Our planet is unique in the solar system in having a bimodal distribution of crustal types (continental and oceanic), the presence of liquid water at its surface, an oxygenated atmosphere, and a prolific and diverse biosphere. The evolving yet linked nature of these elements, across the range of spatial and temporal scales that operate on the planet, indicates complex and dynamic cycling between the solid (lithosphere, mantle, and core) and surficial (oceans, atmosphere, and biosphere) reservoirs. This linked evolution occurs in response to heat dissipation from the planet's interior, modulated by input of solar energy to the surficial reservoirs. During its very early history the Earth lacked these crustal and surficial features and, after initial accretion from the solar nebula, likely consisted of a magma ocean (e.g., Elkins-Tanton, 2012). Cooling, density settling, and crystallization resulted in rapid differentiation of the Earth, perhaps over a few tens of millions of years, and included formation of core, mantle, proto-crust, and atmosphere (Figure 1; Elkins-Tanton, 2008. Establishing the cascading succession of

The Midcontinent Rift of North America is a ca. 1.1 Ga, 3000-km-long failed rift that nearly split the Precambrian continent of Laurentia. Unlike most continental rifts, which are filled with a mixture of volcanic rocks and sediments, the Midcontinent Rift contains a large volume of flood basalts that were emplaced during both syn- and post-rift stages. Consequently, the Midcontinent Rift, which comprises the Keweenaw large igneous province, is the most significant positive anomaly on gravity maps of central North America. We investigated the mantle conditions required to produce this large volume of flood basalt and the observed two main stages of emplacement. To explore whether these magma volumes required a plume or, instead, could have resulted from the increased ambient mantle temperatures expected for the Neoproterozoic, we used a geodynamic model for a range of ambient mantle and plume temperatures under different scenarios of lithospheric extension. The most favorable scenario for the generation of both syn-rift and post-rift lavas combines a plume with excess temperatures between 175 and 225 °C introduced during the syn-rift phase and ambient mantle potential temperatures between 1393 and 1443 °C, with an initial lithospheric thickness not exceeding 150 km for 3 mm/yr extension rates.

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