Episodic warm climates on early Mars primed by crustal hydration
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Gravitational stability of iron-rich peridotite melt at Mars’ core-mantle boundary
Possible existence of dense iron-rich silicate melt layer above Mars’ core is important in understanding the nature and evolution of Mars. However, gravitational stability of iron-rich silicate melt in the Mars’ interior has not been well constrained, due to experimental difficulties in measuring density of iron-rich peridotitic melt. Here we report density measurements of iron-rich peridotitic melts up to 2465 K by using electrostatic levitation furnace at the International Space Station. Our experimentally obtained densities of iron-rich peridotitic melts are markedly higher than those calculated by first principles simulation, and are distinct from those estimated by extrapolating a density model for SiO2-rich basaltic melts. Our determined density model suggests that peridotitic melt with the Fe/(Mg+Fe) ratio more than 0.4-0.5 has higher density than that at the base of the Mars’ mantle, which indicates gravitational stability of the iron-rich peridotitic melt at the core-mantle boundary in Mars.
Dichotomy retreat and aqueous alteration on Noachian Mars recorded in highland remnants
The Mawrth Vallis region is a plateau situated on the highland side of Mars’ hemispheric dichotomy boundary. It has a >200-m-thick phyllosilicate-bearing stratigraphic succession that indicates extensive aqueous alteration between 4.1 Ga and 3.7 Ga, during the Noachian Period. In addition, thousands of kilometre-scale isolated mounds in the lowlands north and west of Mawrth Vallis have been identified. Here we use geomorphological and spectroscopic analyses to show that the mounds are erosional remnants that formed through retreat of the highland plateau in the Noachian. Consequently, the escarpment that marks the surface expression of the dichotomy must have receded south-southeast by hundreds of kilometres in this area. Lateral and stratigraphic geochemical variation in the mounds show that widespread, multiphase aqueous alteration occurred in situ across this region in surface and subsurface environments. The mound succession is underlain by a pyroxene-rich unit that represents unaltered material below the regional phyllosilicate-bearing sequence and is unconformably overlain by a thin capping unit that marks the end of large-scale regional aqueous activity. Thus, the mounds contain a stratigraphic record of the onset, evolution and cessation of Noachian aqueous conditions in this region, detailing the environment and climate of Mars at its most habitable.
Neural codes track prior events in a narrative and predict subsequent memory for details
Throughout our lives, we learn schemas that specify what types of events to expect in particular contexts and the temporal order in which these events usually occur. Here, our first goal was to investigate how such context-dependent temporal structures are represented in the brain during processing of temporally extended events. To accomplish this, we ran a 2-day fMRI study (N = 40) in which we exposed participants to many unique animated videos of weddings composed of sequences of rituals; each sequence originated from one of two fictional cultures (North and South), where rituals were shared across cultures, but the transition structure between these rituals differed across cultures. The results, obtained using representational similarity analysis, revealed that context-dependent temporal structure is represented in multiple ways in parallel, including distinct neural representations for the culture, for particular sequences, and for past and current events within the sequence. Our second goal was to test the hypothesis that neural schema representations scaffold memory for specific details. In keeping with this hypothesis, we found that the strength of the neural representation of the North/South schema for a particular wedding predicted subsequent episodic memory for the details of that wedding.
Increased early-season productivity drives earlier peak of vegetation photosynthesis across the Northern Hemisphere
Changes in vegetation carbon uptake are largely influenced by the timing and magnitude of the peak of the growing season (POS), when vegetation photosynthesis reaches its maximum. However, the factors controlling the timing of POS remain poorly understood, leaving us uncertain about its future trajectory. Using satellite observations and carbon flux measurements, we show that, in recent decades, increased early-season carbon uptake has been driven by both an earlier onset of the growing season and higher temperatures. In 93% of northern (>30°N) vegetation, these increases in early-season carbon uptake were associated with an advancement of POS. This ongoing shift suggests a developmental constraint on seasonal productivity, potentially limiting carbon uptake later in the season. Our findings provide a mechanistic explanation that reconciles previous observations linking earlier growing season onset, rising temperatures, and shifts in POS timing, and suggest a decrease in late-season carbon uptake with climate warming.
Mitochondrial priming and response to BH3 mimetics in “one-two punch” senogenic-senolytic strategies
A one-two punch sequential regimen of senescence-inducing agents followed by senolytic drugs has emerged as a novel therapeutic strategy in cancer. Unfortunately, cancer cells undergoing therapy-induced senescence (TIS) vary widely in their sensitivity to senotherapeutics, and companion diagnostics to predict the response of TIS cancer cells to a specific senolytic drug are lacking. Here, we hypothesized that the ability of the BH3 profiling assay to functionally measure the mitochondrial priming state—the proximity to the apoptotic threshold—and the dependencies on pro-survival BCL-2 family proteins can be exploited to inform the sensitivity of TIS cancer cells to BH3-mimetics. Replicative, mitotic, oxidative, and genotoxic forms of TIS were induced in p16-null/p53-proficient, BAX-deficient, and BRCA1-mutant cancer cells using mechanistically distinct TIS-inducing cancer therapeutics, including palbociclib, alisertib, doxorubicin, bleomycin, and olaparib. When the overall state of mitochondrial priming and competence was determined using activator peptides, the expected increase in overall mitochondrial priming was an exception rather than a generalizable feature across TIS phenotypes. A higher level of overall priming paralleled a higher sensitivity of competent TIS cancer cells to BCL-2/BCL-xL- and BCL-xL-targeted inhibitors when comparing TIS phenotypes among themselves. Unexpectedly, however, TIS cancer cells remained equally or even less overally primed than their proliferative counterparts. When sensitizing peptides were used to map dependencies on anti-apoptotic BCL-2 family proteins, competent TIS cancer cells appeared to share a dependency on BCL-xL. Furthermore, regardless of senescence-inducing therapeutic, stable/transient senescence acquisition, or genetic context, all TIS phenotypes shared a variable but significant senolytic response to the BCL-xL-selective BH3 mimetic A1331852. These findings may help to rethink the traditional assumption of the primed apoptotic landscape of TIS cancer cells. BCL-xL is a conserved anti-apoptotic effector of the TIS BCL2/BH3 interactome that can be exploited to maximize the efficacy of “one-two punch” senogenic-senolytic strategies.
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