Types of fossils include 4 different classes. Fossils can be defined as traces of ancient life. It can be of plants or animals. The main types of fossils include mold type, cast type and true form type. Fossils are preserved by natural processess. A simple definition of fossil is a tracess, impression or remnant of an organism of past ages that has been preserved in earth’s crust.
- Fossils includes bones, shells, hair etc.
- Body fossils represent all or a part of the body of any organism.
- Trace fossil shows evidence of an organism’s behaviour.
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Key terms: Fossils, Mold fossils, Trace fossils, Cast fossils, Organism, Substrate, Bones, Shells, hair
Types of Fossils
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Broadly there are 4 types of fossils that are known:
| Mold Fossils | A negative image of an organism preserved as a fossil in the substrate |
| Trace Fossils | When a mould is filled, a new substance is created |
| True Form Fossils | Fossilised nests, gastroliths, burrows, and footprints are all examples of prehistoric organic material |
| Cast Fossils | Anatomical or biological remains preserved in the fossil record |
Types of Fossils
The fossils can also be categorized into several other categories depending on the finer aspects. This classification is as follows.
Body Fossils
Body fossils, such as bones, shells, and leaves, are examples of the first type of fossil. These can be mold and cast fossils. For example, most of the fossilised dinosaur skeletons and large bones are body fossils. Replacement fossils, like petrified wood, or whole-body fossils frozen in ice or insects preserved in amber are another examples of body fossils.
Molecular Fossils
Biomarkers and biosignatures are terms used to describe molecular fossils. These are the end products of cellular biosynthesis that are incorporated into sediments and then into rocks over time. Several of these chemicals undergo well-known transformations and can remain stable for billions of years or longer.
Trace Fossils
Trace fossils are the traces of an animal or plant left behind after leaving an imprint. Nests, burrows, footprints, and other evidence of an animal's presence on Earth are all examples of trace fossils. The mineral form of the animal or plant is the main trace that left. The colours of the minerals that take the place of the original ones can be more beautiful. They can also be turned into art or jewellery.
Carbon Fossils
Carbon is a chemical element that is present in all living organisms.
- Toxic materials break down when an organism dies and is buried in sediment.
- During this, only carbon is left as a by-product.
- It is possible to see the delicate parts of plant like leaves in the thin layer of carbon.
- For instance, fern fossils that are 300 million years old.
Pseudofossils
Occasionally, watery solutions of various minerals rush through the sediments, taking the form of plant or animal parts. According to the place and form in which they are found, they're not classified as either plants or animals. Pseudo-fossils are the scientific term for these types of fossils.
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How Are Fossils Made?
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When living things (usually aquatic) die, they are buried quickly beneath sand, dirt, clay, or ash sediments.
- Normally, the soft parts decay or rot away, leaving the hard ones.
- As time passes, more sediment builds up.
- By applying heat, the sediments harden into a type of rock called sedimentary rock.
- The changes in the earth's crust pushes the sedimentary rock layers upwards .
- The fossils are re-exposed to the surface as a result of erosion caused by wind, rain, and other elements.
The various ways by which organism turns into fossil is given below.
Unaltered Preservation
A hardened form of tree sap is similar to amber within which it has been trapped with insects or plants.
Permineralization Or Petrification
Rock-like minerals slowly seep into the organic tissues and replace them with silica, calcite, or pyrite.
- It forms a fossil that looks like rock.
- It's capable of preserving both hard and soft parts.
- Permineralization affects the majority of the bones and wood fossils.
Replacement
Minerals such as calcite, silica, pyrite, and iron dissolve and replace an organism's hard parts.
Carbonization or Coalification
Only the carbon is left in the specimen after the coalification. It is necessary to remove other elements such as hydrogen, oxygen, and nitrogen.
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Things to Remember
- There are 4 main types of fossils.
- Various types of fossils are mold, cast, trace, and true form fossils.
- Fossils are formed when dead remnants of living things gets heat and pressure over a long period of time.
- There are many different methods in which organisms turn into fossils.
- Some of them includes unaltered preservation, permineralization,carbonisation and replacement.
- On the basis of finer charecteristics, fossils can be of 5 types.
- These includes body, molecular, trace, carbon and pseudofossil.
Sample Questions
Ques. What is a Fossil? (1 mark)
Ans.: When organisms partially or completely get mineralized and get preserved as a type of mould naturally or by human interference then such mould or cast is called a fossil.
Ques. What kind of information a Fossil provides? (1 mark)
Ans. A fossil provides a palpable proof regarding the historic life that may have been nurtured on the planet before the emergence of humans or during the time of early humans and the evolution there on.
Ques. What is meant by fossilization and what are the optimal conditions for fossilization to take place? (2 marks)
Ans. The process of formation of fossils of the dead organisms is termed as fossilization. For fossilization to take place it is necessary that the organism is buried as soon as possible after its death in a site which is rich in sediments and mineral and moisture rich soil. The organism may be buried naturally or by human interference.
Ques. What is meant by petrification? (2 marks)
Ans. Petrification or mineralization is a process of replacing the original remains of the dead organism with specific minerals which needs to be present in sufficient quantities in dissolved forms near the remains. Most commonly found minerals during mineralization are Calcium Carbonate, Silicon Dioxide etc.
Ques. What are Chemofossils? (1 mark)
Ans. During the process of Fossilization, it sometimes happens that only the constituent chemicals are left behind, these chemicals are seen as organic molecules and like typical fossils they are proof of ancient life, such fossils are called Chemofossils.
Ques. What is the body fossil? (1 mark)
Ans. Body fossils are the first type of fossils. They can be mold or cast fossils. For example, bones, shell, leaves etc are body fossil or animal and plant.
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