The long-term cooling of Earth’s mantle is recorded in the declining temperature and volume of its volcanic outpourings over time. However, analyses of 89-million-year-old lavas from Costa Rica suggest that extremely hot mantle still lurks below.

Abstract

Earth’s history has been punctuated by vast magmatic episodes. These events are preserved in the geological record as large igneous provinces — areas of Earth’s surface flooded by millions of cubic kilometres of lava that erupted in short periods of time1. Thought to be triggered by upwelling plumes of hot mantle2, the size and frequency of these volcanic episodes may have been greater in the past, fuelled by the hotter mantle of Earth’s Archaean eon3. During this time, a distinctive type of igneous rock — komatiite — formed from magmas with high eruption temperatures that cooled to grow long needle-like olivine crystals4,5 (Fig. 1). The rarity of komatiite eruptions more recently in Earth’s history4 is taken as evidence of the mantle’s slow cooling3,6. However, komatiitic lavas that formed 89 million years ago from the volcanic outpourings of the nascent Galápagos plume have been found in the Tortugal suite of the Caribbean large igneous province7. Writing in Nature Geoscience, Trela et al.8 demonstrate that these lavas formed from anomalously hot mantle with a temperature similar to that which produced the ancient Archaean komatiites, challenging our view of Earth’s thermal structure and history.