Since the cosmic ray spallation route is the only possible source of beryllium-7 and beryllium-10 occurrence naturally in the environment, they are therefore cosmogenic.Here is a list of radioisotopes formed by the action of cosmic rays; the list also contains the production mode of the isotope.The sedimentary unit from which Toumaï was unearthed was named the anthracotheriid unit (A. also contains a mammalian fauna that includes taxa that are more primitive than the Lukeino fauna [Kenya, dating from 6 Ma ago (6)] and similar to the fauna from the lower Nawata Formation of Lothagam [Kenya, 6.5–7.4 Ma ago (7)].
The magnitude of the latter process is tightly linked to the geochemical and the hydrogeological contexts at the time of the sedimentary deposition.
To apply the radioactive decay equation described above, it is thus essential to know the regional initial authigenic Be ratio.
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.
(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).If these requirements are met, then Be reported for surface marine sediments (14, 16), for top surfaces (or extrapolated to zero age) of Fe-Mn deposits (17–23), for present-day deep waters in the Atlantic, Pacific, Indian Ocean, and Mediterranean Sea central basins and margins (13, 24–30) mostly range between 0.5 × 10Be ratio can be expected considering that in continental systems, the two major processes affecting the aqueous geochemistry of beryllium are dissolution from rocks and uptake onto particles (13).The initial authigenic Be ratio thus depends both on the lithology of the region drained and on the partitioning between solid and aqueous phases.Sequential leaching procedures have been developed to selectively extract this authigenic component for dating purposes (14).It has effectively been demonstrated in marine systems that the can be accurately estimated, and the second is that the selected samples must have remained “closed” to entry or loss of the cosmogenic isotope and its normalizing isotope.It is first necessary to find some method of normalizing Be is from detrital input, of which a small fraction is dissolved (12, 13)], it has been shown that, in suitable instances, the dissolved beryllium isotopes are homogenized before deposition and that their ratio is a useful chronologic tool.