Changes

Determining absolute ages through physical or chemical techniques such as radioisotope analysis, magnetostratigraphy, or fission-track dating is not, by itself, a paleontologic application. Approximate absolute ages can be derived for [[fossil assemblage]]s in strata; a number of time scales have been published relating absolute age to the established sequence of (primarily planktonic) fossil events. Three of the most commonly used scales are Berggren et al.,<ref name=ch17r12>Berggren, W. A., D. V. Kent, and J. J. Flynn, 1985a, Paleogene geochronology and chronostratigraphy, in N. J. Snelling, ed., The Chronology of the Geological Record: Geological Society of London Memoir 10, p. 141–195.</ref><ref name=ch17r13>Berggren, W. A., D. V. Kent, and J. A. van Couvering, 1985b, Neogene geochronology and chronostratigraphy, in N. J. Snelling, ed., The Chronology of the Geological Record: Geological Society of London Memoir 10, p. 211–260.</ref><ref name=ch17r14>Berggren, W. A., D. V. Kent, J. D. Obradovich, and C. Swisher, 1992, Towards a revised Paleogene geochronology, in D. R. Prothero, W. A. Berggren, eds., Eocene-Oligocene Climatic and Biotic Evolution: Princeton, Princeton University Press, p. 29–45.</ref><ref name=ch17r15 /> Haq et al.,<ref name=ch17r43>Haq, B., U., J. Hardenbol, and P. R. Vail, 1988, Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change, in C. K. Wilgus, B. S. Hastings, C. G. St. C. Kendall, H. W.  Posamentier, C. A. Ross, and J. C. Van Wagoner, eds., Sea-level Change: An Integrated Approach: SEPM Special Publication 42, p. 71–108.</ref> and Harland et al.<ref name=ch17r44>Harland, W. B., R. L. Armstrong, A. V. Cox, L. E. Craig, A. G. Smith, and D. G. Smith, 1990, A Geologic Time Scale—Revised Edition: Cambridge, Cambridge University Press, 263 p.</ref>

Determining absolute ages through physical or chemical techniques such as radioisotope analysis, magnetostratigraphy, or fission-track dating is not, by itself, a paleontologic application. Approximate absolute ages can be derived for [[fossil assemblage]]s in strata; a number of time scales have been published relating absolute age to the established sequence of (primarily planktonic) fossil events. Three of the most commonly used scales are Berggren et al.,<ref name=ch17r12>Berggren, W. A., D. V. Kent, and J. J. Flynn, 1985a, Paleogene geochronology and chronostratigraphy, in N. J. Snelling, ed., The Chronology of the Geological Record: Geological Society of London Memoir 10, p. 141–195.</ref><ref name=ch17r13>Berggren, W. A., D. V. Kent, and J. A. van Couvering, 1985b, Neogene geochronology and chronostratigraphy, in N. J. Snelling, ed., The Chronology of the Geological Record: Geological Society of London Memoir 10, p. 211–260.</ref><ref name=ch17r14>Berggren, W. A., D. V. Kent, J. D. Obradovich, and C. Swisher, 1992, Towards a revised Paleogene geochronology, in D. R. Prothero, W. A. Berggren, eds., Eocene-Oligocene Climatic and Biotic Evolution: Princeton, Princeton University Press, p. 29–45.</ref><ref name=ch17r15 /> Haq et al.,<ref name=ch17r43>Haq, B., U., J. Hardenbol, and P. R. Vail, 1988, Mesozoic and Cenozoic chronostratigraphy and cycles of sea-level change, in C. K. Wilgus, B. S. Hastings, C. G. St. C. Kendall, H. W.  Posamentier, C. A. Ross, and J. C. Van Wagoner, eds., Sea-level Change: An Integrated Approach: SEPM Special Publication 42, p. 71–108.</ref> and Harland et al.<ref name=ch17r44>Harland, W. B., R. L. Armstrong, A. V. Cox, L. E. Craig, A. G. Smith, and D. G. Smith, 1990, A Geologic Time Scale—Revised Edition: Cambridge, Cambridge University Press, 263 p.</ref>

Time scales are revised and updated in the literature as new data become available.<ref name=ch17r15 /><ref name=ch17r42>Gradstein, F., M., Agterberg, F., P., Ogg, J., G., Hardenbol, J., Van Veen, P., Thierry, J., Huang, Z., 1995, A Triassic, Jurassic, and Cretaceous time scale, in Berggren, W., A., Kent, D., V., Aubry, M.-P., Hardenbol, J., eds., Geochronology, Time Scales, and Global Stratigraphic Correlation: Society for Sedimentary Geology (SEPM) Special Publication 54, p. 93–125.</ref> These time scales differ somewhat in the absolute ages assigned to the various fossil events (inceptions and extinctions). In most applications, the consistent use of a single time scale is more important than the choice of scale. Although absolute ages are not necessarily critical for well correlations, they are vital in studies that rely on determinations of geologic rates.

Time scales are revised and updated in the literature as new data become available.<ref name=ch17r15 /><ref name=ch17r42>Gradstein, F. M., F. P. Agterberg, J. G. Ogg, J. Hardenbol, P. Van Even, J. Thierry, and Z. Huang, 1995, A Triassic, Jurassic, and Cretaceous time scale, in W. A. Berggren, D. V. Kent, M.-P. Aubry, and J. Hardenbol, eds., Geochronology, Time Scales, and Global Stratigraphic Correlation: Society for Sedimentary Geology (SEPM) Special Publication 54, p. 93–125.</ref> These time scales differ somewhat in the absolute ages assigned to the various fossil events (inceptions and extinctions). In most applications, the consistent use of a single time scale is more important than the choice of scale. Although absolute ages are not necessarily critical for well correlations, they are vital in studies that rely on determinations of geologic rates.

==See also==

==See also==