Earth: Atmospheric Evolution of a Habitable Planet

Our present-day atmosphere is often used as an analog for potentially habitable exoplanets, but Earth's atmosphere has changed dramatically throughout its 4.5 billion year history. For example, molecular oxygen is abundant in the atmosphere today but was absent on the early Earth. Meanwhile, the physical and chemical evolution of Earth's atmosphere has also resulted in major swings in surface temperature, at times resulting in extreme glaciation or warm greenhouse climates. Despite this dynamic and occasionally dramatic history, the Earth has been persistently habitable--and, in fact, inhabited--for roughly 4 billion years. Understanding Earth's momentous changes and its enduring habitability is essential as a guide to the diversity of habitable planetary environments that may exist beyond our solar system and for ultimately recognizing spectroscopic fingerprints of life elsewhere in the Universe. Here, we review long-term trends in the composition of Earth's atmosphere as it relates to both planetary habitability and inhabitation. We focus on gases that may serve as habitability markers (CO2, N2) or biosignatures (CH4, O2), especially as related to the redox evolution of the atmosphere and the coupled evolution of Earth's climate system. We emphasize that in the search for Earth-like planets we must be mindful that the example provided by the modern atmosphere merely represents a single snapshot of Earth's long-term evolution. In exploring the many former states of our own planet, we emphasize Earth's atmospheric evolution during the Archean, Proterozoic, and Phanerozoic eons, but we conclude with a brief discussion of potential atmospheric trajectories into the distant future, many millions to billions of years from now. All of these 'Alternative Earth' scenarios provide insight to the potential diversity of Earth-like, habitable, and inhabited worlds.Comment: 34 pages, 4 figures, 4 tables. Review chapter to appear in Handbook of Exoplanet

Globally asynchronous sulphur isotope signals require re-definition of the Great Oxidation Event

© 2018 The Author(s). The Great Oxidation Event (GOE) has been defined as the time interval when sufficient atmospheric oxygen accumulated to prevent the generation and preservation of mass-independent fractionation of sulphur isotopes (MIF-S) in sedimentary rocks. Existing correlations suggest that the GOE was rapid and globally synchronous. Here we apply sulphur isotope analysis of diagenetic sulphides combined with U-Pb and Re-Os geochronology to document the sulphur cycle evolution in Western Australia spanning the GOE. Our data indicate that, from ~2.45 Gyr to beyond 2.31 Gyr, MIF-S was preserved in sulphides punctuated by several episodes of MIF-S disappearance. These results establish the MIF-S record as asynchronous between South Africa, North America and Australia, argue for regional-scale modulation of MIF-S memory effects due to oxidative weathering after the onset of the GOE, and suggest that the current paradigm of placing the GOE at 2.33-2.32 Ga based on the last occurrence of MIF-S in South Africa should be re-evaluated

Divergence in self- and peer-reported victimization and its association to concurrent and prospective adjustment

Item does not contain fulltextPrevious studies on victimization have either used self-reports of peer-reports, but correspondence between these measures is low, implying that types of victims may exist that differ in convergence between self- and peer-reported victimization. Importantly, the very few studies that do exist on such types were cross-sectional, and did not address the stability nor predictive validity in terms of adjustment of these types. Using a person-centered approach, the present study identified types of victims that were either convergent or divergent in self- and peer-reported victimization, and examined how these types differed in concurrent and prospective adjustment. Participants were 1,346 adolescents (50 % girls, mean age 14.2) who were followed for 1 year. Using Latent Profile Analysis, we identified two convergent types (self-peer identified victims and non-victims) and two divergent types (self-identified and peer-identified) of victims. The types were highly stable over time. Self-peer identified victims were not only concurrently but also prospectively the least well adjusted. Self-identified victims showed lower levels of emotional adjustment but did not show problems on social adjustment. On the other hand, peer-identified victims were at risk for social but not emotional maladjustment. The findings corroborate previous studies that suggest that self-reported victimization is related to emotional problems, while peer-reported victimization is more indicative of social problems. The findings also suggest that using self-reports or peer-reports only may lead to incomplete conclusions about victims' adjustment on different domains.22 p