Author: Darcy Ross
Institution: University of Illinois Urbana - Champaign
Date: September 2010
Despite paleontology's inherent fixation on the dead-and-gone, the field is anything but sleeping. Since its inception, paleontology has been rife with fierce debate, fueled by powerful characters. Ideas we may now take for granted,extinction, evolution, plate tectonics, the age of the earth,were once so controversial that reputations were broken and great minds silenced to keep the ideas from blossoming. Technology was often a limiting factor for the acceptance of these concepts. For paleontology and its closely related "mother" field, geology, there is much to be found beyond what meets the naked eye. Trace radioactive elements, magnetism in small minerals, and even tiny fossils such as pollen grains weave a vivid tale far deeper than the mere presence of dinosaur or artiodactyl bones. When looking at the story of paleontology, it is best to start with its close associate, geology.
The Men Who Stare At Rocks
Between the 18th and 19th centuries, the industrial revolution spurred a flurry of interest in minerals and ores , primarily how best to acquire them. Geology therefore began to come into its own as a topic worthy of study. This led to discussion of the formation of the earth, though mostly in terms of the biblical great flood initially. There were those who began connecting the appearance of the rock layers and rocks formed to observable natural activities: namely, volcanic activity and sedimentation. With less than 6,000 years to work with, as was the age of the earth according to the archbishop James Ussher, it was difficult for geologists to explain the formations they saw with the natural processes of which they were aware.
Figure 1 The Geological Time Scale Credit: U.S. Geological Survey Department of the Interior/USGS http:// geomaps.wr.usgs.gov/
William Smith, the "father of stratigraphy" working as a canal surveyor in the early 1800's, noted that rock layers occurred in predictable sequences all across England. He began taking notes of the layers, or strata, everywhere he went and confirmed this trend. It was further realized that the fossils found within the rocks could be used to define the strata, which could be recognized not only locally but also globally. The results of his research brought new excitement to geology, and a rapid period of strata-naming began. These names would later become well-known as periods of geological time.
At this point, however, there was no effective way to relate time in years with the varying levels of rock,it was at best a record of a sequence of events with only a sense of relative time.
Lyell and Darwin: The Battle for Evolution
When Charles Darwin published "On the Origin of Species" in 1859, it was in direct opposition with the self-appointed guru of geology, Charles Lyell. When Darwin first boarded the HMS Beagle, he carried with him the 1830 textbook Principles of Geology recently published by Lyell. Although largely considered THE founding textbook of geology, it carried with it some ideas quite strange to us of the post-Darwin world. Lyell held the belief that species never truly die; should their natural climate return, the flora and fauna exhibited by the fossil record could easily come back into existence. As he stated in the textbook, Volume 1: "The huge iguanadon might reappear in the woods, and the ichthyosaur in the sea, while the pterodactyle might flit again through the umbrageous groves of tree-ferns." Lyell eventually relented on this issue and accepted some degree of extinction.
Darwin's theory of natural selection took time to gain acceptance, but even Lyell accepted the theory of evolution before his death. With this in mind, paleontologists began the hunt for transitional fossils. Early findings unveiled the link between reptiles and birds and the evolution of horses. Paleontology was advanced by an explosion of interest in bone collecting, exemplified in the famous "Bone Wars" of the late 1800's, where two influential paleontologists, Cope and Marsh, competed for years to discover more species, primarily dinosaurs, than one another. They resorted to some very shady tactics - bribery, shoddy techniques, and attempts to cut off each other's fundings.
Isotopes Revolutionized
Despite the growing collections, analysis technology lagged behind. In the early days, paleontologists were only working off of the general shape of the bones and their relative position in the stratigraphic record (and, therefore, time period). The morphometric (measurements of the shape of the bone) analysis had to wait until computers to significantly advance, but some interesting new scientific advances allowed geologists to better understand the stratigraphic column and the time it represented. Previously, estimates of the ages of the strata were made based on observed geological processes, namely erosion and sedimentation. Better understanding of radioactivity led to the new technique of radiometric dating.
Atoms exist in different isotopic forms. For example, the biologically-important atom carbon, which dominates all life forms, typically exists in two forms. There is a "heavy" form containing 6 protons and 8 neutrons (C14) and the much more prominent form that contains 6 protons and 6 neutrons (C12). C14 is formed when nitrogen is hit by cosmic rays in the upper atmosphere. This carbon isotope is slowly incorporated into plant products through photosynthesis and proceeds up the food chain. C14 is unstable, and decays into C12 at a known rate defined by its half-life, the amount of time it takes for 50% of a given amount of C14 to decay into C12. This is very useful for dating "recently" dead organisms, extending as far back as 50,000 years.
Linking the Present to the Past
Isotopes can be used for more than mere dating. Oxygen isotope analysis has revealed tremendous amounts about the climate of the earth over time. Scientists can compare the ratios of normal oxygen (O16) and heavy oxygen (O18) to gather data about rainfall and global temperatures. Samples can be taken from ice cores on mountaintops and the earth's poles or fossilized shells of marine animals and plants. Corals and shells are often composed of calcium carbonate (CaCO3) or silicon dioxide (SiO2), and therefore incorporate the different isotopes at a rate proportional to the amount available in the ocean. While it can be a useful technique, scientists must account for many other factors that affect the uptake of oxygen in the shells. Carbon and nitrogen isotopic ratios can tell us about the diets of animals in several different ways. For instance, the normal carbon-12 to carbon-13 ratio can reveal whether the animal ate more C3 plants or C4 plants (the terminology refers to two different mechanisms in photosynthesis).
Figure 2 Plankton Bloom Near Hokkaido, Japan Credit: NASA image by Norman Kuring MODIS Ocean Color Team http://earthobservatory.nasa.gov/IOTD/view.php?id=38917
In the July 28, 2010 edition of the journal Nature, American and Canadian scientists reported their findings on ocean biodiversity as related to factors such as ocean temperature, latitude, and proximity to human activity. Among many significant trends that lay beyond the scope of this paper, they found that warmer areas of the ocean tended to sustain a high level of biodiversity. This proves to be a disturbing finding when combined with the news that phytoplankton species are on the decline due to ocean warming. Phytoplankton are microscopic photosynthesizing organisms that make up the lowest level of the food chain for aquatic life. They are significant producers of oxygen and actively reduce the levels of carbon dioxide. The ocean has phytoplankton blooms that can be seen from space.
During El Niño periods, the decline in phytoplankton results in the death of many ocean creatures and the birds that feed on them. As the Earth experiences more continuous global warming, such food chain upsets will become more frequent and widespread. Isotope relationships are now being used to better unravel the complex ocean food chains, which can help conservationists pinpoint their efforts to protect the areas that will threaten ocean (and, subsequently, worldwide) biodiversity. El-Sabaawi and his collaborators used carbon and nitrogen isotopes, in conjunction with fatty acids, to show the location of several marine organisms on the food chain. This could be applied across threatened ecosystems or even to pivotal ecosystems before they become endangered.
Isotopic relationships are still being discovered, but even what we've learned in the past 50 years is helping us understand the past and predict how events may unfold in the future, particularly regarding climate change. Isotopes and precise methods of dating can unravel sequence of events during these climate changes. For instance, professors David Fox and Paul Koch at the University of California detailed the relationship between increasing C4 plant life and the ungulates (deer, cattle, goats) of the Great Plains area of the US. With this sort of precision into our past, we can see how global warming will affect regional areas and the flora and fauna within that environment. Knowing details about such changes can help us prepare for damage control and to know which organisms will be hit hardest and soonest. In the battle for maintaining biodiversity, this is most certainly a matter of life and death.
References
"Bone Wars: The Cope-Marsh Rivalry." Accessed July 2010.
El-Sabaawi, R.W.; Sastri, A.R.; Dower, J.F.; Mazumder, A. 2010. Deciphering the Seasonal Cycle of Copepod Trophic Dynamics in the Strait of Georgia, Canada, Using Stable Isotopes and Fatty Acids. Estuaries and Coasts. Vol 33, Number 3, pp 738-752. DOI: 10.1007/s12237-009-9263-8
Fox, David L.; Koch, Paul L. 2003. Tertiary history of C4 biomass in the Great Plains, USA. Geology v. 31, no. 9, pp 809-812.
Lyell, Charles. 1830. Principles of Geology. Volume 1.
"Paleoclimatology: the Oxygen Balance." NASA's Earth Observatory. Accessed July 2010.
Tittensor, D.P.; Mora, C.; Jetz, W.; Lotze, H.K.; Ricard, D.; Vanden Berghe, E.; Worm, B. 2010. Global patterns and predictors of marine biodiversity across taxa. Nature. DOI: 10.1038/nature09329
Trefil, James S. 2003. The Nature of Science. Houghton Mifflin Harcourt. pp 343-344.
Author: Darcy Ross
Reviewed by: Phuongmai Truong, Renee Gilberti, and Yangguang Ou