[Chemistry Class Notes] Fossil Pdf for Exam

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.

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.

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.

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).