Age (Ga) 3.5 3 2.5 2 1.5 1 0.5 0 Modern seawater Continental crustEukaryotes reached ecological importance in the late Neoproterozoic Era, some one billion years after their emergence. Their slow rise to prominence has been ascribed to prolonged environmental stagnation, but testing this idea requires an appraisal of the evolution of atmospheric and ocean chemistry. Establishing a nuanced geochemical history is, however, challenging due to the paucity of well preserved sedimentary rocks. Here, we present new Mo isotope ratios from black shale units spanning ∼1560 to ∼1170 Ma. These results, combined with literature data, reveal potential episodic expansions of oxygenated and/or mildly reducing conditions during the Mesoproterozoic Era, suggesting fluctuating oxygen availability that could have exerted a crucial control on the evolution of eukaryotes.

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In order to clarify the characteristics of pore-throat in tight sandstone reservoirs in the Dibei area of the Kuqa Depression in the Tarim Basin (Northwest China) and to make clear its impact on reservoir quality and productivity, microscopic observation and quantitative analysis of 310 tight sandstones in the Kuqa Depression are carried out by using various methods. Microscopic observation shows that the shapes of the pores are flat, oval, and long-narrow. A great number of throats connect the nanoscale pores in the form of a network. Quantitative analyses including RCMP (rate-controlled mercury penetration), HPMI (high-pressure mercury injection), NA (nitrogen adsorption), and routine and stress-dependent core analysis show that the peak of pores radius ranges from 125 μm to 150 μm, and the throat radius is in the range of 1 μm-4 μm. The throat space accounts for about 2/3 of the total space of the tight sandstones, which is the major storage space for natural gas. The space shape has a great influence on the reservoir seepage capacity, particularly under the condition of overburden pressure. The pores with throat radius greater than 300 nm have free fluid, and they contribute more than 98% of the reservoir permeability. The pore spaces with throat radius among 300 nm-52 nm can release fluids by reservoir stimulation. The pore-throats with radius < 52   nm cannot release the irreducible hydrocarbon fluids. In addition, formation pressure is easy to destroy tight sandstone reservoir. The research results will provide insights into the efficient recovery of natural gas in tight sandstones.