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The habitability of Earth significantly depends on the evolution of its atmospheric properties, which are strongly influenced by escape processes. Polar outflow, which encompasses the atmospheric escape of ions through the open field lines of the Earth's magnetosphere, is the dominant escape process for modern Earth and likely played a significant role in Earth's early history as well. In this article, we investigate the evolution of Earth's polar outflow during the Archean eon 3-4 gigayears (Ga) ago for an N 2 -CO 2 atmosphere. For this, we use a kinetic direct simulation Monte Carlo (DSMC) particle code to simulate the interactions between the solar wind and the Earth's upper atmosphere. We explore the effects of different CO 2 mixing ratios (10%, 25%, 50%, 75%, 99%) on the polar outflow escape rates of oxygen, nitrogen and carbon. Using the ion production rates as an estimate for polar outflow, our results indicate that during the time 3.6-4.0 Ga ago, a CO 2 mixing ratio larger than 25% may have been necessary to avoid excessive escape via polar outflow. Close to 4 Ga ago, even 50% CO 2 may have been necessary due to the stronger solar winds. Our results align with other studies also suggesting a similarly high CO 2 mixing ratio in the early Archean. • Polar outflow is a non-negligible atmospheric escape process for magnetized planets • Early Archean Earth may have had 25%-50% CO 2 to prevent excessive polar outflow • Studies on thermal and non-thermal escape suggest similar levels of necessary CO 2 [ABSTRACT FROM AUTHOR]

• Earth Archean upper atmosphere studied using state-of-the-art models. • High atmospheric CO 2 levels and low solar activity needed to prevent rapid escape to space. • At least 40% of atmospheric gas was CO 2 at 3.8 billion year ago. • Greenhouse effect from CO 2 was strong enough to solve faint young Sun problem. • The Sun must have been born as a slow rotator with low activity. Despite their importance for determining the evolution of the Earth's atmosphere and surface conditions, the evolutionary histories of the Earth's atmospheric CO 2 abundance during the Archean eon and the Sun's activity are poorly constrained. In this study, we apply a state-of-the-art physical model for the upper atmosphere of the Archean Earth to study the effects of different atmospheric CO 2 /N 2 mixing ratios and solar activity levels on the escape of the atmosphere to space. We find that unless CO 2 was a major constituent of the atmosphere during the Archean eon, enhanced heating of the thermosphere by the Sun's strong X-ray and ultraviolet radiation would have caused rapid escape to space. We derive lower limits on the atmospheric CO 2 abundance of approximately 40% at 3.8 billion years ago, which is likely enough to counteract the faint young Sun and keep the Earth from being completely frozen. Furthermore, our results indicate that the Sun was most likely born as a slow to moderate rotating young G-star to prevent rapid escape, putting essential constraints on the Sun's activity evolution throughout the solar system's history. In case that there were yet unknown cooling mechanisms present in the Archean atmosphere, this could reduce our CO 2 stability limits, and it would allow a more active Sun. [ABSTRACT FROM AUTHOR]

Abstract: We present results of an investigation aimed at characterizing the effects of oceanic impacts of 500m and 1km diameter asteroids on the lower and middle atmosphere, estimating ozone loss and potential danger from UV radiation at the Earth''s surface. Little work has been done so far to assess the atmospheric perturbation from the impact of objects in this size range, even though their sizes are close to the threshold for causing global environmental effects. In particular, at the Earth''s surface oceanic impacts are twice more likely to occur than land impacts. This work represents the first attempt at combining impact simulations with a three-dimensional shock physics code (SOVA), and atmospheric simulations using the general circulation model with interactive chemistry WACCM. SOVA simulations provided an estimate of the amount and state of material ejected into the atmosphere by the impacts. Estimated water vapor in the upper atmosphere was then introduced in the initial conditions for the WACCM simulations that modeled the subsequent perturbation of atmospheric chemistry Final estimates of the change over time in UV flux at the surface due to the impact-induced ozone change are then carried out using the TUV radiative transfer model. The results suggest that mid-latitude oceanic impacts of 1km asteroids can produce a significant, global perturbation of upper atmospheric chemistry, including multi-year global ozone depletion comparable to ozone hole records registered in the mid-1990s. Asteroids 500m in diameter cause limited perturbations of upper atmospheric chemistry with significant ozone depletion confined to the hemisphere in which the impact occurred. Impact-induced ozone depletion affects UV irradiance at the Earth''s surface, resulting in levels of UV-B irradiance that can be dangerous for living organisms, and, in the tropics and initial midlatitude summers, far exceed levels currently experienced anywhere on Earth. [Copyright &y& Elsevier]

Abstract: The evolution of the particle background at an altitude of ~540 km during the time interval between 1996 and 2007 is studied using the particle monitor of the High Energy X-ray Timing Experiment on board NASA''s Rossi X-ray Timing Explorer. A special emphasis of this study is the location and strength of the South Atlantic Anomaly (SAA). The size and strength of the SAA are anti-correlated with the 10.7 cm radio flux of the Sun, which leads the SAA strength by ~1 year reflecting variations in solar heating of the upper atmosphere. The location of the SAA is also found to drift westwards with an average drift rate of about 0.3°/yr following the drift of the geomagnetic-field configuration. Superimposed to this drift rate are irregularities, where the SAA suddenly moves eastwards and where furthermore the speed of the drift changes. The most prominent of these irregularities is found in the second quarter of 2003 and another event took place in 1999. We suggest that these events are previously unrecognized manifestations of the geomagnetic jerks of the Earth''s magnetic field. [Copyright &y& Elsevier]

This study explores a chemo-thermo-dynamic subduction zone model that solves for slab dehydration during subduction. We investigate how changes in the incoming plate''s hydration and thermal structure may effect the efficiency of sub-arc water release from sediments, crust, and serpentinized mantle. We find that serpentinized lithospheric mantle may not only be an important fluid source to trigger arc melting but is also an efficient ‘transport-lithology’ to recycle chemically bound water into the deeper mantle. In fact, an old slab may remain sufficiently cold during subduction to retain up to 40% of its initial ‘mantle’ water at 8 GPa (∼240-km depth) after serpentine transforms to higher pressure hydrous phase A.Furthermore, deep water recycling at subduction zones is parameterized in terms of slab age and speed. Coupling this parameterization to a parameterized mantle convection evolution model allows us to calculate the mantle-surface geologic water cycle throughout the Earth''s history. We find that the present-day Earth mantle may be highly outgassed containing only a small fraction of the Earth''s water, which would mostly be recycled water from the exosphere. [Copyright &y& Elsevier]

The oceanic thermocline circulation provides a route of communication between the surface and deep ocean and could have played an important role in the global carbon cycle, but studies on reconstructing past thermocline water properties are limited. Here we explore the potential use of left-coiling Globorotalia truncatulinoides as a recorder of thermocline conditions by measuring the stable oxygen and carbon isotopic compositions of this species from 28 surface sediments in the southwest Pacific near New Zealand. Our data show that G. truncatulinoides (sinistral) calcify mainly in the range of subsurface/thermocline depths in this study region between 100 and 850 m with their carbon isotopes largely corresponding to the surrounding seawater values. To understand the controlling factors of the thermocline δ 13C evolution in the South Pacific, a 260 ka downcore δ 13C record on this species (δ 13C G.trunc) from core site ODP1123 is presented and compared with other δ 13C records. The convergence of δ 13C from thermocline, upper and lower circumpolar deep waters (UCDW/LCDW) during glacial terminations indicates that the deep ocean is the predominant source of increased atmospheric pCO 2 and the δ 13C anomalies in the upper ocean and atmosphere during the deglacials. This is evident in both the South Pacific and South Atlantic. A quantitative calculation of predicted surface ocean δ 13C based on thermodynamic air-sea equilibrium implies this process has a significant control on the temporal thermocline water δ 13C variation over the last glacial-interglacial (G-I) cycle. The lower deglacial δ 13C G.trunc values in the South Atlantic compared to the Pacific further suggest a stronger upwelling in the Atlantic sector of the Southern Ocean, indicating that this was a major ventilation route with an important stock of light δ 13C from the deep waters of this region. This study demonstrates the deep water influence (via upwelling) and atmospheric carbon isotope imprint (via air-sea exchange) on thermocline water δ 13C evolution. It also provides important evidence for the rapid exchange of carbon between the Southern Ocean and atmosphere over multiple G-I cycles. • G. truncatulinoides reliably record thermocline water δ 13C in the SW Pacific. • Importance of air-sea exchange on G-I thermocline water δ 13C signatures. • Stronger upwelling in the Atlantic than the Pacific Southern Ocean at deglaciations. [ABSTRACT FROM AUTHOR]