What is Fossil?
Fossil, which is also called impression, remnant, or trace of a plant or an animal of a past geologic age, which has been preserved in the crust of the Earth. The complex of data that is recorded in fossils across the world is called the fossil record. It is the major source of information about the history of life on Earth.
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About Fossil
Only a lesser fraction of the ancient organisms can be preserved as fossils, and usually, only organisms that contain a resistant and solid skeleton are preserved readily. Most of the primary groups of invertebrate animals have a calcareous shell or skeleton (for example, molluscs, corals, bryozoans, brachiopods, and more). The other forms contain shells of calcium phosphate (which also takes place in the vertebrate’s bones) or silicon dioxide. A bone or shell that is quickly buried after the deposition can retain these organic tissues, though they become petrified (which are converted to a stony substance) over time. Unaltered hard bits, such as brachiopod or clamshells, are relatively abundant in sedimentary rocks, some of which are very old.
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Parts of Fossil
The hard parts of the organisms that become buried in sediment can be subjected to a variety of other changes at the time of their conversion to solid rock, however. Solutions can fill the pores or interstices of the bone or shell with calcium carbonate or the other mineral salts and hence fossilize the remains, in a process referred to as permineralization. In the other example, the initial skeletal material will be fully replaced by other mineral matter, a method known as substitution or mineralization. In other cases, circulating acid solutions remove the original shell but leave a void in its place, which siliceous or circulating calcareous solutions may fill with a new matrix, resulting in a new image of the original shell.
In contrast, the soft parts of the plants or animals are very rarely preserved. The preservation of carcasses of Pleistocene mammoths in the ice and the embedding of insects in the amber (which is a process known as resin fossilization) are rare, but they are striking examples of fossil preservation of soft tissues. Stems, leaves, and other vegetable matter can be preserved through the carbonization process, where such parts are flattened between the two layers of rock. The chemical removal of the component produces a carbon film on one layer of rock, while an effect of the same component occurs on the other layer of rock.
Fossils of both soft and hard parts, which are too small to be noticed by the naked eye, are known as microfossils. A few fossils are completely devoid of animal and plant parts but represent evidence of the activities of organisms. Such organisms’ traces, which are appropriately called “trace fossils,” include trails or tracks, borings, and preserved waste products.
The highest majority of the fossils can be preserved in a water environment because land remains are destroyed very easily. Anaerobic conditions, which are at the bottom of the seas or other water bodies, are especially more favourable for preserving fine details since none of the bottom faunas, except for anaerobic bacteria, are available to destroy the remains. Generally, for an organism, which is to be preserved, two conditions should be met: possession of the hard parts, which are capable of being fossilized; rapid burial to retard decomposition and also to prevent the ravaging of scavengers.
In some of the places, such as the Grand Canyon - Northern Arizona, we can notice a great thickness of approximately horizontal strata representing the sediment deposition on the seafloor over several hundreds of millions of years. Often, it is apparent that every layer in such a sequence has fossils, which are distinct from the layers which are below and above it. In such layer sequences in various geographic locations, either or similar or the same, faunas or fossil floras take place in the identical order. By comparing such overlapping sequences, it can be possible to build up a continuous record of floras and faunas that have progressively more in common with the present-day life forms, same as the sequence’s top is approached.
Study of Fossil
The study of the fossil record has provided more required information for at least four various purposes. The progressive changes, which are noticed within an animal group, can be used to define the evolution of that group. Also, fossils provide the geologist with an easy and quick way of assigning a strata’s relative age, where they take place. The precision with which this can be done in any specific case is based on the abundance and nature of the fauna: a few fossil groups were deposited during longer time intervals compared to others. Fossils, which are used to identify the geologic relationships, are called index fossils.
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Fossil organisms can provide more information about the environment and climate of the site where they were preserved and deposited (for example, certain species of the coral require shallow water, warm, or certain forms of deciduous angiosperms may grow only in colder climatic conditions).
FAQs on Fossil
1. What is a fossil and how is it formed?
A fossil is the preserved remnant, impression, or trace of a plant or animal from a past geological age. For an organism to become a fossil, it typically needs to have hard parts like bones or shells and be buried rapidly after death. This rapid burial in sediment (like sand, silt, or mud) protects it from decomposition and scavengers. Over millions of years, as layers of sediment build up, the remains can undergo processes like permineralization, where minerals seep into and harden the organic material, turning it into stone.
2. What are the different types of fossils scientists study?
Scientists study several types of fossils, each providing different information about past life. The main types include:
- Body Fossils: These are the preserved remains of an organism's body, such as bones, teeth, or shells. They can be unaltered or petrified (turned to stone).
- Moulds and Casts: A mould is an impression of an organism left in the rock after the original remains have dissolved. If this mould is later filled with other minerals, it forms a cast, which is a three-dimensional replica of the original organism.
- Trace Fossils: These are not remains of the organism itself but evidence of its activities. Examples include fossilised footprints, burrows, and waste products (coprolites).
- Carbon Films: When an organism decays, it can leave behind a thin film of carbon residue, preserving a detailed silhouette, which is common for plants and insects.
3. What is the importance of studying fossils in science?
The study of fossils is crucial for several scientific disciplines. Firstly, fossils provide the most direct evidence for evolution, showing how life forms have changed over millions of years. Secondly, they help geologists determine the relative age of rock layers; specific fossils, known as index fossils, are used to correlate rock strata from different locations. Lastly, fossils offer valuable clues about past environments (palaeoenvironments), such as the climate and geography of an area when the organism was alive.
4. Why are most fossils found in sedimentary rocks and not in other types?
Most fossils are found in sedimentary rocks because of the way these rocks are formed. Sedimentary rocks are created from the gradual accumulation of sand, mud, and silt, often at the bottom of lakes, seas, or oceans. This process allows dead organisms to be buried gently and quickly, which is essential for preservation. In contrast, igneous rocks are formed from molten magma, and the intense heat would destroy any organic remains. Metamorphic rocks are formed under extreme heat and pressure, which would distort or obliterate any fossils contained within the original rock.
5. How do scientists determine the age of a fossil?
Scientists use two primary methods to determine the age of fossils. The first is relative dating, which determines if a fossil is older or younger than another. This is done by observing the position of the fossil in layers of sedimentary rock (strata); fossils in lower layers are generally older than those in upper layers. The second method is absolute dating, which provides a more precise age in years. The most common form of this is radiometric dating, which measures the decay of radioactive isotopes, such as Carbon-14 or Potassium-Argon, within the fossil or the surrounding rock.
6. Why is the fossil record considered incomplete?
The fossil record is considered incomplete because fossilisation is a very rare event. Most organisms do not become fossils for several reasons. Firstly, many organisms are soft-bodied and decay completely before they can be preserved. Secondly, the organism must be buried rapidly in the right kind of sediment to prevent decomposition. Finally, the fossil must survive millions of years of geological processes like erosion and metamorphism. Due to these specific conditions, only a tiny fraction of all organisms that have ever lived are preserved as fossils.
7. What is the difference between a mould fossil and a cast fossil?
A mould and a cast are two types of fossils that are often formed together. A mould fossil is a hollow impression or cavity left in the sediment after the hard parts of an organism (like a shell) have dissolved away. It's essentially a negative image of the organism. A cast fossil is formed when this empty mould is later filled with minerals or sediment that hardens over time, creating a solid, three-dimensional replica of the original organism's external shape.
8. Who are palaeontologists and what is their role in studying fossils?
Palaeontologists are scientists who study the history of life on Earth through the fossil record. Their role involves the careful excavation of fossils from rock, which requires meticulous documentation of the specimen's location and parts. They then clean, study, and analyse these fossils to understand the anatomy, behaviour, and evolution of ancient organisms, and to reconstruct the ecosystems of the past.
