both comparative anatomy and paleontology.
The next great breakthrough in paleontology came not through the result of fossil analysis but by way of the studies of existing species. With their theory of natural selection, Darwin and Wallace, who developed it at roughly the same time in the mid-nineteenth century, offered an explanation for extinction that connected geological and climatic change with species transformation. Changes in the environment forced life forms to adapt; those that did so effectively survived, passing on their characteristics to new generations, while those that did not died out. p> New theories from outside the discipline have also contributed to paleontology in the twentieth century. Of these the two most important are the geological theory of continental drift, which explains how the major landforms on Earth have shifted over time, offering a new understanding for the distribution of various species, existing and extinct. The asteroid theory of extinction, also from the late twentieth century, has offered a powerful causal factor for the various extinction events in Earth's history, though some paleontologists still believe that mass volcanic activity, either independent of asteroid collisions or connected to them, are the major cause of such events. In either case, it is these catastrophic events that mark a number of key divisions between eras and periods. p> From within the discipline, perhaps the most important theoretical development of the late twentieth century has been that of punctuated equilibrium. First propounded by American paleontologists Niles Eldredge and Stephen Jay Gould in the 1970s, this theory revisits-in biology rather than geology - the old uniformitarianism-catastrophism debate of the eighteenth century. What Eldredge and Gould argue is that evolution, even in the absence of non-catastrophic events, is marked by bursts of genetic change followed by long periods of stasis.
Twentieth century technology has also given paleontologists remarkable new tools. Radiometry has allowed for precise and accurate dating of fossils while DNA analysis has opened a window on changes at the molecular level, permitting paleontologists to study precisely how species have evolved or failed to evolve. DNA analysis has also given scientists the ability to map the relationships, based on subtle changes in fossilized DNA, between species with incredible precision. p> While paleontology is largely seen as an interesting academic exercise by much of the public, as well as a source of fascinating facts for dinosaur-loving children, it may also offer lessons about humanity's current relationship to its environment. The current period in paleontological history, known as the Quaternary, which began roughly 1.8 million years ago, has been marked by the rise to dominance of a species from the hominid family of the primate order of mammals, known as homo sapiens. With its great intelligence this species has come to control and change its environment to an unprecedented degree and, in paleontological terms, in a very short period of time. Like the cataclysmic events of the past, human-wrought change to the environment may be occurring too fast for other species to adapt. Scholars of the environment estimate that species extinctions in the past century have occurred at a rate anywhere between 100 to 1,000 times above the average, or "background," rate of extinction - a result of hunting, pollution, habitat loss and, most recently, climate change. Thus, some paleontologists hypothesize that the planet may be undergoing a new extinction event, known as Holocene extinction event, after the current epoch, which began about 10,000 years ago, produced not by asteroids or great geological forces but by the very species that had unraveled the story of Earth's long history. br/>
REFERENCES
1. L. Sprague and Catherine Crook de Camp. The Day of the Dinosaur. New York: Bonanza Books, 1985. p> 2. Edwards, Wilfrid Norman. The Early History of Paleontology. London: British Museum of Natural History, 1967. p> 3. Gould, Stephen Jay. Dinosaur in a Haystack: Reflections in Natural History. New York: Harmony Books, 1995. p> 4. Rudwick, Martin J.S. The Meaning of Fossils: Episodes in the History of Palaeontology. Chicago: University of Chicago Press, 1985. br/>
