The project seeks to uncover evidence to constrain the two largest scale events in the history of the Earth. One focus of attention is the crystallisation of a primordial magma ocean, which is believed to be an inevitable initial stage of the planet following its energetic accretion. Do any vestiges of this event remain or have subsequent processes removed all record of this tumultuous beginning? The second main objective is to determine when the signature process of the Earth, plate tectonics, commenced.
These are ‘blue skies’ science questions but seek understanding of the fundamental processes that shape our unique planet. As such, we believe the answers are of intrinsic interest to all.
We will use new tools and technologies to tackle these difficult problems. So we have initial objectives in a) refining our ability to analyse the isotopic compositions of the main element constituents of the outer Earth (silicon and magnesium), which can preserve a record of magma ocean crystallisation b) developing a means to date single grains of potassium feldspar, one of the major minerals of the Earth’s crust, that have been eroded and accumulated in sedimentary rocks. Such grains provide a representative sample of the Earth’s crust through time, but need to be dated in order to be used. We will employ novel methods to allow these ages to be determined.
Once our analytical tools are developed we will look for diagnostic differences in the Mg and Si isotope compositions of a range of samples of mantle to look for residual signatures of the magma ocean. We expect this evidence, if still present, to be stored in the deep mantle. This part of the Earth can be indirectly accessed by studying melts generated from upwelling mantle plumes, such as beneath volcanically active islands such as Iceland. For the potassium feldspar grains we will combine our innovative dating methods with further analysis of the Pb isotopic compositions on the same grains, which carry a diagnostic signature if the formed through processes intrinsically associated with plate tectonics. These combined measurements will therefore track the history of plate tectonics. Ultimately we will use dynamic models of the Earth’s surface and interior to model our isotopic compositions and so obtain holistic view of how the Earth functions.
