We know that organisms not only populate the Earth’s surface, but also the soil. What is difficult to imagine is that life could even go so far over 10 km deep underground. Yet there is evidence of the existence of microorganisms even at these depths: how is this possible? Their energy sources arewhite hydrogen (i.e. of natural origin and found underground) and the methane resulting from processes of geological origin. These gases are at the center of the laboratory’s research Deep Carbon Lab of the University of Bologna, which arises from the project DeepSeepfunded by the European Research Council (ERC). To study rocks that host natural hydrogen and methane of geological origin, the team led by Alberto Vitale BrovaroneFull Professor of Petrography at the Department of Biological, Geological and Environmental Sciences of Bologna, in recent years he has made expeditions all over the world. These studies are fundamental to the role that hydrogen could play in the origin of life on Earth, as well as in the energy transition as a clean energy source.
How and where hydrogen and methane of geological origin are formed
Natural hydrogen (H2) is free hydrogen, i.e. not bound to other elements to form compounds, which mainly originates during the serpentinization process. This process consists in the transformation of the rocks of the Earth’s mantle, which are peridotites made up of mineral olivinein serpentinites composed of the mineral serpentine. This happens when, at high temperatures and pressuresthe water circulating in the mantle reacts chemically with olivine: in contact with water the iron in olivine oxidises And white hydrogen is released. If carbon is then present, hydrogen combines with it to form methane (CH4).
But what are the areas on Earth where water and mantle rocks can interact? It’s about the subduction zonesin which a lithospheric plate sinks beneath another plate on the ocean floor, giving rise to ocean trenches, and ocean ridgeswhere the rocks of the upper mantle emerge. Recently, near the Mid-Atlantic Ridge, a 1268 m long cylinder of rock was taken from the Earth’s mantle, the deepest ever obtained, in which traces of serpentinization were found. Accessing the rocks of the mantle with drilling is very complicated due to the very high temperatures and pressures, but there are places where the movements of the lithosphere have brought them to light: they are the mountain rangeswhere the research of the Deep Carbon Lab project is concentrated.
The Deep Carbon Lab project and the role of hydrogen in the origin of life
Mongolia, United States, Corsica And Greenland: these are just some of the regions explored by researchers at the Deep Carbon Lab in Bologna, who aim to better understand how natural hydrogen and methane of geological origin (i.e. abiotic, different from that of biological origin) and in how these ascend into the lithosphere to depths compatible with life. To do this, researchers first they collect samples of ancient mantle rocks emerged in correspondence with the mountain ranges. In the laboratory the rocks are then dated and analyzed under a microscope to identify trapped hydrogen and methane bubbles in minerals, which are called fluid inclusions. Through the analyzes of rocks and gases and theoretical simulations it is possible to trace the methods and times of gas formation.
Rocks found in Greenland are up to 3.8 billion years and have bubbles of hydrogen and methane inside them. It is believed that at that time the mechanisms of the subductioncapable of promoting the formation of hydrogen. It is also hypothesized that this gas, rising through the fractures of the rocks, could have reached depths characterized by temperatures compatible with life (not exceeding 122 °C). Here it would have constituted, together with methane, a source of energy for microorganismsof which the first evidence also dates back to around 3.8 billion years ago. Life could therefore have developed first deep in the Earth’s crust and only later moved to the surface. A testimony of how these gases favor life is represented by hydrothermal vents present at the oceanic ridges, particular structures from which water comes out heated by the underlying magma and where primordial microbial communities abound, associated with mantle rocks that have undergone serpentinization.
The Deep Carbon Lab’s studies also have implications in search for microbial life on other planets: here too, in fact, the serpentinization process would be involved. Furthermore, all the information collected on white hydrogen is fundamental to understanding what its role could be in the future clean energy source.
