Introduction
Basically, the word fossil is derived from the Latin word “Fossilis” which means ‘dug-up’. Form many years any curious and intriguing object that was dug out of the ground was considered to be fossils.
Modern definition
The dead preserved remains or relics or traces of any once-living form that liver prior to Recent times. In geological time scale, the Recent times means the period began about 10 to 15 thousand years ago. Thus, this term has been reserved for indicating prehistoric organisms.
Paleontology
The branch of science which deals with the study of the dead preserved relics and remains of plants and animals found in the crust of the Earth or simply put; the study of fossils is called paleontology.
Paleontology is from the Greek words
Palios = ancient, onta = existing, logos = knowledge
Paleontology is divided into the following categories:
- Paleobotany: The study of the fossils of plants is called paleobotany.
- Paleozoology: The study of the fossils of animals is called paleozoology.
- Invertebrate paleontology: The study of fossils of animals without backbone.
- Vertebrate paleontology: The study of fossils of animals with backbone or vertebral column.
- Palynology: The study of fossils of spores or pollens is called palynology.
- Micropaleontology: The study of fossils that are so tiny and minute that they can not be seen with the naked eye and are studied under a microscope only.
Conditions for Fossilization
The organisms that lived during the geological past, only tiny fraction of them have been preserved. According to an estimate, one only out of each thousand species of prehistoric organisms have been fossilized. It is due to the fact that normally the remains of dead plants and animals are totally destroyed.
Which conditions are required for their preservation? The answer to this question is that there are three special conditions that appear to be vital for fossilization. These are:
- 1)Possession of hard parts,
- 2) Escape from immediate destruction and
- 3) Rapid burial is suitable medium.
1. Possession of Hard Parts
Plants and animals have a much better chance of being preserved as part of the fossil record if they have hard parts. These hard parts typically include teeth, bones, shells, in animals also chitin. And in plants, it may be chitin or the woody tissues of plants.
Under exceptionally favorable conditions, however, even soft and delicate organisms such as jellyfish, worms, and insects may be preserved as impressions or carbon residues.
2. Escape from Immediate Destruction
Usually, when an organism dies, its soft parts are quickly eaten by scavengers and decomposed by bacteria or fungi. Again, the remains of these organisms are destroyed by the work of the atmosphere and other mechanical forces like rain, temperature, heat, pressure, strong winds, wave action, and crushing.
Rapid burial is therefore important condition favoring preservation and fossilization.
3. Rapid burial in a Suitable Medium
The type of protective material in which an organism is buried usually depends on the environment in which that organism was living.
- Marine Animals
Marine animals are more likely to be preserved because decay is controlled by saltwater. There are many animals that secrete shells and fish which have bony skeletons that live in oceans.
When these animals die, their hard parts are set to the bottom of oceans and are covered by soft sediments and thus prevented from scavengers and oxidation. Later, they remain buried in the rock that forms sediment, and thus, they are preserved as fossils.
- Land Animals
Organisms which live on land are less likely to be fossilized compared to marine organisms. The dead remains of terrestrial organisms are found in lakes, windblown deposits, or swamps. Animals living in deserts may be preserved by desiccation.
Such remains are called natural mummies. Many extinct spiders and insects have been found encased in amber – the hardened resin of ancient trees.
- Volcanic ash or Lava
In rare instances, lava, volcanic ash, or dust may also play the role of protective medium in fossilization. The bones and teeth of an early rhinoceros have been found in basalt and the remains of many plants have been preserved after being buried by lava and falling ash.
The protective material producing the most remarkable preservation is ice or frozen soil. Animals living in eras of glacial cold were frozen into ice. Their remains are found in such a remarkable state of preservation that even the flesh, hair, and stomach contents have been perfectly preserved.