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| A fossil is the representation of ancient life. What remains after a plant, animal, or insect dies might be the original remains like teeth, bone, shell, or plant tissue. In other cases over long periods of time, the original material may be chemically replaced and we see the structure of what once was. In still other instances we may only see traces of an organisms activity like tracks or burrows. Generally speaking, fossils only occur in sedimentary rocks or in rocks that were originally sedimentary in nature. Scientists who specialize in the study of fossils are known as paleontologists and the term paleontology refers to this study. | The difficult task of reconstructing the ancient life is done through the use of fossils by scientists in the various earth sciences, including paleontology and geology (a broad term meaning the study of the planet earth). Paleontology is often confused with archeology or anthropology. Anthropologists and archaeologists study what ancient remains can be found of human culture and paleontologists study the ancient life on earth that existed from about 3.6 billion years ago (Archean Period of the Precambrian Era) to approximately 10,000 years ago (Holocene Epoch). |
| Fossils provide more for us than one might think. Firstly, by combining the sciences of geology and biology we can correlate and date various formations of sedimentary rocks. Fossils aid the petroleum geologists in their search for oil. Fossils encourage us to think about the diversification of life. Fossils can either be very simple or extremely complex like ourselves. Biologists use this characteristic to aid in the classification of living species and to study the evolution of anatomical and physiological features. At various times throughout the history of the planet earth, extinctions have occurred which are “locked into” the fossil record. | Scientists study this in order to try to understand why this happened so that we may possibly avoid a similar demise. Studies of plate tectonics and evolution would not be possible without fossils. Astronomy, ecology, geology, biology, and evolution all rely on fossils. They are important teaching tools for all of these sciences. Finally, fossils are to many people, objects of beauty and curiosity. Fossils can be considered natures mysterious art. |
| Burrows, tracks, trails and other marks left by an organism’s activity are known as trace fossils. Because they are the direct result of activity, scientists use trace fossils to reveal behavior of extinct animals. Sometimes, however, the animal that made the particular kind of trace cannot always be distinguished. | Many times, this is the only type of fossil that is preserved. Examples of these include coprolites (fossilized excrement), dinosaur trackways, and groups of nests. From these, paleontologists speculate about feeding habits, body size, means of locomotion, and social behavior. |
| After years of studying fossils, scientists have found that it is fairly common for species to appear almost suddenly, remain unchanged for millions of years, and then completely disappear. The Cambrian Era represents this point in that at least 25% of the phyla that existed are now extinct. Diversity of the phyla has since increased from that time, but no new phyla have arisen. Fossils indicate that throughout geologic time mass extinctions have occurred. | What caused these extinctions is not clear, but it can be assumed that contributing factors might be environmental catastrophes, overpopulation, or simply survival of the fittest (species more adaptable to their environment forcing out other species). It is apparent that after a period of extinction there is a new diversification within existing phyla. |
| Because of people’s desire to understand the world in which they live, it has become common practice to name and classify things that they see. In order to understand the way in which organisms differ or are related, classification schemes use a hierarchical approach. Traditionally there are five kingdoms for living organisms: Animalia, Fungi, Monera, Plantae and Protista. | The kingdoms are then divided into phyla, which are subdivided into classes, orders, families, genera and finally, species. Similarities of organisms yield the belief that they are derived from common ancestry and are therefore classified within a similar hierarchical division. It is thought that through classification we can better understand relationships and complexities of organisms. |
| When a living thing dies it is most often decomposed completely by bacteria and other living things. Only under certain circumstances will any parts or traces of an organism be preserved or “fossilized.” In order for this fossilization to occur it is essential that the organism be buried rapidly. | This rapid burial provides a sealing effect from bacteria and oxygen that would have completely destroyed the organism. Except in extremely rare conditions, soft parts are never fossilized. It is more common to find fossilized hard skeletal remains or trace fossils. |
| Currently there are several processes of fossilization that we recognize. Fossils that have been buried for very long periods of time may undergo two or more processes. Pseudomorphisis is a process in which the original material fills with minerals resulting in a cast of the organism with no internal structure or organic material preserved. Distillation preserves organisms as carbon films after certain chemicals dissipate and are then represented as residual organic material. Dissolution processes occur within the rock and leave a mold of the original organism, or a trace fossil. Permineralization is a process in which wood and bones are preserved in their original state but the cellular structure is filled with minerals. Replacement often occurs after the cell spaces have been filled through permineralization. | Replacement causes the original cell walls to dissolve, leaving visible structure but frequently destroying all organic material. Interment is the process of preservation where an organism is covered by mud, sand or volcanic ash. Recrystallization occurs in some mollusk and echinoderm exoskeletons when there is a crystal structure modification. Refrigeration processes occur when plants or animals are frozen in permafrost. Dessication results when organic material is found in conditions void of moisture such as dry caves - dehydration results and material can be preserved for thousands of years. |
| The planet earth is truly a dynamic place. Processes of weathering or erosion are continually taking place, breaking down rock, transporting it to lower lying areas and ultimately becoming rock once again. Mountains are built, providing material for the building of more rock layers. The passage of time is recorded in this sedimentary rock. By studying the layers of sedimentary rocks and the fossils they contain, it is evident that patterns exist and can be correlated world-wide. | These patterns have helped us to construct a Geologic Time Scale that is divided on the basis of organisms’ appearance and extinctions. Radioactive isotopes found in sedimentary rocks containing fossils allow scientists to date the rock, and subsequently, the fossil by utilizing known physical decay rates of the isotopes. |
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