First N2 Profile for Venus’ Deep Lower Atmosphere

Currently, two competing concepts that both are based on (amongst others) the Fe-Ti systematics of palaeosols, try to describe the evolution of the oxygen content of the Precambrian Earth's atmosphere. One model favours a rapid and significant increase of atmospheric oxygen levels during the Palaeoproterozoic (summarized in Holland, 1994), whereas another suggests that only minor changes of less than _ 50% occurred throughout Earth's history (summarized in Ohmoto, 1997). Although the former is currently more widely accepted than the latter, it suffers from two shortcomings: (i) the validity of the conclusions derived from the palaeosol record rely heavily on the assumption of absence of organic matter from Archaean and Palaeoproterozoic weathering profiles, and (ii) the time of the postulated increase of atmospheric oxygen is rather poorly constrained due to large uncertainties of some palaeosol ages; nevertheless, however, the rapid increase is suggested to have occurred between c. 2.2 and 1.9 Ga B.P. (Holland, 1994). Thus, there is need for (i) other redox-indicators that are able to provide at least qualitative evidence for a rather constant or an increasing redox-level of the Precambrian atmosphere-hydrosphere system, but which are rather insensitive to the presence or absence of organic matter, and (ii) evidence from samples that originate from well-dated profiles with a (for Precambrian standards) reasonably good time resolution. Hence, we studied the distribution of Mn and rareearth elements (REEs) in only slightly metamorphosed chemical platform sediments from the Kuruman and Griquatown Iron-Formations (IFs) and the Hotazel Manganese-Formation (MnF), and in palaeoweathering products in the Transvaal Supergroup, South Africa. While the only abundant primary oxide minerals in the Kuruman and Griquatown IFs are Fe(III) oxides, the Hotazel MnF is the oldest largescale deposit of Mn(III) oxides in the geological record. The results bear clear evidence for a rapid increase of the oxygen content of both, the Earth's ocean and atmosphere between -2.5 and -2.4 Ga B.P.

A Question Raised by the Observed Absence of an Atmosphere in the Moon

We attempted to reproduce the total electron content (TEC) variation in the Earth's atmosphere from the temporal variation of the solar flare spectrum of the X9.3 flare on September 6, 2017. The flare spectrum from the Flare Irradiance Spectral Model (FISM), and the flare spectrum from the 1D hydrodynamic model, which considers the physics of plasma in the flare loop, are used in the GAIA model, which is a simulation model of the Earth's whole atmosphere and ionosphere, to calculate the TEC difference. We then compared these results with the observed TEC. When we used the FISM flare spectrum, the difference in TEC from the background was in a good agreement with the observation. However, when the flare spectrum of the 1D-hydrodynamic model was used, the result varied depending on the presence or absence of the background. This difference depending on the models is considered to represent which extreme ultraviolet (EUV) radiation is primarily responsible for increasing TEC. From the flare spectrum obtained from these models and the calculation result of TEC fluctuation using GAIA, it is considered that the enhancement in EUV emission by approximately 15–35 nm mainly contributes in increasing TEC rather than that of X-ray emission, which is thought to be mainly responsible for sudden ionospheric disturbance. In addition, from the altitude/wavelength distribution of the ionization rate of Earth's atmosphere by GAIA (Ground-to-topside Atmosphere and Ionosphere model for Aeronomy), it was found that EUV radiation of approximately 15–35 nm affects a wide altitude range of 120–300 km, and TEC enhancement is mainly caused by the ionization of nitrogen molecules.

The bulk of the sun's radiation is in the visible and infrared. Solar radiation at these wavelengths controls the weather in the lowest levels of the earth's atmosphere. The rate at which this energy is emitted (the so-called solar constant) varies by a few tenths of 1 percent over a time scale of days. Longer period variations may exist, but have yet to be detected. Far more variable are the amounts of energy emitted as ultraviolet, extreme ultraviolet, and x-rays, and in the continuous outflow of ionized solar particles. The latter controls the properties of the space between the earth and the sun as well as those of the earth's magnetosphere. The ultraviolet and particle emissions control the properties of the earth's upper atmosphere, including the global wind circulation and changes therein associated with intense auroral storms. While considerable progress has been made in exploring the solar-terrestrial system since the advent of space research, many problems remain. These include the question of how magnetic energy is converted into ionized particle energy in the sun and in the earth's magnetosphere, the way in which solar and terrestrial magnetic fields join or merge, and how large electric fields are generated and sustained a few thousand kilometers above the earth's poles. Perhaps the most intriguing question concerns the possible relation between solar variability and the earth's weather and climate.

The evolution of plants from water to land was a transformative event that reshaped Earth's ecosystems and atmosphere. Originating from freshwater charophyte algae, early plants developed critical adaptations such as cuticles, stomata, desiccation‐resistant spores, vascular tissues, roots and seeds. These innovations enabled survival in terrestrial environments and drove the diversification of major lineages, including bryophytes, vascular plants, gymnosperms and angiosperms. Key drivers of this transition included ecological opportunities in unoccupied niches, environmental pressures like desiccation, and symbioses with fungi and bacteria. Early plants profoundly influenced Earth's systems by reducing atmospheric CO 2 , forming soils and increasing oxygen levels. Despite advances, gaps remain in the fossil record, genetic mechanisms and environmental contexts of this transition. Understanding these processes is vital for reconstructing plant evolution and addressing modern challenges like climate change and habitat restoration. Thus, this article aims to provide a comprehensive overview of how plants shaped the planet's ecosystems and offer insights into the ongoing adaptation and resilience of plant species in today's rapidly changing world. Key Concepts Plants evolved from aquatic photosynthetic organisms before adapting to land. Vascular tissues (xylem and phloem) revolutionised water and nutrient transport, enabling plants to grow taller and colonise diverse habitats. Seed evolution allowed plants to reproduce independently of water. Terrestrial plants start transforming Earth's atmosphere through CO 2 sequestration and oxygenation. Genetic innovations enabling key adaptations for life on land. Early plants contributed significantly to soil stabilisation and weathering, altering terrestrial landscapes and nutrient cycles.

The boring billion? – Lid tectonics, continental growth and environmental change associated with the Columbia supercontinent

Using the large-eddy simulation framework, effects of an aerosol layer on warm cumulus clouds in the Korean Peninsula when the layer is above or around the cloud tops in the upper atmosphere are examined. Also, these effects are compared to effects of an aerosol layer when it is around or below the cloud bases in the low atmosphere. Simulations show that when the aerosol layer is in the low atmosphere, aerosols absorb solar radiation and radiatively heat up air enough to induce greater instability, stronger updrafts and more cloud mass than when the layer is in the upper atmosphere. As aerosol concentrations in the layer decrease, the aerosol radiative heating gets weaker to lead to less instability, weaker updrafts and less cloud mass when the layer is in the low atmosphere. This in turn makes differences in cloud mass, which are between a situation when the layer is in the low atmosphere and that when the layer is in the upper atmosphere, smaller. It is found that the transportation of aerosols by updrafts reduces aerosol concentrations in the aerosol layer, which is in the low atmosphere, and in turn reduces the aerosol radiative heating, updraft intensity and cloud mass. It is also found that the presence of aerosol impacts on radiation suppresses updrafts and reduces clouds. Aerosols affect not only radiation but also aerosol activation. In the absence of aerosol impacts on radiation, aerosol impacts on the droplet nucleation increases cloud mass when the layer is in the low atmosphere as compared to a situation when the layer is in the upper atmosphere. As aerosol impacts on radiation team up with those on the droplet nucleation, differences in cloud mass, which are between a situation when the layer in the low atmosphere and that when the layer is in the upper atmosphere, get larger. This is as compared to a situation when there is no aerosol impacts on radiation and only aerosol impacts on the droplet nucleation.

It is widely accepted that Earth's early atmosphere contained less than 0.001 per cent of the present-day atmospheric oxygen (O2) level, until the Great Oxidation Event resulted in a major rise in O2 concentration about 2.4 billion years ago. There are multiple lines of evidence for low O2 concentrations on early Earth, but all previous observations relate to the composition of the lower atmosphere in the Archaean era; to date no method has been developed to sample the Archaean upper atmosphere. We have extracted fossil micrometeorites from limestone sedimentary rock that had accumulated slowly 2.7 billion years ago before being preserved in Australia's Pilbara region. We propose that these micrometeorites formed when sand-sized particles entered Earth's atmosphere and melted at altitudes of about 75 to 90 kilometres (given an atmospheric density similar to that of today). Here we show that the FeNi metal in the resulting cosmic spherules was oxidized while molten, and quench-crystallized to form spheres of interlocking dendritic crystals primarily of magnetite (Fe3O4), with wüstite (FeO)+metal preserved in a few particles. Our model of atmospheric micrometeorite oxidation suggests that Archaean upper-atmosphere oxygen concentrations may have been close to those of the present-day Earth, and that the ratio of oxygen to carbon monoxide was sufficiently high to prevent noticeable inhibition of oxidation by carbon monoxide. The anomalous sulfur isotope (Δ(33)S) signature of pyrite (FeS2) in seafloor sediments from this period, which requires an anoxic surface environment, implies that there may have been minimal mixing between the upper and lower atmosphere during the Archaean.

The gas‐phase photolysis of H2O at 1849 Å in the presence of CO yields mainly CO2 and H2 and a variety of organic compounds, including C1−C3 hydrocarbons, alcohols, aldehydes, acetone, and acetic acid. The overall quantum yield for conversion of CO to organic compounds varies between 0.23 and 0.03 as a function of the CO abundance. These results indicate that even if primitive earth's atmosphere initially contained no molecular hydrogen and contained carbon only in the form of CO or a mixture of CO and CO2, the prebiotic environment would have become enriched with a variety of organic compounds produced by photochemical processes.

Reconstructions of ancient ecological interactions rely upon information found in rocks deposited at Earth's surface billions of years ago. Geologic and geochemical evidences of the nature of early Earth are widely dispersed in isolated outcrops across the globe and are imperfectly preserved. In addition to the impediments to understanding imposed by a fragmentary historical record, knowledge must be gained from studying modern environments in order to interpret evidence gleaned from Earth's oldest rocks. The application of data measured on modern samples to decipher clues hidden in ancient rocks necessitates extrapolating several billion years in time, a problematical exercise at best. There is an inevitable logical circularity in accepting the present as the key to the past: But, what other benchmark does one have? This presentation will explain how geological and geochemical evidence is used to constrain hypotheses for the evolution of Earth's atmosphere, biosphere, hydrosphere, and lithosphere, prior to 2.5 billion years ago.

Abstract— Meteor science, aeronomy, and meteoritics are different disciplines with natural interfaces. This paper is an effort to integrate the chemistry and mineralogy of collected interplanetary dust particles (IDPs), micrometeorites, and meteorites with meteoric data and with atmospheric metal abundances. Evaporation, ablation, and melting of decelerating materials in the Earth's atmosphere are the sources of the observed metal abundances in the upper atmosphere. Many variables ultimately produce the materials and phenomena we can analyze, such as different accretion and parent‐body histories of incoming extraterrestrial materials, different interactions of meteors with the Earth's middle atmosphere, meteor data reduction, and complex chemical interactions of the metals and ions with the ambient atmosphere. The IDP‐like and unequilibrated ordinary chondrite matrix materials are reasonable sources for observed meteoric and atmospheric metals. The hypothesis of hierarchical dust accretion predicts that low, correlated refractory element abundances in cometary meteors may be real. It implies that the CI or cosmic standard is not useful to appreciate the chemistry of incoming petrologically heterogeneous cometary matter. The quasi steady‐state metal abundances in the lower thermosphere and upper mesosphere are derived predominantly from materials with cometary orbital characteristics and velocities such as comets proper and near‐Earth asteroids. The exact influence of atmospheric chemistry on these abundances still needs further evaluation. Metal abundances in the lower mesosphere and upper stratosphere region are mostly from materials from the asteroidal belt and the Kuiper belt.

Reinterpretations of telemetry data returned to earth from the Pioneer Venus Orbiter suggest that the surface of Venus may be characterized by violent immense volcanic activity. L.W. Esposito has made an interactive analysis of Pioneer ultraviolet spectral data and similar data from the earth's atmosphere [Science, 223, 1072–1074, 1984]. Spacecraft analysis of sulfur dioxide in the earth's upper atmosphere, apparently released by El Chich[acu]on, Mexico, in March 1982 (EOS, June 14, 1983, p. 411, and August 16, 1983, p. 506) prompted reanalysis of accumulated Pioneer ultraviolet data. Massive injections of sulfur dioxide into the Venus atmosphere could be the result of volcanic eruptions about the size of the Krakatoa explosive eruption that took place between Java and Summatra in 1883.

Radiative equilibrium solutions are the starting point in our attempt to understand how the atmospheric composition governs the surface and atmospheric temperatures, and the greenhouse effect. The Schwarzschild analytical grey gas model (SGM) was the workhorse of such attempts. However, the solutions suffered from serious deficiencies when applied to Earth's atmosphere and were abandoned about 3 decades ago in favor of more sophisticated computer models. Here we show that simple heuristic modifications to the SGM resolve these deficiencies, at least the catastrophic ones. The modifications include the addition of a spectral window, as well as allowing the scale height of optical depth to be different from that of the atmospheric pressure. The modified SGM reveals the fundamental factors that govern the radiative equilibrium thermal structure. (1) The presence of a spectral window allows the temperature jump between the surface and the immediately overlying atmosphere to become small, irrespective of the magnitude of the surface temperature. (2) In an optically thick atmosphere (such as Earth and Venus), the surface temperature and the runaway greenhouse effect depend inversely (as the one‐fourth power) on the Planck function‐weighted width of the window and are independent of the optical depth and other atmospheric parameters. The vertical variation of temperature within the atmosphere, however, is determined by the vertical variation of optical depth. (3) The degree of convective instability of the radiative equilibrium thermal structure γ is proportional to the ratio H/Hτ, where H is the atmospheric scale height and Hτ is the scale height of the vertical variation of optical depth. Here, γ is the ratio of the radiative equilibrium lapse rate and the neutral lapse rate for dry convection; γ > 1 indicates that the profile is unstable to free convection. Thus Hτ < H emerges as one of the fundamental criteria for convective instability. These factors lead to several corollaries regarding the specific details of atmospheric thermal structure on Earth and Venus. For example, according to the modified SGM, the radiative equilibrium temperature profile is strongly superadiabatic in Earth's lower atmosphere because Hτ is dominated by the water vapor's scale height being much less (2 compared with 8 km) than the atmospheric scale height. In the case of Venus, the pressure broadening of the CO2 rotational lines makes Hτ a factor of 2 smaller than H. Some of these results have been obtained using more detailed, multispectral radiative equilibrium models.

Abstract. We present a new routine for calculating the non-local thermodynamic equilibrium (non-LTE) 15 µm CO2 cooling–heating of mesosphere and lower thermosphere in general circulation models. It uses the optimized models of the non-LTE in CO2 for day and night conditions and delivers cooling–heating with an error not exceeding 1 K d−1 even for strong temperature disturbances. The routine uses the accelerated lambda iteration and opacity distribution function techniques for the exact solution of the non-LTE problem and is about 1000 times faster than the standard matrix and line-by-line solution. It has an interface for feedbacks from the model and is ready for implementation. It may use any quenching rate coefficient of the CO2(ν2)+O(3P) reaction, handles large variations in O(3P), and allows the user to vary the number of vibrational levels and bands to find a balance between the calculation speed and accuracy. The suggested routine can handle the broad variation in CO2 both below and above the current volume mixing ratio, up to 4000 ppmv. This allows the use of this routine for modeling Earth's ancient atmospheres and the climate changes caused by increasing CO2.

The high concentration of molecular oxygen in Earth's atmosphere is arguably the most conspicuous and geologically important signature of life. Earth's early atmosphere lacked oxygen; accumulation began after the evolution of oxygenic photosynthesis in cyanobacteria around 3.0-2.5billion years ago (Gya). Concentrations of oxygen have since varied, first reaching near-modern values ~600 million years ago (Mya). These fluctuations have been hypothesized to constrain many biological patterns, among them the evolution of body size. Here, we review the state of knowledge relating oxygen availability to body size. Laboratory studies increasingly illuminate the mechanisms by which organisms can adapt physiologically to the variation in oxygen availability, but the extent to which these findings can be extrapolated to evolutionary timescales remains poorly understood. Experiments confirm that animal size is limited by experimental hypoxia, but show that plant vegetative growth is enhanced due to reduced photorespiration at lower O(2):CO(2). Field studies of size distributions across extant higher taxa and individual species in the modern provide qualitative support for a correlation between animal and protist size and oxygen availability, but few allow prediction of maximum or mean size from oxygen concentrations in unstudied regions. There is qualitative support for a link between oxygen availability and body size from the fossil record of protists and animals, but there have been few quantitative analyses confirming or refuting this impression. As oxygen transport limits the thickness or volume-to-surface area ratio-rather than mass or volume-predictions of maximum possible size cannot be constructed simply from metabolic rate and oxygen availability. Thus, it remains difficult to confirm that the largest representatives of fossil or living taxa are limited by oxygen transport rather than other factors. Despite the challenges of integrating findings from experiments on model organisms, comparative observations across living species, and fossil specimens spanning millions to billions of years, numerous tractable avenues of research could greatly improve quantitative constraints on the role of oxygen in the macroevolutionary history of organismal size.