No matter how quiet and pristine a cave setting may appear, all speleothems contain assemblages of magnetic minerals. These iron oxide minerals are derived largely from overlying soils, though minor fractions may come from the residuum of dissolved bedrock, reworked sediment carried by episodic floods, geomicrobiological activity, and even windblown dust. Regardless of their origin, these minerals become aligned with Earth’s ambient magnetic field before they are fixed within a speleothem’s growing carbonate matrix. Here, we describe how the magnetism of stalagmites and flowstone can be used to chronicle high-resolution geomagnetic behavior and environmental change.
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Limits to Gauge Coupling in the Dark Sector Set by the Nonobservation of Instanton-Induced Decay of Super-Heavy Dark Matter in the Pierre Auger Observatory Data
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More than three-quarters of the Earth is covered by the ocean, home to millions of sea creatures. Tiny plants in the surface ocean use energy from the sun to grow, producing the oxygen we breathe. When these plants die, their remains sink like snowflakes into the deeper ocean, where bacteria and small animals break them down through a process called respiration. If respiration happens near the surface, carbon dioxide is released back into the air, but when respiration occurs deeper, the carbon dioxide stays trapped for a long time, helping to regulate Earth’s climate. Scientists face challenges in measuring respiration in the dark, cold, and high-pressure depths of the ocean. In this article, we explore how researchers worldwide are solving this puzzle and how you can help protect ocean life.more » « less
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Abstract We investigate the effect of dark stars (DSs) on the reionization history of the universe, and the interplay between them and feedback due to Lyman–Werner (LW) radiation in reducing the cosmic microwave background (CMB) optical depth to a value within the τ = 0.054 ± 0.007 range measured by Planck. We use a semianalytic approach to evaluate reionization histories and CMB optical depths, which includes Population II stars in atomic cooling halos and Population III stars in minihalos with LW feedback, preceded by a DS phase. We show that while LW feedback by itself can reduce the integrated optical depth to the last scattering surface to ∼0.05 only if the Population III star formation efficiency is less than ∼0.2%, the inclusion of a population of DSs can naturally lead to the measured CMB optical depth for much larger Population III star formation efficiencies ≳1%.more » « less
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