Prebiotic Chemistry

The study of Prebiotic Chemistry, and the closely related study of Astrobiology, is ultimately the study of our own point(s) of origin. Aiming to answer the questions of how, when, and where did the building blocks of life—i.e. biologically relevant organic molecules—form? With the imminent analysis of samples successfully returned from the near-Earth asteroid Bennu, and continuing discoveries from the Ryugu asteroid samples, the answers to some of these questions may be in sight.

The early Hadean eon (>4Ga) may have had a periodically ice-covered global ocean and limited subaerial landmass, and this could have resulted in infrequent lightning occurrence. This infrequency of lightning may have limited the synthesis of prebiotic compounds necessary for life’s origins. Here I present a hypothesis that lightning associated with volcanic island eruptions created focal points for the generation of prebiotic ingredients and ultimately the origin of life.

The samples returned from near-Earth asteroid (162173) Ryugu provide a pristine record of the 4.6 billion years since the birth of the Solar System. The Hayabusa2 initial analysis team has integrated a range of analytical techniques to investigate Ryugu’s organic chemistry. Here, we highlight their latest findings, the potential questions which may be answered, and provide an overview of new prospects in the decade to come.

Though the lunar samples returned by the Apollo and Luna missions have been studied for more than 50 years, scientists are discovering new clues into the early evolution of the Moon by looking through the lens of modern analytical techniques.

How complex organics form in a prebiotic world remains a missing key to establish where life emerged. The authors present a road to abiotic organic synthesis and diversification in hydrothermal contexts involving magmatism and rock hydration.

Phosphate is critical for all life on Earth but its origins have remained enigmatic. Experiments indicate that phosphate may have been abundant in ancient Fe-rich seawater, providing a crucial ingredient for the origins of life on Earth.

Researchers at Newcastle University have discovered a mechanism by which earthquakes create bursts of hydrogen peroxide and oxygen in hot underground fractures. These may have played a vital role in the early evolution and origin of life on Earth.

Hydrogen peroxide (H₂O₂) has been proposed as an electron donor for photosynthesis before water, however, the amount of H₂O₂ available on early Earth was thought to be limited. Here the authors propose a new abiotic pathway wherein abrasion of quartz surfaces would have provided enough H₂O₂.

Using diamond anvil cell and high temperature experiments, this work proves that the interaction between deep hydrogen rich fluids and reduced carbon minerals may be an efficient mechanism for producing abiotic hydrocarbons at the upper mantle’s pressures and temperatures.

Iron-sulfur (FeS) proteins are involved in electron transfer and CO₂ fixation. Here, the authors show that FeS clusters can form spontaneously in the presence of the amino acid cysteine, in conditions similar those expected in Hadean alkaline hydrothermal vents, suggesting a plausible mechanism of their emergence at the origin of life.

Determining the origins of life on Earth is confounded by the fact that the sources of nutrients necessary to create early life forms remain mysterious. Here the authors show that lightning strikes could have supplied a major source of essential phosphorus on early Earth.

It is widely hypothesised that primeval life utilized small organic molecules as sources of carbon and energy, however, the presence of such primordial ingredients in early Earth habitats has not yet been demonstrated. Here the authors report the existence of indigenous organic molecules and gases in primary fluid inclusions in c. 3.5- billion-year-old rocks from Western Australia.

Abiotic methane and ethane formation routes in aqueous environments driven by light and heat are identified. The released hydrocarbons may have contributed to the chemical evolution of the atmosphere from prior to the origin of life until today.

A deep, ancient, and uranium-rich brine in South Africa reveals evidence of radiolytically oxidized kerogen and C₁–C₃ hydrocarbons with abiotic isotopic signatures that support a low biomass microbial community over time.

Mars has long been thought to contain organic compounds, but the origins and plausibility are debated. Here the authors employ a new technique to assess organic nitrogen compounds in a Martian meteorite, concluding that these compounds are indeed likely to originate from the Red Planet.

Excess of l-amino acids in meteorites suggests an extraterrestrial origin of biomolecular homochirality, which may stem from chiral light-matter interactions. Here the authors support this hypothesis with asymmetric photolysis experiments on racemic isovaline films, showing that circularly polarized starlight can produce l-enantiomeric excesses that can be amplified during parent bodies’ alteration.

This manuscript tackles the origin of organic molecules in carbonaceous meteorites. Identifying hexamethylenetetramine in three carbonaceous meteorites, the authors propose formation from ammonia and formaldehyde by photochemical and thermal reactions in the interstellar medium, followed by the incorporation into planetary systems.

Researchers at Earth-Life Science Institute (ELSI) discovered a chemical process that can explain the very low amino acid abundances in aqueously altered carbonaceous chondrites, deepening our understanding on the Solar System chemical evolution.

All DNA/RNA nucleobases were identified in carbonaceous meteorites. Having been provided to the early Earth as a component in carbonaceous meteorites, these molecules might have played a role for the emergence of genetic functions in early life.

Cyanide is thought to be crucial for the origin of life. Here, the authors showed that iron cyanocarbonyl complexes are present in meteorites and propose that these compounds were a source of free cyanide on early Earth and served as precursors to the active sites of ancient hydrogenases.

Uracil was identified in the sample returned from the asteroid Ryugu. Having been provided to the early Earth as a component in such asteroidal materials, these molecules might have played a role for prebiotic chemical evolution on the early Earth

Amino acid concentrations from 2 particles returned from different touchdown sites on the surface of Ryugu are reported. Differences in chemistry suggest different levels of aqueous alteration are recorded at the 2 sampled locations.

The asteroid Ryugu samples are by far the freshest extraterrestrial carbonaceous material. The authors report soluble ions and organic sulfur molecules linked with primordial brine and prebiotic organic evolution of the primitive asteroid.

The authors report the discovery of salts and fresh organic-rich exposures in the Urvara basin, possibly linked to a late resurfacing of the crater floor. These results are consistent with a deep-seated brine/salt reservoir in the crust of Ceres.

A new analysis of Rosetta mass spectra reveals an ensemble of complex organic molecules with striking similarities to other organic reservoirs in the Solar System, including Saturn’s ring rain material, pointing at a likely joint prestellar history.

Is phosphorous a limiting factor for life on ocean worlds (e.g. Europa and Enceladus)? Calculated dissolved phosphate concentrations from a wide range of possible water-rock reactions suggest cell populations larger than those observed in Earth’s deep oceans could be supported.

The metabolisms proposed for hypothetical life in the clouds of Venus cannot explain the planet’s atmospheric chemistry and thus a limit can be placed on the maximum allowed biomass.

The search for life in the universe is difficult due to issues with defining signatures of living systems. Here, the authors present an approach based on the molecular assembly number and tandem mass spectrometry that allows identification of molecules produced by biological systems, and use it to identify biosignatures from a range of samples, including ones from outer space.