The Role of N2 as a Geo-Biosignature for the Detection and Characterization of Earth-like Habitats

Since the Archean, N2 has been a major atmospheric constituent in Earth's atmosphere. Nitrogen is an essential element in the building blocks of life, therefore the geobiological nitrogen cycle is a fundamental factor in the long term evolution of both Earth and Earth-like exoplanets. We discuss the development of the Earth's N2 atmosphere since the planet's formation and its relation with the geobiological cycle. Then we suggest atmospheric evolution scenarios and their possible interaction with life forms: firstly, for a stagnant-lid anoxic world, secondly for a tectonically active anoxic world, and thirdly for an oxidized tectonically active world. Furthermore, we discuss a possible demise of present Earth's biosphere and its effects on the atmosphere. Since life forms are the most efficient means for recycling deposited nitrogen back into the atmosphere nowadays, they sustain its surface partial pressure at high levels. Also, the simultaneous presence of significant N2 and O2 is chemically incompatible in an atmosphere over geological timescales. Thus, we argue that an N2-dominated atmosphere in combination with O2 on Earth-like planets within circumstellar habitable zones can be considered as a geo-biosignature. Terrestrial planets with such atmospheres will have an operating tectonic regime connected with an aerobe biosphere, whereas other scenarios in most cases end up with a CO2-dominated atmosphere. We conclude with implications for the search for life on Earth-like exoplanets inside the habitable zones of M to K-stars

Ariel – a window to the origin of life on early earth?

Is there life beyond Earth? An ideal research program would first ascertain how life on Earth began and then use this as a blueprint for its existence elsewhere. But the origin of life on Earth is still not understood, what then could be the way forward? Upcoming observations of terrestrial exoplanets provide a unique opportunity for answering this fundamental question through the study of other planetary systems. If we are able to see how physical and chemical environments similar to the early Earth evolve we open a window into our own Hadean eon, despite all information from this time being long lost from our planet’s geological record. A careful investigation of the chemistry expected on young exoplanets is therefore necessary, and the preparation of reference materials for spectroscopic observations is of paramount importance. In particular, the deduction of chemical markers identifying specific processes and features in exoplanetary environments, ideally “uniquely”. For instance, prebiotic feedstock molecules, in the form of aerosols and vapours, could be observed in transmission spectra in the near future whilst their surface deposits could be observed from reflectance spectra. The same detection methods also promise to identify particular intermediates of chemical and physical processes known to be prebiotically plausible. Is Ariel truly able to open a window to the past and answer questions concerning the origin of life on our planet and the universe? In this paper, we discuss aspects of prebiotic chemistry that will help in formulating future observational and data interpretation strategies for the Ariel mission. This paper is intended to open a discussion and motivate future detailed laboratory studies of prebiotic processes on young exoplanets and their chemical signatures

Development of the Earth's Nitrogen Atmosphere in the Archean and During the Great Oxidation Event Transition

Stickstoff ist, in der Form von N2, der größte Bestandteil der heutigen Erdatmosphäre. Allein schon diese Eigenschaft ist auf keinem anderen der terrestrischen Planeten zu finden, allerdings ist die Kombination mit O2 als zweitgrößten Bestandteil sogar im gesamten Sonnensysten einmalig. Die Voraussetzungen für das Entstehen der dauerhaft stabilen N2-O2-Atmosphäre auf der Erde sind weitgehend unbekannt, genauso wie die Prozesse, die zu ihrem Aufbau geführt haben. Interaktionen zwischen der Geochemie der frühen Erde, ihrer inneren thermischen Entwicklung und ihrer Tektonik, der Entwicklung der frühen Sonne und dem wachsenden Einfluss des Lebens scheinen zu diesen Bediungen geführt zu haben. Dieses Zusammenspiel ist Objekt aktueller Forschung.Die N2-O2-Atmosphäre ist eine entscheidende Eigenschaft des Lebensraums auf der Erde. Das enge Zusammenwirken von Lebensformen und atmosphärischem Stickstoff ist gut erforscht; dieser Stickstoff ist Ausgangspunkt der Versorgung für Nährstoffe und kann damit biologische Aktitivtäten regulieren. In Aminosäuren, den Grundbausteinen allen bekannten Lebens, ist die namengebende Aminogruppe ein wichtiger funktioneller Part. Daraus ergibt sich, dass die Verfügbarkeit von Stickstoff die Habitabilität eines Planeten mitdefiniert. Obwohl viel Forschung betrieben wurde, sind die Rolle und die Synthese von Stickstoff-basierten Verbindungen während der Entwicklung der ersten Lebensformen nur zu kleinen Teilen bekannt.In der hier präsentierten Arbeit werden die geobiologischen Stickstoffkreisläufe der frühen und der heutigen Erde ausgearbeitet und verglichen. Das Ziel ist die Bewertung möglicher Szenarios für die frühe Entwicklung von atmosphärischem Stickstoff beginnend in der Zeit der zweiten Hälfte des Hadaikums (vor 4350 Millionen Jahren), über das Archaikum bis kurz nach der großen Sauerstoffkatastrophe (bis vor 2000 Millionen Jahren). Um realistische Entwicklungsscenarien für den Aufbau von N2 auf der frühen Erde auszuarbeiten wird die Effizienz diverser Prozesse des oberen und tiefen Stickstoffkreislaufs untersucht. Im weiteren Verlauf der Arbeit wird ein Computermodell, genannt Nitrogen Development (NDEV) Modell, entwickelt, um Aussagen über die Entwicklung der N2 Menge in der Atmosphäre unter zuvor diskutierten Voraussetzungen und Randbedingungen treffen zu können.Ein Resultat ist der Hinweis auf das Fehlen einer effizienten Quelle für atmoshärischen Stickstoff im momentanen Verständnis des Stickstoffkreislaufs der frühen Erde, oder aber es gab eine Zeit des schwächeren Abbaus im späteren Archaikum. Außerdem wird gezeigt, dass das hier entwickelte Modell im Einklang mit verschiedenen geologischen Studien ist, während andere, frühere Modelle teils deutlich davon abweichen. Für den Zeitraum des frühen Archaikums wurden N2-Drücke errechnet, die 150mbar nicht überschreiten. Aus aeronomischer Sicht, fußend auf die Untersuchung von Stickstoffisotopen, ist eine N2-dominierte Atmosphäre auf der frühen Erde nicht möglich gewesen, was mit den hier präsentierten Modellrechnungen übereinstimmt. Im Allgemeinen war der Stickstoff Partialdruck über die Erdgeschichte wohl nicht stabil.Nitrogen in the form of N2 constitutes the main bulk gas in the present Earths atmosphere. While such a N2-dominated atmosphere is unique on the terrestrial planets, its combination with O2 as second bulk gas is exceptional in the entire solar system. The requirements for the emergence of the Earths long-term stable N2-O2 atmosphere are still widely unknown, as are the processes that led to its buildup. An interplay of the early Earths geochemistry, its thermal evolution and tectonic regime, the evolution of the early Sun, and the growing influence of a biosphere seem to have led to these conditions, which is object of current research.The N2-O2-dominated atmosphere is a crucial feature of the Earths habitat. It is well-known that lifeforms interact closely with atmospheric nitrogen; the nitrogen partial pressure can pro-vide or limit nutrients and therefore biological productivity. In amino acids, the building blocks of all known lifeforms, the nitrogen containing amino groups are an important functional part and also their eponymous component. Therefore, the availability of nitrogen in its various forms can enable or prevent a planets habitability. Although it is part of intensive research, the role and formation of nitrogen-containing compounds during the emergence of the first lifeforms is also not clarified yet.In the present work, the modern and early forms of the geobiological nitrogen cycle are investigated and compared. The main aim is the evaluation of possible scenarios for the early evolution of the atmospheric nitrogen amount throughout the late Hadean and the Archean, as well as during the Great Oxidation Event transition (4350 to 2000 Myr ago). In order to work out realistic scenarios for the early Earths atmospheric N2, the efficiencies of diverse processes which are affecting nitrogen in the upper part and in the deep part of the geobiological nitrogen cycle are examined. In the further course of this work, a model approach, named nitrogen development (NDEV) model, is performed to provide estimates of the N2 development under the previously discussed conditions and constraints.It is found that the current understanding of the early nitrogen cycle either misses an efficient outgassing/regassing process, or its depletion processes must have had a time of unefficiency during the late Archean. Further, it is shown that the here presented model is roughly in agreement with geological constraints, while other models shows wide deviations. For the early Archean, rather low N2 partial pressures not exceeding 150 mbar were found. From an aeronomical perspective, nitrogen isotopic ratios also show that a long-term N2-dominated atmosphere on early Earth has not been present, which is corresponding to the NDEV model results. In general, the atmospheric nitrogen amount was most likely not stable throughout the early Earths history.Arbeit an der Bibliothek noch nicht eingelangt - Daten nicht geprüftAbweichender Titel laut Übersetzung des Verfassers/der VerfasserinKarl-Franzens-Universität Graz, Masterarbeit, 2019(VLID)438354

Future Missions related to the determination of the elemental and isotopic composition of Earth, Moon and the terrestrial planets

International audienceIn this chapter we review the contribution of space missions to the determination of the elemental and isotopic composition of Earth, Moon and the terrestrial planets, with special emphasis on currently planned and future missions. We show how these missions are going to significantly contribute to, or sometimes revolutionise, our understanding of planetary evolution, from formation to the possible emergence of life. We start with the Earth, which is a unique habitable body with actual life, and that is strongly related to its atmosphere. The new wave of missions to the Moon is then reviewed, which are going to study its formation history, the structure and dynamics of its tenuous exosphere and the interaction of the Moon’s surface and exosphere with the different sources of plasma and radiation of its environment, including the solar wind and the escaping Earth’s upper atmosphere. Missions to study the noble gas atmospheres of the terrestrial planets, Venus and Mars, are then examined. These missions are expected to trace the evolutionary paths of these two noble gas atmospheres, with a special emphasis on understanding the effect of atmospheric escape on the fate of water. Future missions to these planets will be key to help us establishing a comparative view of the evolution of climates and habitability at Earth, Venus and Mars, one of the most important and challenging open questions of planetary science. Finally, as the detection and characterisation of exoplanets is currently revolutionising the scope of planetary science, we review the missions aiming to characterise the internal structure and the atmospheres of these exoplanets