Browsing by Author "Seales, Johnny"
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Item Buffering of mantle conditions through water cycling and thermal feedbacks maintains magmatism over geologic time(Springer Nature, 2022) Seales, Johnny; Lenardic, Adrian; Richards, MarkThe Earth has remained magmatically and volcanically active over its full geologic history despite continued planetary cooling and a lack of thermal equilibrium in the mantle. Here we investigate this conundrum using data-constrained numerical models of deep-water cycling and thermal history. We find that the homologous temperature - the ratio of upper mantle to melting temperatures - initially declined but has been buffered at a nearly constant value since 2.5-2.0 billion years ago. Melt buffering is a result of the dependence of melting temperature and mantle viscosity on both mantle temperature and water content. We show that thermal and water cycling feedbacks lead to a self-regulated mantle evolution, characterised by a near-constant mantle viscosity. This occurs even though the mantle remains far from thermal equilibrium. The added feedback from water-dependent melting allows magmatism to be co-buffered over geological time. Thus, we propose that coupled thermal and water cycling feedbacks have maintained melting on Earth and associated volcanic/magmatic activity.Item Influence of the asthenosphere on earth dynamics and evolution(Springer Nature, 2023) Cathles, Lawrence; Fjeldskar, Willy; Lenardic, Adrian; Romanowicz, Barbara; Seales, Johnny; Richards, MarkThe existence of a thin, weak asthenospheric layer beneath Earth’s lithospheric plates is consistent with existing geological and geophysical constraints, including Pleistocene glacio-isostatic adjustment, modeling of gravity anomalies, studies of seismic anisotropy, and post-seismic rebound. Mantle convection models suggest that a pronounced weak zone beneath the upper thermal boundary layer (lithosphere) may be essential to the plate tectonic style of convection found on Earth. The asthenosphere is likely related to partial melting and the presence of water in the sub-lithospheric mantle, further implying that the long-term evolution of the Earth may be controlled by thermal regulation and volatile recycling that maintain a geotherm that approaches the wet mantle solidus at asthenospheric depths.Item Mixed heating velocity scaling input files(Rice University, 2020-09-29) Lenardic, Adrian; Seales, Johnny; Moore, William B.; Weller, Matthew B.; Earth, Environmental, and Planetary SciencesThe input files were used to explore the effects of mixed heating on convective velocity scalingItem OW1 Data InOut(Rice University, 2020-08-20) Seales, Johnny; Lenardic, Adrian; Earth, Environmental, and Planetary SciencesThe parameter inputs and data outputs provided herein were used to establish the hypothesis that changes in deep water cycling lead to a multi-stage cooling of the Earth.Item Uncertainty and Hypothesis Testing in Planetary Thermal History Models(2020-04-23) Seales, Johnny; Lenardic, AdrianPlate tectonics convectively cools the Earth at present. Debate remains in defining plate tectonics as a dynamic system. What is the primary resistor to plate motions: plates, mantle viscosity, some mixture of the two? Here I shed some light on this debate. First, I quantify the uncertainties associated with the different hypotheses. Then, I constrain the probability that different thermal paths from each of these hypotheses match Earth's geologic proxy data. Only a single hypothesis is true for Earth. The data, however, cannot tell us which. So, rather than using the most probable hypothesis, we can embrace this uncertainty. Each successful thermal path informs us of how other plate tectonic planetary interiors may have evolved in the past or will evolve in the future. Another question arises from inspecting Earth's thermal history data: what is the convective mechanism for the multi-stage cooling present in some sets of thermal history data? I show that changes in the deep water cycle, namely a switch from a net dehydrating to rehydrating mantle, can act as this mechanism. If this mechanism is true, it may directly influence surface conditions. This may be important for determing whether a planet can maintain liquid water at its surface. Interior processes, then, may play a vital role in determining the inhabitance of a planet. This leaves many searches for life on exoplanets fixated on finding Earth2.0. Depending on the question we ask, however, this may be the wrong approach. I demonstrate that if we cast a broader net in our search for inhabited planets, the increased reward likely outweighs the increased cost.