IAP-24-066

How did Earth become a habitable planet? Revealing the origins of Earth’s water using Antarctic meteorites

The question of the source of Earth’s oceans is controversial. Our planet cannot have had liquid water when it initially formed 4600 million years ago because it would not have been stable on a surface that was hot and being continually bombarded by meteorites. The oceans formed later, with water possibly being sourced from degassing of Earth’s interior [1]. Alternatively, water could have been imported from beyond our planet, and delivered by a rain of solar wind irradiated interplanetary dust particles [2] and/or by torrents of meteorites and comets that were themselves derived from the cold and dark outer reaches of the Solar System where water-rich asteroids reside at the present-day [3]. Answering this question is important to our understanding of Earth’s distant past and the evolution of life, to predicting whether oceans were once present on other terrestrial planets, and for evaluating the potential for exoplanetary water worlds.

The significance of this question is underscored by the recent NASA and the Japan Aerospace Exploration Agency (JAXA) missions that successfully collected and returned samples of the primitive carbonaceous asteroids Ryugu and Bennu, respectively [4]. A primary goal of both missions was to study these bodies as potential reservoirs and sources of the water and organic compounds that were likely to have been so crucial to the origins of life on Earth.

Despite the huge scientific importance of these returned samples, they represent only two out of the huge number of water- and organic-rich carbonaceous asteroids. Thus, this project will seek to understand the source of the bioessential compounds that made Earth a habitable planet using carbonaceous chondrite meteorites that have been collected from Antarctica [5]. Hundreds of meteorites are available to study and probably sample a wide variety of water-rich carbonaceous asteroids. Although their water content can be readily quantified, in order to correctly interpret the data we have to be able to compensate for contamination of the meteorites during their time in Antarctica. Sources of contamination include adsorption of water from the atmosphere, but also growth of new water-rich minerals. Although this terrestrial overprint could be regarded as a hinderance to exploring the origin of Earth’s water, it will have its own benefits in enabling us to understand how meteorites are affected by the Antarctic environment more broadly so that extraterrestrial compounds and minerals can be confidently distinguished from those of an extraterrestrial origin. The end-product of this project will be a comprehensive model describing the role of primitive asteroids in making Earth and other terrestrial planets habitable worlds.

The main analytical techniques will be optical and electron microscopy, electron probe microanalysis, X-ray computed tomography, stepwise pyrolysis, thermogravimetric analysis, mass spectrometry, X-ray photoelectron spectroscopy. This work will be undertaken in Glasgow and St Andrews, with collaborations anticipated with national analytical facilities (e.g., SUERC) and relevant research organisations (e.g., Natura History Museum, London).

Year 1

Year 1: Literature review on early Earth, origins of life, and the structure and composition of the asteroid belt. Selection of a suite of meteorites from the NASA Antarctic collections and loan requests. Training in mineralogical, chemical, and isotopic techniques for analysis of meteorites using currently available samples. Initial characterisation of the meteorite chips and thin sections once received by optical microscopy and X-ray computed tomography.

Year 2

Year 2: Characterisation of the mineralogy of meteorites in thin section by electron microscope imaging and quantitative microanalysis. Measurement of the concentration and hydrogen isotopic composition of water evolved from Antarctic meteorite samples by stepwise pyrolysis-mass spectrometry

Year 3

Measurement of the concentration and composition of gases evolved from Antarctic meteorites by thermogravimetric analysis and mass spectrometry. Characterisation of the surface properties of samples by X-ray photoelectron spectroscopy and experiments using isotopically labelled water.

Year 3.5

Writing up of thesis, submission of papers, and presentation of results at international conferences

The student will be trained in a wide variety of skills including: Meteorite identification and characterisation; the geology, climate and environment of Antarctica; analysis of geological materials by electron beam and X-ray techniques (scanning electron microscopy, electron probe microanalysis, X-ray computed tomography, X-ray photoelectron spectroscopy), public communication of science, presentation of results at UK and international conferences