Important Missing Information Research Articles

Lunar And Planetary Perspectives On The Geological History Of The Earth

During the latter part of the last century, a profound change took place in our perception of the Earth. First, this change was holistic: Plate tectonic theory provided a unifying theme that seems to explain disparate observations about the Earth and how it works, and lets us see the Earth as a planet. Secondly, actually seeing the Earth from the Moon, and exploring the other planets provided additional perspectives on our own home planet and hastened the decline of scientific terracentrism. Thirdly, learning that the uniqueness of the Moon in terms of size and aspects of its chemistry may be due to its derivation from the Earth as the result of a giant impact, provided a concrete filial link. Finally, the geological record revealed by exploration of the Moon and planets has provided us with the missing chapters in the dynamic history of the Earth. We now know that gargantuan impact basins formed in Earth's formative years and that impact events are likely to be the cause of many punctuations in Earth's biological evolution. Perspectives on ancient tectonic activity are provided by Mercury, Venus, Mars, and the Moon, and show that the Earth has changed considerably since its youth. Widely varying volcanic eruption styles are seen on the planets, providing insight into how puzzling rocks from early Earth history formed. The composition of planetary atmospheres has revealed the unusual nature of Earth's, and its link to the evolution of life. The atmospheres of the planets have undergone radical changes with time, providing clues to Earth's history and destiny. Fundamentally different hydrological cycles on Earth, Venus, Europa and Mars, and evidence for significant changes with time, have provided insight into Earth's history. The probable presence of oceans on Europa and Mars has changed our thinking about the origin and evolution of life on Earth. We no longer think of the Earth in isolation. Instead, Earth is now perceived of as a member of a family of planets, each of which provides important missing information and perspective on the other, and together reveal the fabric of the history of the Solar System. Future exploration and perspectives will place our Solar System in the context of all of the others.

Photochemical modeling of hydroxyl and its relationship to other species during the Tropospheric OH Photochemistry Experiment

Because of the extremely short photochemical lifetime of tropospheric OH, comparisons between observations and model calculations should be an effective test of our understanding of the photochemical processes controlling the concentration of OH, the primary oxidant in the atmosphere. However, unambiguous estimates of calculated OH require sufficiently accurate and complete measurements of the key species and physical variables that determine OH concentrations. The Tropospheric OH Photochemistry Experiment (TOHPE) provides an extremely complete set of measurements, sometimes from multiple independent experimental platforms, that allows such a test to be conducted. When the calculations explicitly use observed NO, NO2, hydrocarbons, and formaldehyde, the photochemical model consistently overpredicts in situ observed OH by ∼50% for the relatively clean conditions predominantly encountered at Idaho Hill. The model bias is much higher when only CH4‐CO chemistry is assumed, or NO is calculated from the steady state assumption. For the most polluted conditions encountered during the campaign, the model results and observations show better agreement. Although the comparison between calculated and observed OH can be considered reasonably good given the ±30% uncertainties of the OH instruments and various uncertainties in the model, the consistent bias suggests a fundamental difference between theoretical expectations and the measurements. Several explanations for this discrepancy are possible, including errors in the measurements, unidentified hydrocarbons, losses of HOx to aerosols and the Earth's surface, and unexpected peroxy radical chemistry. Assuming a single unidentified type of hydrocarbon is responsible, the amount of additional hydrocarbon needed to reduce theoretical OH to observed levels is a factor of 2 to 3 greater than the OH‐reactivity‐weighted hydrocarbon content measured at the site. Constraints can be placed on the production and yield of various radicals formed in the oxidation sequence by considering the observed levels of certain key oxidation products such as formaldehyde and acetaldehyde. The model results imply that, under midday clean westerly flow conditions, formaldehyde levels are fairly consistent with the OH and hydrocarbon observations, but observed acetaldehyde levels are a factor of 4 larger than what is expected and also imply a biogenic source. Levels of methacrolein and methylvinylketone are much lower than expected from steady state isoprene chemistry, which implies important removal mechanisms or missing information regarding the kinetics of isoprene oxidation within the model. In a prognostic model application, additional hydrocarbons are added to the model in order to force calculated OH to observed levels. Although the products and oxidation steps related to pinenes and other biogenic hydrocarbons are somewhat uncertain, the addition of a species with an oxidation mechanism similar to that expected from C10 pinenes would be consistent with the complete set of observations, as opposed to naturally emitted isoprene or any of the anthropogenic hydrocarbons examined in the model. Further constraints on the abundance of peroxy radicals are necessary in order to fill the gaps in our understanding of OH photochemistry for the clean continental conditions typical of Idaho Hill.

Derivation of soil water capacity parameters from standard soil texture information for Bulgarian soils

Prediction of total porosity and volumetric water content at field capacity, and permanent wilting point have been evaluated for their possible applicability to supply important missing soil information. The results were compared to the experimental data from Bulgaria. Also the possibility is explored to convert soil particle size distribution data as determined according to the soil standards in Bulgaria to the following particle size fractions (‘sand’ (0.05–2.0 mm in diameter), ‘silt’ (0.002–0.05 mm) and ‘clay’ (smaller than 0.002 mm)). The approach tested for calculating total porosity and volumetric water content at field capacity, and permanent wilting point yielded values in close agreement with the measured ones.

Entropy, likelihood and phase determination.

Entropy, likelihood and phase determination.