Although this column and its ‘age’ was firmly settled well before the advent of radiometric dating, the latter has been used to quantify the, ‘ages’ of the strata and the fossils in the column, so that in many people’s minds today radiometric dating has ‘proved’ the presumed antiquity of the earth.
However, it is important to remember that all radiometric dating methods are based on three main assumptions:— The highly speculative nature of all radiometric dating methods becomes apparent when one realizes that none of the above assumptions is either valid or provable.
One such geological setting that yields these false U -Th -Pb ‘ages’ and ‘isochrons’ is the Koongarra uranium deposit and the surrounding area (Northern Territory, Australia). Local geology map showing the location of the Koongarra No. describes the Koongarra uranium deposit and the area’s local geology (see Figure 2).
The Koongarra uranium deposit occurs in a metamorphic terrain that has an Archaean basement consisting of domes of granitoids and granitic gneisses (the Nanambu Complex), the nearest outcrop being 5 km to the north (see Figure 1).
But the method does not always give the ‘expected’ results, leading to fundamental questions about its validity.
This alteration extends for up to 1.5 km from the ore in a direction perpendicular to the host quartz-chlorite schist unit, because the mineralisation is essentially stratabound.
The outer zone of the alteration halo is most extensively developed in the semi-pelitic schists, and is manifested by the pseudomorphous replacement of biotite by chlorite, rutile and quartz, and feldspar by sericite.
Silicification has also occurred in fault planes and within the Kombolgie Formation sandstone beneath the mineralisation, particularly adjacent to the reverse fault.
Put simply, none of these assumptions can have been observed to have always been true throughout the supposed millions of years the radioactive elements have presumed to have been decaying.
Of the various radiometric methods, uranium-thorium- lead (U-Th-Pb) was the first used and it is still widely employed today, particularly when zircons are present in the rocks to be dated.