Cosmogenic nuclide dating
(The circle on the localization map indicates the studied area; red numbers, number of the sample in Table 2.) The Toumaï cranium is precisely located in the TM 266 section.(Toumaï) (1, 2) have changed substantially the understanding of early human evolution in Africa (1–4).This provides an ideal method for determining when a glacier retreated from a region, hence exposing the ground beneath.Technological developments in the last few decades have allowed more precise measurements of their concentration in terrestrial rock samples and this dating technique is becoming increasingly popular.This disparity between dates determined by different dating methods and the large spread of TCN ages suggests that the cobbles and boulders have considerable inherited Be concentrations, suggesting that the clasts have been derived from older shorelines or associated landforms.These results highlight the problems associated with using surface cobbles and boulders to date Quaternary surfaces in Death Valley and emphasizes the need to combine multiple, different dating methods to accurately date landforms in similar dryland regions elsewhere in the world.
The total concentration of these isotopes in a rock surface therefore represents the length of time that the surface has been exposed to the atmosphere.
The base of the mapped sections consists of a well developed, thick, aeolian facies (8). U.) is composed of poorly cemented sand and argillaceous sandstone alternation characterized by dense networks of root tubules/root molds (palaeosols) and termite nests (9, 10). The uniform stratigraphy at the TM localities allowed us to use absolute ages from both TM 266, where Toumaï was discovered, and TM 254 to assign an age to Toumaï.
It was hoped that the tephra layer would contain material datable by the Be associates with continental particles, where it decays with a half-life of ≈1.4 million years.
Novel applications of multiple nuclides with different half-lives are also being developed for determining ages of timing and amounts of soil erosion in the past, with potential applications to archaeological settings (see below).
Ar/Ar dating is limited to K-rich minerals, such as sanidine, from volcanic ashes and is primarily used to bracket the timing of site occupation.