“Earth”
The scientific approach taken by the LPG since its creation is based on the motto “Understanding the planets using tools and knowledge developed on Earth and vice versa”. Over the past few years, we have been able to contribute new results in relation to other planets and their satellites using skills acquired across a range of different Earth Science domains. The work carried out within the theme Earth corresponds to the reciprocity referred to in the motto: we use expertise developed within the field of planetology in order to devise new methods of study and analysis on Earth. The aim for this theme, therefore, is to promote the emergence of original study topics through our experience in planetology over the coming years, with this ranging from internal dynamics to the evolution of the surface of the Earth. Our work currently has three primary research axes:Structure and dynamics of the Earth, Interactions between liquids/rocks/life and Risk and environment.
1. Structure and dynamics of the Earth
This research axis groups together our work on the physical and chemical structure of the interior of the Earth and on the way in which its different layers interact. We develop models of the interior of the Earth in terms of its elastic and/or magnetic properties, which impact upon the processes for exchanging matter and energy. Numerical modelling and methodological developments play a significant role in this regard. Equally, the work carried out in order to analyse chemical transfers has made it possible to quantify exchanges of matter and to map out the history of the interior of our planet.
1.1 Observing and modelling the Earth’s internal structure
We study the internal structure of our planet, primarily using seismological and magnetic observations in addition to numerical modelling:
– Elastic, isotropic and anisotropic properties of the Earth’s crust and mantle, constrained by seismic tomography, regional and global; Extraction of seismic information in signal noise.
– Modelisation of the internal magnetic field and its temporal variation (SWARM mission): Mathematical separation of internal and external contributions; Geometry of the external magnetospheric and ionospheric fields – seasonal variations, the electrical conductivity of the mantle; Lithospheric field – continental reconstruction over geological times.
1.2 Internal dynamics and coupling
The Earth’s internal interactions and dynamics are assessed using their mechanical, thermal, chemical and magnetic properties:
– Mantle convection and thermal heterogeneity of the core-mantle boundary.
– Influence of core-mantle thermal interactions on the geodynamo – field morphology, reversals…
– Deep origin of low-intensity anomalies in the magnetic field on the surface of the Earth
– Chemical transfers between the different layers of the Earth. Cycle of volatile and chalcophile elements: Redox coupling between the surface and the interior, characterisation of volcanic degassing.
2. Interactions liquids/rocks/life
This research axis focuses on the role of physical and chemical interactions between liquids, rocks and living organisms as well as the impact they have on the evolution of the surface and the sub-surface of the Earth. We work, on one hand, on the mechanical aspects of these interactions (the geomorphological and structural transformations of geological materials caused by liquids), and on the other hand, on their chemical and mineralogical aspects (physicochemical transfers, alteration and mineralisation in response to interactions between liquids, rocks and living organisms).
2.1 Geomorphological and structural transformations of geological materials caused by liquids
To understand the mecanical couplings between fluids, deformations and transfers of matter in porous medium at Earth’s surface, we study the phenomena of destructuring, clogging, channelling of rocks, and more generally changes to their rheology (fracturing, brecciation, fluidisation, dissolution, etc.). Our research objects include:
– Ancient sedimentary basins (altered by liquid overpressure linked to sedimentary overloading and to phase changes in the organic matter).
– Sub-glacial environments (role of circulation of pressurised interstitial liquids under erosion, sedimentary transfer and the shaping of reliefs).
– Karst environments (morphological evolution by circulation of surface and underground water).
2.2 Chemical transfers, alteration and mineralisations
This research axis brings together two of the LPG’s areas of expertise: Processes of alteration and mineralisation on the surface of planets and bio-physico-chemical transfers on the surface of the Earth. It focuses on the physico-chemical evolution of surface geological materials (rocks, regolith, sediment, soil, ice). Among these various interactions, we are working on three specific issues:
– Development of spectral infrared criteria to identify the geological origin (hydrothermal circulation and continental alteration) of minerals (phyllosilicates and silica).
– Role of live organisms (microbial agents and macro-organisms) in the processes of alteration and biomineralization.
– Role of glaciers and their meltwater as mineralization environments (sulfates, chlorides, nitrates, carbonates, etc.).
3. Risk and environment
This research axis studies the environmental disruptions and risks arising from human-induced global changes, in particular pollution by contaminants (metals and radioisotopes), and ways to address them. Our work focuses on (i) in-situ observations and tracing of contamination sources (natural and anthropogenic materials), studying their physico-chemical characteristics and their mobility, (ii) environmental modifications and biomonitoring, (iii) the development of remediation technologies such as the synthesis of containment matrices and soil rehabilitation.
3.1 Metal dynamics in soil-water-plant continuum
We develop three approaches to describe environmental impregnation and its dynamics:
– Spatial study of metals and identification of their origins.
– Evaluation of their mobility and toxicity in the environment: speciation and associated isotopic fractionation.
– Role of organic complexing agents involved in remobilization processes.
3.2. Environmental impact of contamination and biomonitoring
Our work focuses on terrestrial and marine organisms using three approaches:
– Evaluation of the role of contamination on soil and sediment microorganisms (abundance, genetic diversity) using environmental DNA approaches.
– Incorporation of contaminants into bivalve shells, evaluation of the role of the life cycle.
– Comparison of contaminant levels in bivalve shells and monitoring networks.
3.3 Remediation for radioisotopes and metals: immobilization and extraction
Development of innovative remediation solutions for soils and immobilization of pollutants in specific matrices:
– Synthesis and characterization of inorganic materials (glasses and vitroceramics) doped with radioisotopes and/or metals with the aim of long-term geological confinement.
– Nature-based solutions: phytoextraction of metals, associated with bioaugmentation of soils by bacteria.
– Monitoring of the physico-chemical and biological alteration of these matrices in natural conditions.