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The polygonal patterns in permafrost regions are caused by the formation of ice wedges. Observations of polygon evolution reveal that rapid ice-wedge melting has occurred across the Arctic since 1950, altering tundra hydrology.
The amount of carbon dioxide in the atmosphere declined as the Earth entered the last glacial period. Estimates of deep carbonate ion concentrations suggest that a substantial amount of carbon was sequestered in the deep Atlantic Ocean.
Assessments of earthquake risk often assume rupture of a single fault. Analysis of a 1997 Pakistan earthquake reveals that not one but two separate ruptures caused the shaking, implying that cascading events should be factored into forecasts.
Magma reservoirs typically accumulate over hundreds to thousands of years. Yet, geochemical analyses of volcanic rocks from Campi Flegrei suggest activity there was triggered by injections of volatile-rich magma only days before the eruption.
The Cryogenian Snowball Earth glaciations were followed by the deposition of massive cap carbonates. Geochemical modelling suggests that shallow-ridge volcanism supplied much of the alkalinity and cations that fuelled this deposition.
How Himalayan topography is built is unclear. Analysis of surface displacement during the 2015 Gorkha earthquake suggests that large earthquakes may lower the high Himalayan mountains, and topography may grow during the interseismic phase.
The time at which plate tectonics were initiated on Earth is unclear. Geochemical analysis of diamonds suggests that recycled oxidized material could have been introduced to the mantle via subduction zones more than 3 billion years ago.