Chemical evolution of the terrestrial planets

1585 lava flow, La Palma, Canaries

We study the ~4.5 billion year history of the terrestrial planets of our solar system, from the stellar synthesis of the elements of which they comprise through their accretion and re-organisation by differentiation to their current architecture.

We use isotopic measurements to fingerprint different modes of nucleosynthesis, to time and determine rates of accretion and differentiation and to trace the large-scale elemental cycling on Earth. These aims are part of the wider interests of the Planetary Sciences Group which involves researchers from Earth Sciences, Physics and Chemistry.

Early Solar Nebula History

So-called mass independent isotopic measurements (for example of Ti, Ni and Mo) provide invaluable fingerprints of the stellar sources that contributed to the solar system. We are interested in the different stellar contributors to the solar system, how this influenced accretion in the solar system and in turn how the heterogeneous distribution of this material between different meteorites informs on the processes occurring in the early solar nebula.

The timing and duration of the accretion of meteorites and their precursors (e.g. chondrules) is a key part of this story and we have developed several extinct isotope systems (e.g. 26Al – 26Mg) to this end.

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Planetary Differentiation

The large-scale architecture of planets is imposed early in their history but is also susceptible to later modifications. In simple terms planets split into core mantle and crust, but on Earth, where this can be studied in more detail, additional complexities are evident. We are interested in constraining the timing of such differentiation events and the character of the reservoirs involved. We have identified the very early formation of cores on planetesimals and have investigated evidence for any on-going interaction of the core with the overlying mantle.

We have expended a deal of effort in understanding the growth of the continental crust on Earth, notably from the in situ measurement of isotopes in single mineral grains, and as a consequence the complementary evolution of the mantle. Many of our endeavours in planetary differentiation are aided and abetted by the local expertise in experimental petrology provided by BEEST.

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Global Element Cycles

Terrestrial mantle convection, as manifest on the surface by plate tectonics, results in the recycling of elements on a planetary scale. Melting preferentially brings some elements to the surface, weathering can differentially move elements from land to sea, where interaction with the oceanic crust can lead to their ultimate return to the mantle via subduction.

The operation of these cycles link the huge reservoir of the mantle with the habitable outer layer of the Earth. The processes and fluxes involved are crucial to our understanding of the maintenance of our environment.

We use isotopic tracers that are fractionated in the hydrosphere to trace material that is recycled through the mantle. We are interested in the operation and changes of element cycles on the billion year timescale but the understanding gained is of significance to the shorter timescales of interest in our research into Global Change.

Fieldwork on the Mariana Islands (W. Pacific)
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