By 2020, carbon emissions will start to affect the technique, and by 2050, new organic material could be indistinguishable from artifacts from as far back as AD 1050, according to research by Heather Graven, a lecturer at Imperial College London.The technique relies on the fraction of radioactive carbon relative to total carbon.Other critics, perhaps more familiar with the data, question certain aspects of the quality of the fossil record and of its dating.These skeptics do not provide scientific evidence for their views.To give an example if a sample is found to have a radiocarbon concentration exactly half of that for material which was modern in 1950 the radiocarbon measurement would be reported as 5568 BP.For two important reasons, this does not mean that the sample comes from 3619 BC: Many types of tree reliably lay down one tree ring every year.If greater likelihood is sought, we could look at the interval 30 \pm 80$ years, encompassing two standard deviations, and the likelihood that the half-life of a given sample of Carbon $ will fall in this range is a little over $ percent.
In the past 150 years they have not found any fossils that Darwin would not have expected.
The wood in these rings once laid down remains unchanged during the life of the tree.
This is very useful as a record of the radiocarbon concentration in the past.
Radiocarbon measurements are always reported in terms of years `before present' (BP).
This figure is directly based on the proportion of radiocarbon found in the sample.