After estimating the rate of this radioactive change, he calculated that the absolute ages of his specimens ranged from 410 million to 2.2 billion years. Wasserburg applied the mass spectrometer to the study of geochronology.
Though his figures were too high by about 20 percent, their order of magnitude was enough to dispose of the short scale of geologic time proposed by Lord Kelvin. This device separates the different isotopes of the same element and can measure the variations in these isotopic abundances to within one part in 10,000.
Jacobus Henricus van ’t Hoff, one of the founders of physical chemistry.
Next, the electron microprobe bombards a thin microscopic slice of a mineral in a sample with a beam of electrons, which can determine the chemical composition of the mineral almost instantly.
At greater depths the temperature effect should become dominant, and response to stress should result in flow rather than fracture of rocks. Rubey, demonstrated that fluids in the pores of rock may reduce internal friction and permit gliding over nearly horizontal planes of the large overthrust blocks associated with folded mountains.
More recently the Norwegian petrologist Hans Ramberg performed many experiments with a large centrifuge that produced a negative gravity effect and thus was able to create structures simulating salt domes, which rise because of the relatively low density of the salt in comparison with that of surrounding rocks.
Also, by extrapolating backward in time to a situation when there was no lead that had been produced by radiogenic processes, a figure of about 4.6 billion years is obtained for the minimum age of the Earth.
This figure is of the same order as ages obtained for certain meteorites and lunar rocks.
This method has wide applications in, for example, the fields of industrial mineralogy, materials science, igneous geochemistry, and metamorphic petrology.