Design and Construction of an Experimental Setup to Enhance Mineral Weathering through the Activity of Soil Organisms

Enhanced weathering (EW) is an emerging carbon dioxide (CO2) removal technology that can contribute to climate change mitigation. This technology relies ...

Uppsala University

Rock⁻water⁻carbon interactions germane to serpentinization in hydrothermal vents have occurred for over 4 billion years, ever since there was liquid water on Earth. Serpentinization converts iron(II) containing minerals and water to magnetite (Fe₃O₄) plus H₂. The hydrogen can generate native metals such as awaruite (Ni₃Fe), a common serpentinization product. Awaruite catalyzes the synthesis of methane from H₂ and CO₂ under hydrothermal conditions. Native iron and nickel catalyze the synthesis of formate, methanol, acetate, and pyruvate-intermediates of the acetyl-CoA pathway, the most ancient pathway of CO₂ fixation. Carbon monoxide dehydrogenase (CODH) is central to the pathway and employs Ni⁰ in its catalytic mechanism. CODH has been conserved during 4 billion years of evolution as a relic of the natural CO₂-reducing catalyst at the onset of biochemistry. The carbide-containing active site of nitrogenase-the only enzyme on Earth that reduces N₂-is probably also a relic, a biological reconstruction of the naturally occurring inorganic catalyst that generated primordial organic nitrogen. Serpentinization generates Fe₃O₄ and H₂, the catalyst and reductant for industrial CO₂ hydrogenation and for N₂ reduction via the Haber⁻Bosch process. In both industrial processes, an Fe₃O₄ catalyst is matured via H₂-dependent reduction to generate Fe₅C₂ and Fe₂N respectively. Whether serpentinization entails similar catalyst maturation is not known. We suggest that at the onset of life, essential reactions leading to reduced carbon and reduced nitrogen occurred with catalysts that were synthesized during the serpentinization process, connecting the chemistry of life and Earth to industrial chemistry in unexpected ways.

Serpentinization: Connecting Geochemistry, Ancient Metabolism and Industrial Hydrogenation.

The first organisms on the young Earth, just 1-1.5 billion years old, were likely chemolithoautotrophic anaerobes, thriving in an anoxic world rich in water, CO, and N. It is generally assumed that, until the accumulation of O in the atmosphere, life was exempted from the oxidative stress that reactive oxygen species (ROS) impose on hydrocarbon-based life. Therefore, it is perplexing to note that life on the early Earth already carried antioxidants such as superoxide dismutase enzymes, catalase, and peroxiredoxins, the function of which is to counteract all forms of ROS, including HO. Phylogenetic investigations suggest that the presence of these enzymes in the last universal common ancestor, far predating the great oxygenation event (GOE) sometime between 2.3 and 2.7 billion years ago, is thought to be due to the appearance of oxygen-producing microorganisms and the subsequent need to respond to the appearance of ROS. Since the metabolic enzymes that counteract ROS have been found in all domains of life, they are considered of primitive origin. Two questions arise: (1) Could there be a nonbiological source of ROS that predates the oxygenic microbial activity? (2) Could sulfur, the homologue of oxygen, have played that role? Reactive sulfur species (RSS) may have triggered the evolution of antioxidants such that the ROS antioxidants started out as "antisulfur" enzymes developed to cope with, and take advantage of, various forms of RSS that were abundantly present on the early Earth.

Sulfur Chemistry May Have Paved the Way for Evolution of Antioxidants.

Accurate isotope ratio measurements are of high importance in various scientific fields, ranging from radio isotope geochronology of solids to studies of element isotopes fractionated by living organisms. Instrument limitations, such as unresolved isobaric inferences in the mass spectra, or cosampling of the material of interest together with the matrix material may reduce the quality of isotope measurements. Here, we describe a method for accurate isotope ratio measurements using our laser ablation ionization time-of-flight mass spectrometer (LIMS) that is designed for in situ planetary research. The method is based on chemical depth profiling that allows for identifying micrometer scale inclusions embedded in surrounding rocks with different composition inside the bulk of the sample. The data used for precise isotope measurements are improved using a spectrum cleaning procedure that ensures removal of low quality spectra. Furthermore, correlation of isotopes of an element is used to identify and reject the data points that, for example, do not belong to the species of interest. The measurements were conducted using IR femtosecond laser irradiation focused on the sample surface to a spot size of ~12 μm. Material removal was conducted for a predefined number of laser shots, and time-of-flight mass spectra were recorded for each of the ablated layers. Measurements were conducted on NIST SRM 986 Ni isotope standard, trevorite mineral, and micrometer-sized inclusions embedded in aragonite. Our measurements demonstrate that element isotope ratios can be measured with accuracies and precision at the permille level, exemplified by the analysis of B, Mg, and Ni element isotopes. The method applied will be used for in situ investigation of samples on planetary surfaces, for accurate quantification of element fractionation induced by, for example, past or present life or by geochemical processes.

Isotope abundance ratio measurements using femtosecond laser ablation ionization mass spectrometry.

In this contribution, we present results of non-linear dimensionality reduction and classification of the fs laser ablation ionization mass spectrometry (LIMS) imaging dataset acquired from the Precambrian Gunflint chert (1.88 Ga) using a miniature time-of-flight mass spectrometer developed for  space applications. We discuss the data generation, processing, and analysis pipeline for the classification of the recorded fs-LIMS mass spectra. Further, we define topological biosignatures identified for Precambrian Gunflint microfossils by projecting the recorded fs-LIMS intensity space into low dimensions. Two distinct subtypes of microfossil-related spectra, a layer of organic contamination and inorganic quartz matrix were identified using the fs-LIMS data. The topological analysis applied to the fs-LIMS data allows to gain additional knowledge from large datasets, formulate hypotheses and quickly generate insights from spectral data. Our contribution illustrates the utility of applying spatially resolved mass spectrometry in combination with topology-based analytics in detecting signatures of early (primitive) life. Our results indicate that fs-LIMS, in combination with topological methods, provides a powerful analytical framework and could be applied to the study of other complex mineralogical samples.

On Topological Analysis of fs-LIMS Data. Implications for in Situ Planetary Mass Spectrometry.

A number of negative emission technologies (NETs) have been proposed to actively remove CO from the atmosphere, with enhanced silicate weathering (ESW) as a relatively new NET with considerable climate change mitigation potential. Models calibrated to ESW rates in lab experiments estimate the global potential for inorganic carbon sequestration by ESW at about 0.5-5 Gt CO  year , suggesting ESW could be an important component of the future NETs mix. In real soils, however, weathering rates may differ strongly from lab conditions. Research on natural weathering has shown that biota such as plants, microbes, and macro-invertebrates can strongly affect weathering rates, but biotic effects were excluded from most ESW lab assessments. Moreover, ESW may alter soil organic carbon sequestration and greenhouse gas emissions by influencing physicochemical and biological processes, which holds the potential to perpetuate even larger negative emissions. Here, we argue that it is likely that the climate change mitigation effect of ESW will be governed by biological processes, emphasizing the need to put these processes on the agenda of this emerging research field.

Is the climate change mitigation effect of enhanced silicate weathering governed by biological processes?

The investigation of chemical composition on planetary bodies without significant sample processing is of importance for nearly every mission aimed at robotic exploration. Moreover, it is a necessary tool to achieve the longstanding goal of finding evidence of life beyond Earth, for example, possibly preserved microbial remains within martian sediments. Our Laser Ablation Ionization Mass Spectrometer (LIMS) is a compact time-of-flight mass spectrometer intended to investigate the elemental, isotope, and molecular composition of a wide range of solid samples, including e.g., low bulk density organic remains in microfossils. Here, we present an overview of the instrument and collected chemical spectrometric data at the micrometer level from a Precambrian chert sample (1.88 Ga Gunflint Formation, Ontario, Canada), which is considered to be a martian analogue. Data were collected from two distinct zones-a silicified host area and a carbon-bearing microfossil assemblage zone. We performed these measurements using an ultrafast pulsed laser system (pulse width of ∼180 fs) with multiple wavelengths (infrared [IR]-775 nm, ultraviolet [UV]-387 nm, UV-258 nm) and using a pulsed high voltage on the mass spectrometer to reveal small organic signals. We investigated (1) the chemical composition of the sample and (2) the different laser wavelengths' performance to provide chemical depth profiles in silicified media. Our key findings are as follows: (1) microfossils from the Gunflint chert reveal a distinct chemical composition compared with the host mineralogy (we report the identification of 24 elements in the microfossils); (2) detection of the pristine composition of microfossils and co-occurring fine chemistry (rare earth elements) requires utilization of the depth profiling measurement protocol; and (3) our results show that, for analysis of heterogeneous material from siliciclastic deposits, siliceous sinters, and cherts, the most suitable wavelength for laser ablation/Ionization is UV-258 nm.

Multiwavelength Ablation/Ionization and Mass Spectrometric Analysis of 1.88 Ga Gunflint Chert.

Organic molecules preserved in fossils provide a wealth of new information about ancient life. The discovery of almost unaltered complex organic molecules in well-preserved fossils raise the question of how common such occurrences are in the fossil record, how to differentiate between endogenous and exogenous sources for the organic matter and what promotes such preservation. The aim of this study was the in-situ analysis of a well-preserved vertebrate fossil from 48 Ma Eocene sediments in the Messel pit, Germany for preservation of complex biomolecules. The fossil was characterized using a variety of techniques including time-of-flight secondary ion mass spectrometry (ToF-SIMS), scanning electron microscopy/energy dispersive x-ray spectroscopy (SEM/EDX), x-ray diffraction (XRD) and Raman spectroscopy. A suite of organic molecules was detected, including porphyrins, which given the context of the detected signal are most probably diagenetically altered heme originating from the fossil though a microbial contribution cannot be completely ruled out. Diagenetic changes to the porphyrin structure were observed that included the exchange of the central iron by nickel. Further analyses on the geochemistry of the fossil and surrounding sediments showed presence of pyrite and aluminosilicates, most likely clay. In addition, a carbonate and calcium phosphate dominated crust has formed around the fossil. This suggests that several different processes are involved in the preservation of the fossil and the organic molecules associated with it. Similar processes seem to have also been involved in preservation of heme in fossils from other localities.

Detection of porphyrins in vertebrate fossils from the Messel and implications for organic preservation in the fossil record.

Manganese (Mn) oxides are ubiquitous in nature and occur as both biological and abiotic minerals, but empirically distinguishing between the two remains a problem. Recently, electron paramagnetic resonance (EPR) spectroscopy has been proposed for this purpose. It has been reported that biogenic Mn oxides display a characteristic narrow linewidth in contrast to their pure abiotic counterparts, which is explained in part by the large number of cation vacancies that form within the layers of biogenic Mn oxides. It was, therefore, proposed that natural samples that display a narrow EPR linewidth, Δ < 580G, could be assigned to a biogenic origin. However, in poorly crystalline or amorphous solids, both dipolar broadening and exchange narrowing simultaneously determine the linewidth. Considering that the spectral linewidth is governed by several mechanisms, this approach might be questioned. In this study, we report synthetic chemical garden Mn oxide biomorphs that exhibit both morphologically life-like structures and narrow EPR linewidths, suggesting that a narrow EPR line may be unsuitable as reliable evidence in assessment of biogenicity.

Anna Neubeck

Department of Earth Sciences

Uppsala University

Design and Construction of an Experimental Setup to Enhance Mineral Weathering through the Activity of Soil Organisms

Anna Neubeck

.css-o250i3{font-size:18px;font-family:Open Sans,sans-serif;line-height:21.6px;}Department of Earth Sciences

Uppsala University

Design and Construction of an Experimental Setup to Enhance Mineral Weathering through the Activity of Soil Organisms

Department of Earth Sciences