The main objective of my Ph D is to reconstruct the retreat of the Uummannaq Ice Stream System, a large system of coalescent ice streams in West Greenland.To constrain the timing of the retreat of this ice, we are using a technique known as cosmogenic nuclide dating.Some are formed by neutron capture events, others by spallation, where a high-speed projectile knocks various components out of the targets' nucleus, leaving several differnt nuclei in its place.The following radioactive nuclides are being continually created on Earth by cosmic ray bombardment, acting on target nuclei either in dust particles in the upper atmosphere, or to a lesser extent, on exposed rocks at the Earths surface where fewer cosmic rays are able to penetrate: The main nuclear processes involved in the creation of cosmogenic nuclides are spallation, muon capture (similar to electron capture) and neutron activation.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.
For instance, the beryllium-10 production rate (as shown by ice-core records) trebles during sun-spot minima, with the greatest variation being experienced at the highest latitudes (the Poles of the Earth) and the least variation at the Equator.
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.
(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).
Cosmic rays, originating from outer space, bring rare cosmogenic nuclide isotopes (I am using Aluminium) to the Earth’s surface, where they build up in exposed rock surfaces at known rates.