Delivery of bioavailable iron and other bioessential metals to the sea surface influences the ocean-climate system through stimulation of marine primary productivity and organic carbon export in areas where eolian iron input is low, such as the Southern Ocean. In these regions, extraterrestrial dust may provide a significant fraction of bioavailable iron, due to the high reactivity of re-condensed material following ablation. If so, past episodes of increased extraterrestrial dust flux should be evident in lithologic, and potentially climatic, records. Here we show that the well-documented increase in extraterrestrial flux associated with the Ordovician L-chondrite parent-body breakup is close in time to proliferation of ooidal ironstones on continental shelves. We hypothesize that benthic iron flux from shelf sediments was increased by expanded oxygen minimum zones driven by broader regions of increased primary productivity. A later Mesozoic interval of global proliferation of ooidal ironstones and black shales also occurs at a peak in asteroid family ages formed by major main-belt collisions. Although internal forcings and feedbacks, such as global tectonic and magmatic processes, play the dominant control on long-term changes in biogeochemical cycles and related marine lithologic records, we suggest that extraterrestrial dust flux may play a role as an external forcing on Earth's climate system.
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