IAP-24-058

Heavy metal insights into the formation of planet Earth

Our planet is unique. The Earth is the only planet with stable liquid water at the surface, and the only known planet to host life. How did this happen? How do you build a habitable planet? It is vital to answer these key questions if we ever want to figure out how life got started on Earth.
The Earth initially formed as a dry desert planet – very different to the planet we inhabit today. Current theories suggest that most of Earths water, in addition to large quantities of organic material, could have been delivered in the final stages of Earth’s formation from water-rich asteroids, providing the vital components required for life to emerge. Several types of chondritic meteorites derived from water-rich asteroids are a close match to Earth’s ocean’s isotope composition, supporting such theories. However, these same chondritic asteroids are also very different to the Earth both chemically and isotopically in other key components, particularly in the metal loving highly siderophile elements. This presents a challenge and an opportunity.
Highly siderophile elements are key recorders of planetary processes. For example, the unexpected enrichment of highly siderophile elements in Earth’s mantle suggests that primitive chondritic asteroids fell on the Earth during the last stages of planet formation and after planetary differentiation. While the famous global “Iridium layer” at 66 Ma is evidence for the catastrophic impact that wiped out the dinosaurs. Highly siderophile elements can therefore be utilised to trace the addition of chondritic meteorites to our Earth system. However, our understanding of the mineralogical and textural context of highly siderophile elements is limited as these elements are commonly sequestered as nanophase minerals that are challenging to locate and characterise. By increasing our knowledge of highly siderophile element mineralogy in chondritic meteorites will augment our ability to answer key questions regarding planetary formation.
The student will use correlative microscopy to explore the petrology and isotopic composition of highly siderophile bearing minerals in chondritic meteorites to answer the following questions:
1) How does HSE mineralogy, geochemistry and isotope geochemistry vary between ordinary and carbonaceous chondrite meteorites?
2) What do these results tell us about the formation and evolution of chondritic asteroids?
3) Which chondritic asteroid types could really have delivered water to the early Earth?
The project would suit a geologist, (geo-)physicist, or STEM graduate with an interest in Space and Planetary Science. The candidate should be willing to learn several advanced microanalytical tools. The candidate will also gain expertise in meteoritics, planet formation, the structure and evolution of the Earth, and Astrobiology.

The key to understanding highly siderophile elements and their importance in cosmochemistry is by locating the minerals that they are found within, in the rocks themselves. However, highly siderophile elements are low in abundance, and so detailed microanalysis is needed.
The research will use a series of correlated complementary microanalytical techniques to locate Highly siderophile element-rich minerals in chondritic meteorites and characterise them in exquisite detail from the cm scale down to the atomic scale including:
1) X-ray computed tomography will be used to characterise chondritic meteorites in 3D and inform where further sampling of the chondrite will be acquired for higher resolution microanalysis.
2) Scanning electron microscopy and laser ablation inductively coupled plasma mass spectrometry will be used to automate the location of highly siderophile element-rich minerals in chondrites and determine their chemistry and crystallography.
3) Focussed ion beam microscopy will be used to extract very small samples for thermal ionisation mass spectrometry, transmission electron microscopy and atom probe tomography.
4) Thermal ionisation mass spectrometry will be used to constrain the Os isotopic composition of HSE minerals, and potentially date phases using the Re-Os isotope system – this will be undertaken at the University of Bristol.
5) Atom probe tomography to get atomic structure, composition, and isotopes – this will be undertaken at the University of Oxford.
By combining all these datasets together, we will get a clearer picture of the diversity and context of highly siderophile elements minerals in chondritic meteorites and use these data to inform interpretations of planet formation.
The chondritic meteorites and asteroid samples to be studied are already in hand at Glasgow and further samples can be requested if required. The student will get a unique transferrable skillset of advanced correlative microanalysis as well establishing the material properties or resources that are vital for the green economy.

Year 1

This year will involve:
1) A guided literature review on highly siderophile elements in cosmochemistry and planet formation.
2) Training on using the suite of analytical tools utilised by the project including XCT, SEM, FIB, TEM and LA-ICP-MS.
3) Preliminary data collection and honing analytical capabilities focusing on one meteorite group the CM chondrites as a pilot sample.

Year 2

This year will involve:
1) A comprehensive analytical campaign to collect the suite of correlated datasets using all the techniques on a variety of primitive meteorites.
2) Produce a database of HSE minerals in meteorites answering question 1.
3) Presenting initial results at Goldschmidt the premier conference for geochemistry.

Year 3

This year will involve:
1) Synthesis and interpretation of the data generated.
2) Use the data generated to explore ideas around asteroid formation.
3) Calculate how the HSE system on asteroids has evolved over time.
4) Challenge planet formation theories by modelling the HSE component and determine if that is compatible with volatile delivery from water-rich asteroids.
5) The student will with the aid of the supervisory team identify a key result of the thesis and write it up for publication in a peer-reviewed journal.

Year 3.5

The final 6 months will involve writing up the thesis and submission the student will receive support in thesis preparation and writing of work for publication.
This support will also be provided throughout all three years as the student finishes components of the work.

The student will be trained in a series of desirable transferrable skills:
1) Planetary science and materials science. The student will gain a deep understanding of how planets and asteroids form and evolve as well as strong understand of minerals and their material properties.
2) Laboratory skills associated with advanced correlative microscopy.
3) Science writing, communication and presentation skills for publications, conferences and to the general public.