llenged their beliefs (Chancellor, 1973, p.41). It was not until the publication of Charles Darwin's The Origin of Species that the discussion of evolution was revived.When non-biologists talk about biological evolution they often confuse two different aspects of the definition. On the one hand there is the question of whether or not modern organisms have evolved from older ancestral organisms or whether modern species are continuing to change over time. On the other hand there are questions about the mechanism of the observed changes... how did evolution occur? Biologists consider the existence of biological evolution to be a fact. It can be demonstrated today and the historical evidence for its occurrence in the past is overwhelming. However, biologists readily admit that they are less certain of the exact mechanism of evolution; there are several theories of the mechanism of evolution.EVOLUTION AND FOSSIL RECORDIn the study of human evolution, two main methods of dating are used: Carbon-14 and potassium-argon dating. Carbon-14 dating involves the decay of radioactive C-14, which has a half-life of 5770 years. This makes this method useful for dating of recent fossils, with good accuracy, up to 50,000 years back. After 5770 years, half of the carbon-14 in a fossil decays to nitrogen-14. Since the ratio of carbon-12 to carbon-14 in a living organism remains the same as in the environment around them because the organism constantly eats and replenishes it, if it were to die, the ratio would change greatly after many years. It is the difference between this ratio now and the time is died that allows a date for it to be established.Potassium-argon dating, another dating method, is possible due to volcanic ash and rocks found near many fossil sites. Rocks and ash created in this manner contain potassium-40, but no argon. As time passes, the potassium-40 decays into argon-40. In the laboratory, the sample is reheated, and since argon-40 is...
