The Strength of the Lower Mantle

The internal behaviour of the Earth is controlled by convection hence knowledge of mantle viscosity is critical to our understanding. The viscosity of the mantle on large scales has been measured from post-glacial rebound and geoid inversions. These have shown that there is a significant contrast in viscosity between the upper and lower mantles which has been invoked to explain the varied behaviour of subducting slabs at the 660 km discontinuity. The slabs show a range of behaviour from ponding just above the 660 km discontinuity to penetrating the discontinuity and thickening as they enter the lower mantle.
It is apparent therefore that the size and impermeability of the 660 km viscosity contrast affects the style of mantle convection and cooling rates but the resolution of the geophysical observations is not sufficient for a complete understanding of the fate of material around the 660 km discontinuity. Here we propose to measure the rheology of the minerals and assemblages present in the transition-zone and lower-mantle and so provide the constraints needed for a fuller understanding of the viscosity contrast between the upper and lower mantles.

Academic users: We will integrate our work into the recently established Paris-UCL Research Exchange (PURE) programme which aims to foster collaboration between scientists working on the deep Earth (both mantle and core) at UCL and at the Institut de Physique du Globe de Paris. Broader engagement with material scientists will be made through the UCL Centre for Materials Research, on which Dobson is a board member.

Training: The project will result in the training of one PDRA and the continued training of the Research Co-I Hunt. The PDRA will be trained in high-pressure/high temperature experimental techniques (mostly Liverpool University), measurement of physical properties and diffraction studies, and will also gain experience working at international large-scale facilities (e.g., NSLS); as a result s/he will be in a position to gain employment in a variety of materials science based occupations. As part of their training, both PDRAs will be required to participate in courses, as part of the staff development programmes at their respective universities, which continues the Robert's Agenda in our institutions.

Industry Dobson will continue his work with the fine-arts industry to develop improved paper registration techniques. One day meetings will be held annually to discuss progress and further developments.

Outreach - There is an existing outreach programme run by UCL Earth Sciences to which the investigators from UCL already contribute; the PDRAs working on this project will be expected to participate in this activity. In addition, we shall our research activity, "Diamonds from Dirt", aimed at key-stage 3 students. Diamonds can be readily grown from any source of carbon; we have already grown diamonds from toast with work-experience placements. We believe that growing diamonds from 'snot' will engage with younger students. While this might seem flippant we genuinely believe it is of vital importance to capture the imaginations of students at as young an age as possible and this should appeal broadly, involving a 'girl's best friend' and, possibly, a young boy's best friend. Nasally secreted mucus is a mixture of water and glycosylated peptides: once dried it has a high concentration of carbon (about 30 mole%) and, after reducing pyrolysis, will readily form diamonds via the standard solvent catalysis route. It will not be possible, for health-and-safety reasons, for key-stage 3 students to attend the synthesis experiments so we propose to make a web-cast of the diamond growing process which we will use in conjunction with school visits to discuss the process and present the grown diamonds. These outreach activities will be performed in collaboration with Dr Andrea Sella (UCL Chemistry) who is an EPSRC senior media fellow and has contacts with a network of primary schools in London, including being a governor of Gilmore Primary School and running several science clubs. We also strongly suspect that a webcast about growing diamonds from snot might be picked up by the news media, allowing us to discuss more serious aspects of high-pressure research and public outreach.