Theories of fossilization
Impression
Answers
Fossils are very important to us. This article will help you learn about fossil and it's various types found in details. What are the importance of fossil in our life? What are the factors and how coal is formed in nature and why they are so precious to us along with their different mode of formation.
What is fossil?
Fossil is the remain of either a plant or an animal in its full or fragmented part which was preserved by natural process and are discovered later on. According to "Arnold" in 1947, fossils may be defined as "the relic of some former living things- plants or animals embedded in or dug out of the superficial deposits in past geological periods."
Types of fossils :-
There are six types of fossils, they are explained below :-
1. Mineralised fossil or Pertrifications : In this type, both the external form and the internal structure of the plant is preserved in original form. The examples are silicified wood, coal-balls etc. The coal-balls are of localised occurrence which are irregularly rounded concrete masses, commonly made up of calcite containing preserved fragments of coal forming plants. Each coal-balls contains calcium carbonate, magnesium carbonate and sometimes iron sulphate.
2. Compression Fossil : A great pressure under which fossilisation takes takes place makes all round or solid organs to become flat and for that reason, the fossils forms a carbonaceous film. The external form undergoes modification by vertical pressure of the sediments and is known as compression.
3. Cast of Incrustations : In this type, the external form of the plant is preserved . The plant loses carbonaceous substance and the internal tissues are decayed . Due to the removal of the plant tissues, a cavity is formed which becomes subsequently filled up with sand or mud and which finally becomes solidified to form stone and finally an exact cast of the plant material is formed.
4. Impression fossil : The leaves or any other organic part falling on a partly rigid clay forms an imprint on its surface which is known as impression. Finally, the impression of fossils occur on the original soft matrix.
5. Mummified fossil: Plants or plant fragments are compressed by means of vertical pressure caused against one another, are known as compaction or mummified plants.
6. Amber : Amber is the excretory resinous substance from the injured part of the plant like "Pinus succinifera" which is of great commercial value as it sometimes encloses beautiful fossils of flower and insects.
Importance of fossil :-
The importance of different fossil plants are as follows:-
1. Diatomaceous earth belonging to algae is formed of skeleton of billions of diatoms depositing on the beds of sea which are of great industrial importance.
2. Graphite is a fossil in some sense which is thought to be of organic and is used in making lead pencils.
3. Different types of algal lime stones are formed from minerals which are considered as fossils of earlier ages.
4. Even petroleum may be considered as fossil which are of algal origin because organisms are liable for its creation.
5. The calcareous bodies associated with extensive deposits of stone are considered to be formed due to precipitation of lime by masses of blue green algae of previous ages.
6. The mega-fossil and micro-fossil plants of different ages help in the study of stratigraphic limit and stratigraphic identification.
7. The study of fossils helps the changes in organic life through the ages during the course of evolution through different ages during the course of evolution through different periods and time scales.
8. The determination of age and correlation of strata can be done with the help of fossil.
9. Coal is nothing but a highly compressed fossil originated from originated from the first age of the world forests in the Palaeozoic era of Carboniferous period.
10. The antiquity of land plants can be traced from the fossil evidences and in their existences.
Factors of Fossilation :-
1. Rapidity of burial in stagnant water.
2. Low amount of available oxygen.
3. Rapidity infiltration by mineral substances.
4. Protection against high winds.
5. Prevention of auto catalytic or microbial decomposition.
Modes of Fossilation :-
1. Infiltration theory : Infiltration of mineral substance takes place at first which is then followed by precipitation due to interaction between soluble mineral salts present in the surrounding water and certain compounds released during partial disintegration of plant cell walls. In this process, free carbon is released which reduces the sulphides present in water.
2. Molecule by molecule theory : According to this theory, decomposed material molecules of the plant body simply replaced by the molecules of minerals substances like lime carbonate, iron pyrites or silica. This theory is not widely