Because the time it takes to convert biological materials to fossil fuels is substantially longer than the time it takes for its 14 C to decay below detectable levels, fossil fuels contain almost no 14 C , and as a result there was a noticeable drop in the proportion of 14 C in the atmosphere beginning in the late 19th century. Methods for Determining Past Climates.
Email already in use. Another example is driftwood, which may be used as construction material. The advent of radiocarbon dating may even have led to better field methods in archaeology, since better data recording leads to firmer association of objects with the samples to be tested. In addition, a sample with a standard activity is measured, to provide a baseline for comparison. In nature, carbon exists as two stable, nonradioactive isotopes: The existing carbon within the organism starts to decay back into nitrogen, and this starts our clock for radiocarbon dating. So, you might say that the 'full-life' of a radioactive isotope ends when it has given off all of its radiation and reaches a point of being non-radioactive.