BIOLOGY Volume 3 - A Guide to General Biology - 2004

26. EVOLUTION, OR THE HISTORY OF LIFE ON EARTH

26.1. Theories of the Origin of Life

26.1.3. Steady-State Theory

According to this theory, the Earth never originated, but has existed eternally; it has always been capable of sustaining life, undergoing little to no change. Species, too, have existed for all time.

Estimates of the Earth's age have varied widely, ranging from roughly 6,000 years, as calculated by Archbishop Ussher, to 5 billion years based on modern radiometric dating Methods. As dating techniques have improved (Appendix 4), estimates of the Earth's age have continually increased, allowing proponents of the steady-state theory to suggest that the Earth has existed forever. Dismissing the general significance of geochronology for establishing the precise age of the Earth, supporters of this view use it as a basis to assume that the Earth is eternal. Under this theory, species also never originated; they have always existed, and any given species has only two possible fates—either A change in population size or extinction.

Proponents of this theory do not accept that the presence or absence of certain fossils can indicate the time of origin or extinction of a particular species, citing the coelacanth as an example. According to paleontological records, coelacanths became extinct at the end of the Cretaceous period, 70 million years ago. However, this Conclusion had to be revised when living coelacanths were discovered near Madagascar. Steady-state advocates argue that it is only by studying extant species and comparing them with fossils that one can draw Conclusions about extinction, though even in such cases, the probability of error remains high. Using paleontological data to support the steady-state theory, its supporters interpret the appearance of fossils as the result of ecological events. For instance, they explain the sudden appearance of a fossil species in a particular stratum by an increase in its population size or its migration to an area offering favorable conditions for fossilization.