodies. Because of high pressure at moderate temperature, scarcity of oxygen, and by the action of bacteria, the dead bodies were covered into a dark liquid trapped in the pore of the rocks, which is crude oil or petroleum. It takes millions of years to form crude oil. Thus, the petroleum is stored between two impervious layers of the rocks. The products that are obtained after refining of crude oil and their uses are listed below:

S. No.




Liquefied Petroleum Gas (L.P.G.)

Gas fuel, manufacturing of other organic chemicals


Petroleum ether

Solvent, cleaning



Vehicles fuel





Lubricant oil, Grease



Vaseline, Grease



Paraffin wax

Manufacturing of candle and matches


Petroleum cake, Bitumen asphalt

Fuel, construction of road





Importance of Mineral Oil

  1. Mineral oil is used as lubricant.
  2. Mineral oil is used as a fuel for cooking oil.
  3. Mineral oil is used in vehicles as a fuel.
  4. Mineral oil is used in many industries as fuel.
  5. Mineral oil such as black tar or bitumen is used in construction of roads.
  6. Mineral oil is used in manufacturing of plastics, chemical fertilizers, pesticides, paints, explosives, medicines, etc.

  1. The dead bodies of plants and animals hardened and preserved in sedimentary rocks are called fossils.
  2. All the remaining parts of the dead bodies are not fossilized. Following conditions are required to fossilize dead bodies:
    Hard parts of the organisms has more chance of fossilization.
    b. The part to be fossilized must be covered by protective materials, shortly after death.
  3. Tracing, mold, cast and remaining skeleton or parts of the dead bodies are forms of fossils.
  4. Fossils help to provide evidence of evolution, to make geological time scale and to determine the mines of coal and petroleum.
  5. Fossil fuels are non- renewable resources. Their main components are: coal and mineral oil.

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