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Nature study Deep Diamond With Perovskite

Deep into the Earth: diamonds and surficial carbon down to 800 km depth in the Earth’s lower mantle.

A team of geologists from Italy (University of Padova, University of Pavia and CNR-IGG Padova), Canada (University of British Columbia and University of Alberta), UK (University College London), and South Africa (University of Cape Town and Rhodes University) definitively proved what geophysicists indirectly predicted so far, i.e. the oceanic crust and surficial carbon can reach the lower mantle (below 660 km depth) by subduction processes.
The discovery, published in Nature was possible thanks to the study of a special “super-deep” diamond from the famous Cullinan mine (South Africa), where the world’s largest 3107-carats Cullinan diamond was found more than 140 years ago. In detail, the research team, including Dr Martha Pamato from the Department of Earth Sciences at UCL, discovered, the first natural CaSiO3 mineral with a perovskite crystal structure still trapped within the diamond. Many deep Earth scientists had predicted that this mineral would never be found at the Earth’s surface, even though there are zetta tonnes (1021 tonnes) of this material buried deep in the Earth. This very high-pressure form of calcium silicate (CaSiO3) can be stable only from about 600 km depth in Earth’s mantle, continuing to be stable right through the lower mantle. This specific inclusion within diamond shows a chemical composition which would indicate that the diamond formed at about 780 km depth in the Earth’s lower mantle and, at the same time, that the inclusion is derived from oceanic crust (see the cartoon). The research team analysed the carbon forming the diamond, and this indicates its surficial derivation. The discovery is the first definitive prove of oceanic crust and surficial carbon recycled by subduction into Earth’s lower mantle as predicted by seismic images and geodynamic modelling.


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The exploration of icy bodies in the outer solar system by in-situ space-craft investigation has transformed our knowledge of these objects, from points of light to dynamic worlds, each with a unique and rich geological history. Amongst just a few of the largest icy satellites of Jupiter and Saturn we observe great diversity: there is Callisto, an object which seems scarcely to have differentiated and to have experienced little endogenic activity; Ganymede is differentiated, with a liquid iron core generating an intrinsic magnetic field, and a surface moulded by a billion years of extensional activity and cryovolcanic flooding; Titan has a low-density core, consisting of either a rock-ice mixture or hydrous silicates (there is no iron inner core, and no intrinsic magnetic field), and yet it has undergone considerable outgassing to create its dense atmosphere, which in turn is the medium for a global photochemical factory that deposits liquid hydrocarbons and solid organic sediments onto the surface. In all three cases, there is evidence for the existence of global oceans of liquid water buried under 10s or 100s of kilometers of ice.

Internal structures of Jupiter’s largest icy satellites, Ganymede and Callisto, inferred from gravity and magnetic field data acquired by the Galileo space-craft.

Whilst these subsurface oceans are of interest in the search for extraterrestrial life, they also play a pivotal role in the thermal evolution of the host body; they allow efficient convective heat transport, concentrate tidal dissipation in the overlying crust, release latent heat as they cool and crystallise, and provide a source of liquid to be intruded into the crust and extruded onto the surface. In order to interpret the observed surface morphologies of icy satellites and to understand their thermal evolution, geophysical models of their interiors must be constructed, which, in order to be accurate, require the properties of the constituent materials be known in the pressure and temperature range of relevance. These include the phase diagrams, equations of state and transport properties of both liquid and solid phases, many of which are poorly known, if at all, for the relevant materials under the conditions extant inside icy satellites.

In addition to providing the planetary science community with a critical basis for developing models of icy satellite interiors, the materials property data are also of value for their contribution to understanding the behaviour of small molecules under high pressure, which in turn yields important information on hydrogen bonding. The effects of even modest pressures – a few GPa – on the hydrogen bond are dramatic, allowing us to probe the potential energy surface across a broad range of thermodynamic parameter space, data that are used to refine highly accurate quantum mechanical simulations of hydrogen bonding. This information is applied to predicting the functional properties of biomolecules, such as protein-ligand complexes, and to predicting the structure of novel crystalline polymorphs of pharmaceutical materials.