Diamonds as the key to unravel the origin of Earth's water

Introduction

The origin of Earth's water is still an unsolved mystery in Earth Sciences. Yet, answering this question is paramount in order to validate planetary accretion models and determine the conditions for life-sustainable planets to form.

Importance of D/H Ratio

Comparing Earth's original deuterium-to-hydrogen ratio (D/H) with those of Solar system objects such as meteorites, comets, and the solar nebula can constrain the provenance of water. However, while D/H is precisely determined for extra-terrestrial objects, the exact value for Earth is not known. This uncertainty arises from the fact that Earth's primordial D/H has been lost since its formation due to surface and mantle geological processes.

Challenges in Current Estimates

Current estimates from mantle-derived lavas are challenged by the ability of these samples to retain pristine values. This indicates the need for a pristine reservoir that has remained unaffected over geological time to be found.

Role of Diamonds

Diamonds from the Earth's mantle may be key as they contain trace amounts of hydrogen and are inert and robust time capsules able to survive over several billion years.

Project Goals

The overarching goal of this project is to determine Earth's primordial D/H by investigating the hydrogen content and isotopic composition of a unique set of worldwide, natural diamonds dating from 3.5 to 0.09 billion years ago. This will be achieved using newly-developed, high-precision, and high-efficiency isotope ratio mass spectrometry.

Methodology

The isotopic data will be complemented by atomistic state-of-the-art ab initio simulations to understand the atomic and diffusion behavior of hydrogen in natural diamonds.

Long-term Implications

The new results will be fundamental to pinpoint Earth's water origin, with long-term implications for understanding planet habitability. In a time when international space agencies are actively searching for potentially habitable planets and extra-terrestrial life, this new knowledge will be crucial for understanding the geological and biological evolution of planets in our Solar System and beyond.