The soil samples collected from the Garhwal region, Uttaranchal, NW Lesser Himalaya are characterised by fine to medium grained textures with brown and black as major colours. The soil samples have variable silica contents ranging from 55-72 wt% with moderate SiO₂/Al₂O₃, K₂O/Na₂O ratios but relatively high Fe₂O₃ + MgO (5-6 wt%) and moderate CaO contents. Relative to the post-Archean North American Shale Composite (NASC) and Post Archean Average Shales from Australia (PAAS), the Garhwal samples have lower large ion lithophile elements (LILE) and high field strength elements (HFSE) abundances and exhibit negative anomalies in a NASC-normalised spider diagram. The wide spectrum of SiO₂ contents, large variation in ratios like Cr/Zr (0.3-3.5), Sc/Th (0.6-2.43), Th/U(> 2), Th/Co and Zr/Y indicate that the weathering of mostly felsic rocks with minor inputs of mafic rocks might have played an important role in producing these soils. In the discrimination functions (Fl-F2) diagram, the Garhwal samples exhibit scattered pattern and plot in the fields of Quartzose sedimentary provenance, intermediate igneous provenance and mafic igneous provenance thus substantiating the above inference. The relationship among alkali and alkaline earth elements, the chemical index of alteration (CIA) suggests that the source rocks have undergone moderate chemical weathering. The weathering conditions of any source region can also be depicted from Al₂O₃(A)-CaO + Na₂O(CN)-K₂O(K) diagram. The soil samples plot near idealized average shale composition and between shale and granodiorite in A-CN-K diagram pointing towards moderate weathering history of the source region.
    Despite the fact that the study area is more favourable for physical, chemical and biological weathering, striking similarities were observed between the composition of soils and source/bed rocks without much loss of elements. This inference has led to the conclusion that the area is undergoing periodic neotectonic activity.

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The oxygenation of the atmosphere produced some irreversible changes in the Earth's history, including evolution of higher biological forms. Several aspects of this important process, such as its timing and causes, have remained subjects of debate. The present review is an attempt to provide an update on issues related to the evolution of atmospheric oxygen during the Precambrian. It is generally believed that the amount of atmospheric oxygen increased during the Paleoproterozoic despite the fact that photosynthesis originated much earlier in the Earth's history. The pattern of Fe retention in paleosols and the record of mass-independent fractionation in sulfur isotopes confirm that the transition to more oxidizing conditions took place during the Paleoproterozoic.
    Various mechanisms, ranging from an increase in the sources of oxygen to a decrease in its sinks, have been envisaged as processes causing the oxygen rise during the Paleoproterozoic. Conventionally, it is believed that the burial of photosynthetic carbon has allowed the establishment of oxygen. However, the transition in mantle oxidation states and the escape of hydrogen during photolysis of methane of biogenic origin have also been suggested as having played an important role in the establishment of free molecular oxygen in the atmosphere-hydrosphere system. The coincidence of timing of the oxygen rise and the positive excursions in carbon isotope compositions of carbonate rocks during the Paleoproterozoic suggests an important role for the carbon cycle in atmospheric oxygen evolution.
    Better quantitative modeling of atmospheric oxygen levels may be essential to allow full comprehension of the timing, causes and consequences of the oxygen rise in the Earth's history. Quantitative modeling is essential as it can lead to an unraveling of the co-evolutionary nature of the surface environment and the biosphere of the Earth.

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The volcanic suite of the Ghayth area forms the lowermost lavas of the Oman ophiolite extrusives within Oman ophiolite. Ghayth area is located within Fizh block, one of the northern blocks of the Oman ophiolite. The lithological succession in the Ghayth area consists of Units 1a and 1b (Geotimes Unit, Lasail Unit) overlain by Unit 2 (Clinopyroxene-phyric Unit). Texturally, Unit 1a lavas are dominantly aphyric, with few plagioclase and clinopyroxene clots and microphenocrysts. In contrast, Unit 1b lavas are sparsely to moderately phyric with clinopyroxene, plagioclase (altered to albite) and olivine pseudomorphs (replaced by clay minerals) in sub-ophitic texture in intersertal-intergranular groundmass consisting of albite laths and devitrified mesostasis (altered to clay minerals). Unit 2 lavas are glomerophyritic with clinopyroxene and olivine (pseudomorphed by calcite) glomerocrysts surrounded by plagioclase microlites and devitrified mesostasis (partly altered to calcite).
    The minor elements data from clinopyroxenes indicate those Units 1a, 1b and 2 showing tholeiitic basalt signatures but with island arc affinities for Unit 2. However, the triangular discrimination diagram of (Y-La-Nb) for bulk analyses indicated that Units 1a and 1b are falling where the three fields of N-MORB(Normal Mid Ocean Ridge Basalt), back arc basin basalt and island arc tholeiite all meet. The clinopyroxenes and bulk chemical compositions of Unit 1a lavas are more evolved and are characterized by enrichment of incompatible HFSEs, REEs (High Field Strength Elements, Rare Earth Elements) and depletion of Cr and Ni relative to the less evolved Unit 1b lavas (which are richer in Cr and Ni and low in HFSEs and REEs abundances). Correlations between Mg# (Magnesium number) and selected major, minor and trace element concentrations indicate their single mantle sources with different magmatic fractionation events. The spider diagram patterns of selected bulk rock trace elements show that Units 1a and 1b have a pattern of mixed affinities between N-MORB and back-arc basin. This is coupled with the Nb/Ta and Zr/Hf depletions relative to N-MORB and the mildly depleted to flat LREE patterns, indicating that their mantle sources are possibly contaminated with back-arc basin signatures. Therefore, these lavas might have erupted in the back-arc spreading center.

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