What is a fossil and how are fossils formed?
Fossils are preserved remains or traces of animals, plants or other living beings in rocks, such as body molds or body parts, tracks and footprints.
|Fossils: from a preserved foot bone to a preserved dino dropping.|
The science that studies fossils is paleontology. Fossilization rarely occurs because the organic matter of living beings tends to be rapidly decomposed. Therefore, for an organism to be fossilized, the remains must be covered with sediment as soon as possible. There are different types of fossils and different processes of fossilization.
When did people start studying fossils?
Man has always observed and tried to interpret nature. From a very early age he found rocks in the form of shells, animal bones and plant leaves, i.e. fossils
Over many centuries these impressions have stimulated the imagination of the human being and have given rise to countless explanations. Some of these explanations were considered to be creations of evil or good spirits, being called "stone snakes", "magic stones", "thunderstones" and "frog stones".
In other interpretations, impressions were seen as the result of the action of sun or star radiations. There were also those who preferred to look at them as jokes of the mineral kingdom, which imitated forms of plants and animals existing in nature.
Still in the 17th century there was the theory that the impressions left on the rocks would be the result of a property inherent to the Earth, which would originate these marks as ornament of the occult regions of the globe, in the same way that flowers are the ornament of the surface. Even in the 19th century, a study by the Christian Church claimed that the Devil had placed those imprints on the rocks to deceive and embarrass humanity.
Although many theories have emerged over time to interpret the meaning of fossils, their scientific study only began about 300 years ago. Their true origin and nature was only established in the 17th century by a few naturalists, who managed to establish the relationship between shark teeth of the time and other similar but fossilized ones. A century earlier, the name "fossil" had appeared. It derived from the Latin word "fossil", which means "excavated", and was initially used to designate all kinds of minerals and metals extracted from the earth's crust.
How do the people who study fossils are called?
Scientists who play the role of fossil detectives are called "paleontologists" because the branch of Earth and Life Sciences that is dedicated to the study of fossils is called "Paleontology".
Paleontologists have found fossils all over the world at a spectacular rate - every seven weeks a new fossil is found. But it's not easy to find a fossil. So finding fossil remains of an animal or plant is an exciting experience. Marine cliffs, quarries and other exposed rocks are places of great interest for fossil discovery. Also the caves, as ancient shelters of men and animals, can provide valuable paleontological discoveries.
Where can fossils be found?
Most of the time, no matter how well known the geological characteristics of a site are, it is not possible to say with certainty whether there will be fossils there or not. However, certain factors may be indicators of their presence and it is these factors that paleontologists follow in their research. These hypotheses refer mainly to the type of rock most related to the preservation of fossils, i.e. sedimentary, and the age of the rock, which is determined by chemical analysis of its composition.
There is also another way of working on the matter - digging blindly until you are lucky enough to find something. Some fossils are found at random, in construction sites or mining areas, for example.
Despite the difficulty in finding fossils, paleontologists have already found microscopic blue algae fossils, the age of which has been estimated at almost 2000 million years. Recently, bacteria fossils have been discovered that are about 3000 million years old.
How are fossils researched?
When the scientist reaches a probable area of fossil formation, he begins by looking for evidence at the points where erosion has removed the soil from above the rocks, and then investigates the sedimentary strata. If he finds traces there, such as skeletons or fragments of fossilized bones, he removes the rock above them, so that he can photograph them and then remove them without damaging them. Only very rarely is a fully preserved remains ever found. In most cases, the skeletons are quite fragmented, and many pieces may be missing. It is necessary to identify the bones with numbers, in order to make it easier to reconstitute the animal afterwards. The result of these works can be seen in natural history museums, where they are usually displayed.
But even without having fossils of bones that allow the reconstitution of living beings, other types of traces can provide very interesting information. For each type there are appropriate study techniques, which allow different conclusions to be drawn. For example, in a set of footprints, scientists measure the distance between them to see the length and speed of the animal, and its depth to determine its weight. The type of conclusions drawn are different from those drawn from droppings (coprolites). They are crushed until they become a fine powder which, after analysis, can give information concerning, for example, the type of food the animal was feeding.
How important is paleontology?
Paleontology is the science that studies the organisms that have populated the earth over time and whose remains and activity marks are preserved in sediments. The study of organisms is of great importance for the understanding and study of the history of the earth. Thus, paleontology is of interest to biology because it allows one to study the evolution of living beings.
For the study of animals that once inhabited the planet, it is not only their fossils that are important but also the marks left by their activity, that is, the paths, footprints and tracks.
Types of fossilization
For fossilisation to take place, the organism must be quickly sheltered from erosion agents, which happens when one or more of its constituent parts are quickly covered by sediment. This process takes place in four stages:
- When the animals died they were deposited on the bottom of the sea being quickly covered by sediments;
- When they were incorporated in the sediments they underwent the same phenomena of diagenesis and metamorphism, fossilizing;
- The rocks where the fossils are incorporated undergo modifications that raise some strata;
- Fossils, due to erosion or other factors appear on the surface some millions of years later.
The types of fossilisation are:
The hard parts of the organisms disappear leaving their marks (impressions) on the rocks, that is, the organism is destroyed but the shape persists.
As it is known there are two main types of mold fossils, the external in which the shell is printed on the sediments being later removed, and the internal in which the sediments cover the shell which is later removed leaving only the template of the internal surface. There are also the counter-mold which is the mold of the external mold.
MummificationThe remains of the organisms are preserved in whole or in part, usually in materials such as amber, ice, fossil resin.
MineralizationThe hard parts of organisms such as bones, shells disappear and instead become minerals. They are transported in groundwater. Tree trunks are good examples of this type of fossilisation.