For our topic on radiometric dating and fractional crystallization, there is nothing that would prevent uranium and thorium ores from crystallizing within the upper, lighter portion of the magma chamber and descending to the lower boundaries of the sialic portion. Such mixings can produce arbitrary isochrons, so these cannot be detected by any mixing test. The fossil record is fundamental to an understanding of evolution. Samples are exposed to neutrons in a nuclear reactor. However, the composition of lead isotopes between magma chambers could still differ, and lead could be incorporated into lava as it traveled to the surface from surrounding materials. This is well-established for most isotopic systems. The ratio of the parent to daughter then can be used to back-calculate the age of that rock.
This will, over the assumed millions of years, produce uneven concentrations of lead isotopes.
Why is radioactive dating more accurate than relative dating?
According to plate tectonic theory, continental crust overrides oceanic crust when these plates collide because the continental crust is less dense than the ocean floor. Harper, and David Benton. The upper portion of the sialic magma would be cooler since its in contact with continental rock, and the high melting point of UO sub 2 uranium dioxide, the common form in granite: There are many radiometric clocks and when applied to appropriate materials, the dating can be very accurate. The carbon dating limit lies around 58, to 62, years. United States Geological Survey.