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Potential precursors of the first building blocks of life observed in deep ocean rocks

The origin of life on Earth is an extremely complex field of research in which several hypotheses have been put forward. Some studies consider extraterrestrial contributions, via meteorites or asteroids, as a source of organic molecules necessary for the seeding of the Earth. Others believe that our planet has, and had, the potential to produce prebiotic chemistry that was sufficiently efficient to generate the first building blocks of life.

Potential precursors of the first building blocks of life observed in deep ocean rocks

Publication date: 07/11/2018

Press, Research

Related themes : Origins

In a study published in the journal Nature, researchers from the Institut de Physique du Globe de Paris, the Université Paris Diderot, the CNRS and the SOLEIL synchrotron provide a first-rate argument for the latter hypothesis, and in particular for the hydrothermal theory of the origin of life, even pushing back its possible emergence to depths well beyond the hydrothermal springs on the ocean floor.

The living world is characterised by its capacity for autonomy and reproduction, but above all by the great complexity of its organic structures. Understanding the transition from a mineral world to increasingly complex organic molecules capable of assembling to create the first building blocks of life is therefore essential to understanding the appearance of life as we know it on Earth.

UV autofluorescence collected on the DISCO light line of the SOLEIL synchrotron, revealing the presence in a clay of an amino acid, tryptophan, formed abiotically during the weathering of the oceanic crust (© IPGP)

In the 1950s, laboratory experiments by two American researchers, Stanley Miller and Harold Urey, showed that the extreme conditions prevailing on the very young Earth could have made it possible for such molecules to be synthesised in the primitive atmosphere before being disseminated in the shallow oceans, even before any form of life appeared. However, this so-called primitive soup hypothesis has never been demonstrated in a natural environment, and the conditions used in these experiments did not reflect those that probably prevailed when life first appeared on Earth.

Optical microscopy photo of a thin section of rock in which abiotic tryptophan (amino acid) was detected. The rock is composed of iron-rich serpentine and saponite (yellow-brown in the photo) disseminated in a network of magnetite (black). (© IPGP)

In a study published on 7 November 2018 in the journal Nature, a team of European scientists, led by Bénédicte Ménez and Céline Pisapia, geomicrobiologists at the Institut de Physique du Globe de Paris (IPGP/Université Paris Diderot/CNRS) and teacher-researchers at the Université Paris Diderot and made up of researchers from the Geology Laboratory of Lyon (Université Claude Bernard/ENS Lyon/CNRS), the French synchrotron radiation centre SOLEIL, the Institut de Chimie des Substances Naturelles (CNRS), and Nazarbayev University in Kazakhstan, used an innovative correlative microscopy approach, combining several high-resolution imaging techniques, on samples taken by drilling about 175 m deep into the oceanic lithosphere during Expedition 304 of the International Ocean Drilling Programme IODP (www.iodp.org).

Using this method, scientists were able to observe amino acids, complex molecules essential to life, synthesised abiotically during the weathering of deep ocean rocks from the Atlantis Massif (Mid-Atlantic Ridge, 30°N).

It was the interaction between seawater and the minerals in these rocks, derived from the Earth’s mantle, and the sheet-like structure of the clay resulting from their alteration, that undoubtedly provided the ideal conditions for the formation of these primary constituents of the first building blocks of life, like a ‘geological mirror’ to Miller’s atmospheric experiments. This observation provides the first clear indication that such a process can occur in terrestrial rocks in conditions close to those that prevailed on the primitive Earth.

This discovery also makes it possible to propose a new synthesis pathway leading to the formation of various molecules of prebiotic interest on the primitive Earth or other planets. This innovative approach and these essential results also provide new avenues for future research in the fields of geobiology and astrobiology, as well as for all disciplines linked to the field of renewable energies and ‘geo-inspired’ chemical and industrial processes.

Ref: B. Ménez, C. Pisapia, M. Andreani, F. Jamme, Q.P. Vanbellingen, A. Brunelle, L. Richard, P. Dumas, M. Réfrégiers. Abiotic synthesis of amino acids in the recesses of the oceanic lithosphere. Nature, doi:10.1038/s41586-018-0684-z

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