The violent making of the Earth - exploring the birth and infancy of a terrestrial planet using isotope geochemistry

This project aims to estimate the chemical composition of the Earth, which will contribute to our understanding of how it was formed. Knowing the chemical composition of the Earth is a fundamental parameter to almost every model in natural science, such as climate, atmospheric, oceanographic or solid Earth research. When estimating the composition of the Earth, scientists are facing a dilemma. We only have access to the very top part of the solid Earth, also called crust, which makes up only 0.5% of its mass. The remaining 99.5% are represented by the Earth's mantle and core and are beyond our reach, often buried more than 100km below the surface. Estimating the chemical composition of the entire Earth is therefore a complex and daunting task, fraught with large uncertainties, but essential to questions such as the Earth's contents of precious metals and how the key ingredients to life, particularly carbon and water, were delivered to our planet.

The Earth grew by collisions with its neighbouring planetary bodies some 4.6 billion years ago. The energies involved in these violent impacts were sufficient to melt the entire growing planet causing dense molten iron to sink to the centre and to form the Earth's core. Together with the iron, this process also stripped all precious metals, like gold and platinum, from the mantle leaving it devoid of these elements. After about 100 million years, these planetary collisions ceased and gave way to low-energy impacts of smaller asteroids. It has been suggested that this late asteroid shower, also called 'late veneer', not only delivered most of the ingredients essential for life, but also replenished the precious metal content of the mantle.

Some of the asteroids escaped incorporation into planets and have been circling the Sun unharmed for nearly 4.6 billion years. They therefore represent remnants of the building blocks that formed the Earth. Fragments of such asteroids are still falling to Earth as meteorites. They hold important clues as to what the bulk composition of the Earth was, before it separated into a core, mantle, and crust.

Over the past 40 years, the view persisted that the Earth has, on average, a chemical composition similar to that of meteorites. However, recent research showed that the rocks on Earth show a relative enrichment in the isotope 142-neodymium compared to these extraterrestrial rocks. It is therefore possible, that the Earth also has a completely different chemical composition. If true, our current models for the formation and evolution of the Earth have to be fundamentally revised.

Here, I will follow a different and novel approach of exploring this question: If one would know the composition of the crust, core, and mantle, one could simply 're-constitute' them into the composition of the whole Earth. Rocks of the crust are accessible and we know their composition. Based on geophysical evidence we also know the size of the core and we can estimate that it consists of almost 100% iron. The vital information that is still missing, is the composition of the mantle! I have developed two new analytical methods that will allow me to answer exactly this question. I will use them to measure lavas that originated in the mantle and erupted on the seafloor. For the first time, it will be possible to estimate the composition of the mantle and to calculate the composition of the Earth. The result will tell me, what the composition of the Earth's building blocks was and, ultimately, allow me to explore how the Earth was formed. Yet, I can take these studies a step further. My measurements will also show, how the precious metal-rich 'late veneer' was stirred back into the mantle and to what degree alternative explanations, such as leaking of hot iron melt from the core into the mantle, are alternative explanations of why the precious metals are so surprisingly "abundant" today.

The results of this study and the new methods that are to be applied will be of interest not only to academics but also to the general public, industry, and policy makers:

1) Press/Media/Museums/Science education/Lay scientific organisations/Wider public

The massive media attention that followed the publication of my most recent research on the early geological history of the Earth in the journal 'Nature' demonstrated that my research produces results, which are of interest to the wider public. There is a general public interest in natural sciences, as shown by the large number of popular scientific journals and TV programs in the UK and worldwide. The origin of our planet is a regular theme of such productions. Yet, we still know only very little about this crucial time of Earth's history and, accordingly, new scientific results on this topic are readily embraced by the media.
I anticipate that the new scientific results of the proposed project will contribute to creating an improved public awareness of the processes that play a role in how the Earth and the planets were formed. I know that the press, TV and radio media, as well as lay science organisations are keen on disseminating this information. Therefore, important immediate beneficiaries of the project will be news channels, radio programmes, newspapers, popular scientific journals, scientific TV programs, natural history museums, geography/geology education programs in schools, and lay geologists and meteoriticists associations.

2) Commercial private sector

Industry: Nanotechnology is a fast-growing commercial sector, with an estimated 3 to 4 new products being released to the market every week. The Ce method that I recently developed, and which will be used in this project, can also be applied to the isotopic tracing of engineered CeO2 nanoparticles, based on radiogenic differences in their isotopic composition. This application will be developed in collaboration with Dr Mark Rehkämper and may be of great interest for this industry sector.

Mining companies: An immediate result of the study will be to what extent the resources of precious metals that we find today in ore deposits, are due to the addition of meteoritic material to the early Earth. As such, the outcomes of this study will be of wider interest to commercial companies dealing with the mining of precious ore resources.

3) Policy makers

With the increased concern about manmade climate change, it is essential to understand the natural response of Earth systems to rapid climate change in the past, in order to predict what might happen in the future. Such future scenarios, based on high-quality data and open scientific findings, are integral to policy decisions about climate change prevention and mitigation. One of the methods that I recently developed, and which will be used in this project, will be applied to improve palaeo-oceanographic and palaeo-climate models (in collaboration with Dr Tina van de Flierdt). This work will have an immediate impact for the climate research community and this will transmit later to policy makers.