Graph of radiocarbon dating
Fortunately, scientists have developed several methods that not only circumvent the difficulty of not knowing the original amounts, but also provide a very reliable means of statistical validity checking.
Radioactive decay is in turn a very basic physical phenomenon, well understood as a consequence of quantum mechanics.
The half-life T of this decay has been measured in careful laboratory measurements as T = 48.8 billion years.
On the other hand, strontium-86 is a stable isotope.
Note how breathtakingly close these points are to the fitted lines (thus confirming with high statistical confidence the validity of the resulting dates): The data for the first graph (upper left) is a set of measurements of basaltic achondrites (meteorites) in [Basaltic1981, pg.
938]; the data for the second graph (upper right) is from early Archaean gneisses rocks near Isua, Greenland [Morbath1977]; the data for the third graph (lower left) is from ancient gneiss rocks in Swaziland [Carlson1983]; the data for the fourth graph (lower right) is from lunar dunite rocks gathered during Apollo 17 [Papanastassiou1975]. For many years, fairly large samples were required to produce statistically reliable results.
Of course, in real scientific research, scientists do not rely on manually drawing points on graph paper to determine a best-fit straight line or to determine the line's slope or y-intercept.