Lava rock dating
Related sections Shaping the Earth Related items The geological time scale Dating dinosaurs and other fossils. The rate of creation of carbon appears to be roughly constant, as cross-checks of carbon dating with other dating methods show it gives consistent results.
However, there is a limited range in Sm-Nd isotopes in many igneous rocks, although metamorphic rocks that contain the mineral garnet are useful as this mineral has a large range in Sm-Nd isotopes.
Although we now recognize lots of problems with that calculation, the age of 25 my was accepted by most physicists, but considered too short by most geologists.
For an element to be useful for geochronology measuring geological timethe isotope must be reasonably abundant and produce daughter isotopes at a good rate.Isochron confidence is well founded, for the assumptions of the dating method appear to be internally verified. The y-intercept of the isochron is the initial Sr value and the correspondence to a straight line measures the degree to which the lava has remained a "closed system." "Model dates" have no check for internal consistency. Therefore, Sr as the y-axis would allow the isotope ratios of all rocks in a lava flow to be plotted. Damon, "K-Ar Age of Lava Dam in the Grand Canyon," Geological Society of America Bulletin, 79 (Jan. The Rb-Sr ratios in various rock samples from the same lava flow might differ, but all should plot as a straight line on the graph if the lava was isotopically homogeneous (each rock sample had the same initial Sr ratio) and each rock remained closed to gain or loss of rubidium and strontium since crystallization.
Potassium-40 (Rb has occurred since the rock cooled from the lava flow.