Paleontology

Summary

Paleontology is an interdisciplinary field concerned with the study of the record of life through time and the application of that information to solve scientific problems. Fossils are particularly used in the relative dating of rocks, which is important information for the mineral and petroleum industries. However, paleontology also provides valuable data to understand past life and, therefore, an understanding of extinction events and the effects of climate change. Modern technology is increasingly used to help solve problems, including computed tomography (CT) scanning to reconstruct the anatomy of extinct organisms.

Definition and Basic Principles

Paleontology is the study of fossils, or once-living organisms, preserved within sediment. The term "paleontology" is derived from the Greek palaios for "ancient," ontos for "being," and logos, for "study." Therefore, paleontology does not encompass the allied field of archaeology and overlaps only slightly with anthropology, both of which focus on humans. Traditionally, the study of fossils has been aimed at reconstructing the organisms and analyzing them to develop an understanding of their evolutionary relationships. This has been enhanced by the advent of cladistics, a computer-based analytical method that significantly increases the speed and rigor of such studies. In addition, the careful tabulation of fossils over several hundred years of study has enabled the development of a relative geological timescale that is the basic tool in all study of the crust of the Earth. Paleontology is an important industrial tool that helps extractive industries such as the petroleum and minerals industries understand where to find oil and minerals.

Increasingly, paleontology is viewed as a potentially valuable predictive tool. The results of earlier climate changes are preserved in the fossil record and may help scientists understand the effects of global warming or other future climate changes.

Background and History

Fossils were probably picked up and admired long before they were studied, but the ancient Greeks recognized that some of these objects represented marine organisms and could be used to determine where oceans had once been. In medieval times, fossils were often viewed as magical objects. For example, fossil shark teeth were termed glossopetrae, or "tongue stones," and were thought to provide protection from snakebite. They were viewed as structures that had "grown" within the rocks, rather than the remains of actual organisms. In the seventeenth century, Nicolaus Steno demonstrated that glossopetrae were shark teeth by dissecting a modern shark and showing the similarity of its teeth to the fossils. At about the same time, Robert Hooke used early microscope technology to show that fossils and modern wood and shells had the same internal structure.

Once fossils were accepted as representing past life, they could be studied as such. In some sequences, scientists found clear evidence of mass extinction events in which whole faunas were replaced over short periods of time. In the early nineteenth century, work by French naturalist Georges Cuvier in the Paris basin showed that numerous mammals that lived when those rocks were laid down no longer existed. Studies of this type showed that long periods of time had been necessary for the evolution and extinction of groups of fossil organisms. At about the same time, English canal surveyor William Smith determined that fossils could be used as time markers, representing the period they were present on the surface of the Earth, and the theory became known as stratigraphy. His findings were developed into the geological timescale, which is still being refined but provides a basis for dating rocks in a relative sense.

How It Works

Dating. Understanding the spatial relationships of rocks developed from the need to predict where materials of economic value could be found. Initially, distinct rock beds were used to correlate between places, but this method was imprecise over long distances or in areas where the rocks were folded and faulted. Rock units could not be dated effectively until Smith realized that the geological succession corresponded to a regular, nonrepeating succession of fossils. Fundamental to this process of biostratigraphy is the use of zone fossils that represent a period of time equal to the duration of the species before it became extinct and that are widespread enough to enable useful correlations to be made. Increasingly, microscopic fossils (such as the marine, planktonic, and unicellular foraminifera) are used as they have the advantage of being very abundant in sediments and having short time ranges, allowing for accurate dating.

Taphonomy. The quality of the fossil record must be understood for it to be useful in applications such as dating or understanding mass extinctions or biodiversity loss. Taphonomy, which is the study of the processes that affect organisms from death to burial in sediment, is integral to such an understanding as it allows an evaluation of the extent to which the fossil record mirrors the original faunal situation. Most organisms do not become fossils, and those that do will first undergo decay of the soft tissues, then transport and breakage of the hard tissues, and finally, their burial and modification. For example, soft-bodied organisms can make up 50 to 60 percent of the organisms in present-day marine settings, and in most cases, none of those organisms will be fossilized. Experimentation on modern forms shows that the presence of oxygen is vital to the initial breakdown of soft tissues, and its absence can lead to conditions of special preservation that result in unusually well-preserved faunas such as the Burgess Shale fauna (a Middle Cambrian age site in Canada). The breakage and disarticulation of organisms can be simulated in the laboratory or observed in nature. These studies show that organisms go through several stages as they progress toward fossilization. Factors that affect whether they are preserved include the presence of hard parts, how common the organisms are, and their life environment, as organisms living in areas of sedimentation (particularly aquatic environments) have a better chance of preservation. Processes within the rock, such as water filtering through, may result in the replacement of the fossil or its total removal. Of course, before the information contained in the fossils can be used, the fossils must be found by a paleontologist and studied.

Taxonomy and Phylogeny. An understanding of the relationships of organisms enables scientists to appreciate and evaluate extinction events and the effects of climatic change, as well as to use fossils in dating. Naturalist Charles Darwin's views on natural selection led to an understanding of the evolutionary processes that result in the development of new species and of phylogeny, the pattern of relationships of organisms, often shown as a branching diagram. Phylogeny has been greatly aided by the method termed cladistics, or phylogenetic analysis, developed by the German entomologist Willi Hennig in the mid-1900s. Hennig's method recognizes and orders characters in an objective fashion to show the most likely evolution of organisms through time. As it involves the processing of large amounts of data, this system lends itself well to the use of computer programs such as PAUP (Phylogenetic Analysis Using Parsimony). Results are presented as regularly branching diagrams, or cladograms, showing the relative sequence of speciation events.

Applications and Products

Geological Dating. The ability of geological industries to accurately locate the materials they seek depends largely on an understanding of the structure of the Earth's crust. It is initally important to realize that rocks are normally laid down horizontally and that they become younger toward the top of any sequence. Detailed understanding, however, requires the ability to relate rocks of the same time period to one another, and this was not possible until fossils were recognized as providing unique temporal markers. Once this was understood, the sequences of rocks that had been recognized in discrete outcrops could be related to one another. During the first half of the nineteenth century, most of the relative timescale was assembled, showing the age relationships of rocks and detailing the sequence of fossils that could be used. The oldest fossil-bearing rocks were described as from the Paleozoic (ancient life) Era, followed by Mesozoic (middle life) and Cenozoic (new life) Eras. Within these eras, the rocks were divided into periods, such as the Cambrian, Ordovician, and Silurian—part of the early Paleozoic Era—and the Cretaceous period, the last in the Mesozoic Era.

As the study of dating became more laboratory-based—and in response to the requirements of the oil industry, whose samples were typically drilling chips, which were too small to contain recognizable fossils—paleontologists moved toward using microfossils. These can be the remains of very small organisms or small parts of organisms as long as they are common and widespread and show evidence of having evolved rapidly.

The field of applied micropaleontology started in the late 1800s in Poland when paleontologist Józef Grzybowski described the foraminifera from the Carpathians in a series of monographs and then applied his findings to foraminifera from the Galician oil fields. He was soon able to demonstrate that it was possible to correlate subsurface strata in wells drilled for petroleum exploration using these fossils. The methods pioneered by Grzybowski continue to be used, and the study of microorganisms has been very much centered on the requirements of the petroleum industry.

Thermal Maturation. Organic microfossils such as spores and pollen can be used to indicate the temperature reached by the rocks (thermal maturity) that contain them because temperature increases as the rock is buried deeper. Organic microfossils are progressively altered by the loss of hydrogen and oxygen, and the resultant changes to physical properties such as color, reflectivity, and fluorescence can then be measured.

Reflectivity studies using vitrinite, an organic component, were initially carried out on coal to determine its rank, or thermal maturity. These studies were then applied to hydrocarbon generation, as hydrocarbons such as oil and gas are generated over time by the action of heat on fossil organic material. The reflectivity of vitrinite in the hydrocarbon source rocks reveals maturity and the likelihood of the presence of oil and gas in the sediments.

Spores and pollen change color from pale yellow to orange to dark brown as the temperature increases, and these changes can be used to show the level of organic maturity. A similar change is seen in conodonts, tiny jaw elements from primitive craniates that were abundant in the Paleozoic Era, and an eight-point scale has been developed detailing a color change from pale yellow through black to colorless or clear. Below 60 degrees Celsius, organic material in rock is converted to kerogens and bitumen. Rock generates and expels most of its oil at temperatures between 60 and 160 degrees Celsius, and above 160 degrees Celsius, natural gas is formed. It is important for industry to understand the temperature level the rock has reached, and the application of thermal indices based on color or reflectivity provides that information.

Environment and Climate Change. Organisms are intimately connected to environments and, therefore, can be used to deduce past environments. This is particularly true of plants, which, unlike marine organisms, are directly exposed to the atmosphere. The size of leaves is related to temperature as well as humidity and light levels; leaves decrease in size as the temperature or humidity drops. Similarly, the ratio of serrated leaf margins to smooth margins varies according to temperature, and a 3 percent change in this ratio is equivalent to a change of 1 degree Celsius in the mean annual temperature. In addition, the numbers of stomata (small openings on the surface through which plants lose oxygen and water and gain carbon dioxide) vary according to the carbon dioxide level. When carbon dioxide levels are high, plants need only a small number of stomata, but when the levels are low, plants will commonly have large numbers of stomata to enable them to get all the carbon dioxide they need. Because carbon dioxide is a greenhouse gas and traps radiation from the sun, the higher the atmospheric carbon dioxide levels, the higher the temperature. Therefore, a correlation can be made between high global temperatures and low numbers of stomata on fossil leaves. If this technique is applied to the end of the Triassic period extinction, the large drop in the number of stomata on leaves that occurred at this time indicates an increase in atmospheric carbon dioxide and a consequent increase in temperature. Calculations suggest that the temperature would have increased by 5 degrees Celsius globally and possibly up to 16 degrees Celsius locally. In the twenty-first century, carbon dioxide levels are rising because of the burning of fossil fuels, and these studies of carbon dioxide in past eras can provide information that will help scientists understand what changes in biodiversity are likely to occur because of higher carbon dioxide levels.

To obtain information about the temperature of ancient ocean waters, it is possible to use oxygen isotopes extracted from calcareous marine fossils. The ratios of oxygen 16 and oxygen 18 vary, with oxygen 18 increasing as the temperature decreases. Using isotope ratios from foraminifera from deep-sea sediments, it has been possible to show that over the last 100 million years, there has been a steady increase in the oxygen 18 level, indicating a decrease in ocean temperatures of up to 15 degrees Celsius over that period.

Evolution and Extinction. Studies on modern taxa have provided much information on how change in organisms takes place, but the fossil record is still the best evidence of evolution through time and also of its correlative periods of extinction. Both of these areas are of interest because of their relevance to the changes in biodiversity that are taking place in the twenty-first century. To detail changes through time, it is necessary to develop a database of information on taxa and their longevity. That database is constantly gaining new entries and, therefore, never complete; however, it has reached the point where information can be derived from it using statistical techniques aided by computers. Extinctions are always occurring, of course, but these studies show that when the level of extinction exceeds that of the development of new species by a significant amount, a mass extinction has taken place. Although numerous extinction events have been recorded, there are seven major ones. The first occurred in the Middle Vendian period about 650 million years ago, followed by events at the end of the Cambrian, Ordovician, Devonian, Permian, Triassic, and Cretaceous periods, of which the end-Permian event is by far the most severe. Analysis of extinction rates of shallow marine organisms at the family level by University of Chicago paleontologists David M. Raup and Jack Sepkoski showed a 26-million-year periodicity to extinction events through the Mesozoic and Ceonozoic Eras that were interpreted to indicate an extraterrestrial cause for the extinction events. Corroborative evidence is generally lacking for all but the Late Cretaceous event, however, leaving uncertainty as to the underlying cause of the periodicity.

Careers and Course Work

Paleontologists may be trained initially as biologists or as geologists, but in either case, a solid foundation of basic science courses is required. For jobs in the industry, a Master's degree or a Doctorate is required, and the field of study would normally have to be in some aspect of micropaleontology, as that is the area of interest to the petroleum industry. However, the field has seen volatility associated with the ebb and flow of demand from the petroleum industry, and some universities have eliminated or reduced the size of their training programs. For example, in the mid-1980s, more than thirty universities in North America had programs in stratigraphic palynology (the use of spores in dating), but by the late 1990s, only two universities had such programs. However, by the second decade of the twenty-first century, the number of palynology programs at American universities had increased somewhat. Partnerships between industry and university programs have been touted as the way to maintain a flow of adequately qualified paleontologists.

Paleontologists may also be employed by universities and museums or by the US Geological Survey (USGS). Again, advanced degrees are typically required. However, the number of university paleontologists in North America has been relatively static, meaning jobs may be hard to find. Even as earlier generations of paleontologists approach retirement age, the trend has been for these positions to be replaced by faculty in other geoscience fields, particularly environmental geology, which became the top geology degree program in the 1980s and 1990s. The US Geological Survey, too, has reduced the number of its paleontology staff since the 1990s. Although museums have consistently responded to the popular interest in dinosaurs, this has not resulted in a significant increase in jobs for paleontologists. As of 2020, the US Bureau of Labor Statistics did not list paleontologists separately in its Occupational Outlook Handbook. It categorized the field and similar occupations under the umbrella term geoscientists. According to the bureau, about 29,000 people were employed in the geosciences at a mean annual salary of $93,580.

Social Context and Future Prospects

Paleontology has long enjoyed popularity in the public imagination due to its association with dinosaurs. Indeed, the field often sees surges of interest when major dinosaur discoveries are announced or even when dinosaur-themed films are released. The perception of paleontologists conducting fieldwork and unearthing spectacular fossils continues to inspire many people, though such findings are, in fact, rare. Even as actual demand for paleontologists has declined, the profession retains an important place in modern science as people strive to learn more about the world and its past. Meanwhile, technological advances and refinements of systems such as cladistics keep paleontology moving forward.

Paleontology also continues to be important to the fossil fuel industry. Although there is a growing movement toward greater use of renewable resources, fossil fuels remain a vital component of overall energy use. Therefore, paleontologists will still be needed in future decades to provide some of the basic data required in exploration to find such fuels. However, the numbers of paleontologists needed are still likely to decline rather than to rise.

One area in which paleontology could well have an effect in the future is in environmental studies and the study of climate change. As more emphasis has been placed on the protection of natural resources, an understanding of past changes and an ability to monitor present-day changes using microorganisms has become increasingly important. Further, paleontologists use their knowlege of past climates and ecosystems to help research climate conservation strategies.

Bibliography

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Benton, Michael J., and David A. T. Harper. Introduction to Paleobiology and the Fossil Record. 2nd ed. Wiley-Blackwell, 2020.

Foote, Michael, and Arnold L. Miller. Principles of Paleontology. 3rd ed. Freeman, 2007.

Kiessling, Wolfgang, et al. "Improving the Relevance of Paleontology to Climate Change Policy." Proceedings of the National Academy of Sciences, vol. 120, no. 7, Feb. 2023, doi.org/10.1073/pnas.2201926119. Accessed 28 May 2024.

Lipps, Jere H. “What, if Anything, Is Micropaleontology?” Paleobiology 7.2 (1981): 167–199.

Prothero, Donald R. Bringing Fossils to Life: An Introduction to Paleobiology. 3rd ed. Columbia UP, 2013.