Plate tectonics works like a magician: it can bring deep rocks to the surface, like cards that move from the bottom of a deck to the top. When studying these rocks, you are transported into the world of geological carbon, and explore its links with life.
DeepSeep is a project funded by the European Research Council that focuses on a process called serpentinization. It’s the interaction between the most abundant mineral, olivine, which makes up the vast majority of the Earth's mantle, and water, the most abundant geological fluid on the planet. When they meet, reactions take place, and gaseous energy is created — natural hydrogen, first of all. And if that same water contains carbon, then hydrogen will combine with it to form methane. These energy sources can be used in other geological processes, but also by the micro-organisms that live in the lithosphere. The project’s biggest challenge is to understand how these energy sources, which originate at depths where life cannot exist, are transported to habitable layers of the lithosphere, where micro-organisms can exploit this energy.
The first traces of life we know today date back some 3.8 billion years. And the first evidence of plate tectonics – that is, the framework that would allow this deep serpentinization to create energy sources for life – also seem to date back 3.8 billion years. Our project seeks to identify an environment that could have been particularly fertile for the emergence of life, one that takes advantage of these two peculiarities of Earth – life and subduction – with serpentinization as the link between the two.
This picture is from our last expedition in Mongolia, where we collected about 324 kg of rocks. But the real work begins once the samples are delivered to us, to the Deep Carbon Lab at the University of Bologna. We prepare slides with rock slices 30 thousandths of a millimetre thick: they become transparent and we can observe them with polarising microscopes. This also allows us to observe droplets of deep geological fluids that can get trapped in minerals. We extract these fluids and analyse their geochemical signature, so we can distinguish different types of methane, of biological and non-biological origin, and understand how and why they migrate between different parts of the lithosphere.
The process of serpentinization has been much studied on the surface, but not in the deep Earth, During my studies and work as a researcher at the French National Centre for Scientific Research, in Paris, I also began to investigate processes involving the interactions between rock and fluids. These two areas of research, deep Earth and rock-fluid interactions, met in the DeepSeep project.
Initially, I wanted to better understand the oddities that I had observed over the years while working on rocks, such as unexpected and recurring signs of deep carbon mobilization. But as I delved deeper into the role of geological carbon, these oddities began to make sense and to connect with other areas of study: habitability, life on other planets, and the origin of life itself.
