The Study of Paleontology
1. Introduction to Paleontology
The concept of historical or evolutionary science is about the skeletal remains of extinct animals and plants, and the research of those remains. This includes comparative anatomy, taxonomy (the study of classification), and the methods involved in reconstructing the life of the past. Unlike traditional history, evolutionary history is based upon a comparative and genealogical approach. The primary objective is to piece together the history of modern beings and reconstruct the chronology of all that has preceded them. It is based on three principles: the principle of uniformitarianism, which assumes that the same natural laws and processes that operate in the universe now have always operated in the universe in the past; the second law is the law of superposition, which states that in sedimentary rock layers, the bottom layer is the oldest and the top layer is the youngest; the final law is the law of faunal succession, which states that groups of animals have a chronological sequence, and that when a group becomes extinct, another one appears in a similar order. Understanding these laws can be useful in attempting to date the origin of Earth and the events which have occurred on it.
2. Fossil Formation and Preservation
Fossilization begins with the inorganic and organic remains of the organism becoming encased in sediment. The hard parts of the organism, such as bones and teeth, are often able to be dissolved and replaced by minerals, preserving the shape of the original encasing. It is generally accepted that the end product of this process is what is considered a “true” fossil. This process is known as permineralization or petrification and is what most people think of as fossilization. Minerals do not always have to fill in the shape of the organism; impression and replication fossils are another way in which organic remains can be preserved. The shape of the organism can be preserved as a negative or positive imprint and in some cases the organic material is lost and replaced by the mold of cast of the original material. In the case of replacement, the original material is dissolved and replaced by another mineral. This preserves the shape of the original material, but is not technically a cast. Finally, there is an undocumented process of mineralization which preserves the shape of the organism in the same way as permineralization, but for which the scientific literature on the specific chemical processes is lacking.
The process of fossil formation is a great deal more complicated than what is portrayed in either the scientific or popular literature. For paleontologists, what is preserved with the fossil is really only part of the story. The great majority of organisms that die never become part of the fossil record. In some cases, the soft parts of the organism are lost or destroyed prior to burial by scavengers and decomposition. In other cases, the organism’s living situation does not favor fossilization. To become a part of the record, organisms must be buried rapidly so that decomposition is halted. Most biotic and abiotic agents work to degrade the remains of an organism. When an organism does become buried, how long it lingers in the “fossilizable” state is largely a matter of chance. If the organic material is not mineralized rapidly, it will be lost to the fossil record.
3. Evolutionary History of Life on Earth
With a known order of events, the next step is to establish a relative scale of time. This has been done throughout the history of paleontology in a number of ways using a variety of methods. Prior to the modern theory of plate tectonics, geologists constructed a time scale based solely on the order of rocks. This was primarily done by the use of index fossils; fossils that are clearly defined, easily recognizable, abundant, found in a wide area, and existed for only a short span of geologic time. These fossils can now be used to date their respective rocks in which they are found. In the present day, the time scale has been more clearly defined with the knowledge of plate tectonics and the movement of the continents. This has allowed for a more accurate scale of time correlating geologic events to the organic events they affected.
To understand historical processes in the history of life on Earth, paleontologists have studied the order in which events unfolded. It is a well-understood concept in paleontology that the processes seen in the present also occurred in the past. The most basic example of this is the Law of Superposition. In the present, as sediment is deposited, it builds up in horizontal layers. The layer at the bottom will harden over time and trap anything within it. This is equivalent to what happens when a sedimentary rock forms. The layer at the bottom of the rock is the oldest, and the layers become younger as you move upwards. Whatever may be preserved, such as a rock, a footprint, or a bone, is trapped within the sediment and will be preserved in its layer of formation. If later erosional processes remove a layer of sediment, it is like taking a slice of the layer cake. Whatever is left is a sequence of what was there before. This is why anything found within a rock must be older than the rock itself.
4. Methods and Techniques in Paleontology
A large range of methods and techniques are used in paleontology and are presented here in approximate order of increasing time depth of the subject material being studied. The first set of techniques are field based and involve locating fossil localities and then collecting the fossils. A number of different techniques can be used to find fossils. Geology maps are often a very useful starting point in the search for a fossil locality and knowledge of the area’s geology can be very important. Geological maps will usually indicate the age of the rocks, and the type of rock which may contain fossils, so it is often possible to use this information to locate potential fossil localities. Remember that fossils can be found in most types of sedimentary rock so do not be too focused on looking for a specific rock type. Once a potential fossil locality has been located, a technique called prospecting can be used to try to find fossils. This is usually done by walking over the area and keeping a sharp lookout for any fossils, which may be eroding out of the rock. Prospecting can take a lot of time and hard work, particularly in areas with poor outcrop, however, it is often a rewarding method of finding fossils. Other methods which can be used to locate fossil localities include aerial photography and satellite imagery. Any information on the location of potential fossil localities should be recorded on a detailed locality map.
5. Applications and Significance of Paleontology
A wide variety of scientific tests can be conducted on fossils to provide information about the conditions of life, preservation, and the changes which have occurred since the death of the organism. These tests have scientific applicability to geology, biology, biophysics, and chemistry. Techniques used on recent insects in amber have been replicated with some fossil insects to test the effect of viscosity and temperature on the rate of inclusion of the insect in the medium. The results of these experiments might someday help in the recognition of taphonomic conditions leading to the preservation of exquisite fossil specimens. At a simpler level, the silt which choked the life from a Jurassic pond is known today by the organic and inorganic compounds which comprise the ancient mud. As a progressor from knowledge of fossil fuel formation processes, a petrological study could provide a detailed history of diagenetic changes in the sediment and their effects on various organisms.
One of the most fascinating aspects of the study of paleontology is the piecing together of past life history through the discoveries of plant and animal fossils. Some important knowledge about the relationships between angiosperms and insect fauna has come from paleobiological studies in amber. This is a good example of scientific application from paleontology. In a modern replication of a 100 million year old association, it was proved that the amber had the ability to fossilize. Subsequently, it was then possible to test the copal from East Africa to see if it was old enough to have preserved an ancient biological association. A knowledge of the insect inclusions in the East African copal could be used to predict what might be found in the amber, and ultimately in the underlying Precambrian rocks in an area which is of importance for medical and agricultural paleoecological assessments.
