Mechanistic Links Between the Sedimentary Redox Cycle and Marine Acid-Base Chemistry

The redox state of Earth's surface is controlled on geological timescales by the flow of electrons through the sedimentary rock cycle, mediated largely by the weathering and burial of C‐S‐Fe phases. These processes buffer atmospheric pO₂. At the same time, CO₂ influxes and carbonate burial control seawater acid‐base chemistry and climate over long timescales via the carbonate‐silicate cycle. However, these two systems are mechanistically linked and impact each other via charge balance in the hydrosphere. Here, we use a low‐order Earth system model to interrogate a subset of these connections, with a focus on changes that occur during perturbations to electron flow through the sedimentary rock cycle. We show that the net oxidation or reduction of the Earth's surface can play an important role in controlling acid‐base processes in the oceans and thus climate, and suggest that these links should be more fully integrated into interpretive frameworks aimed at understanding Earth system evolution throughout Precambrian and Phanerozoic time

An orbital window into the ancient Sun's mass

Models of the Sun's long-term evolution suggest that its luminosity was substantially reduced 2-4 billion years ago, which is inconsistent with substantial evidence for warm and wet conditions in the geological records of both ancient Earth and Mars. Typical solutions to this so-called "faint young Sun paradox" consider changes in the atmospheric composition of Earth and Mars, and while attractive, geological verification of these ideas is generally lacking-particularly for Mars. One possible underexplored solution to the faint young Sun paradox is that the Sun has simply lost a few percent of its mass during its lifetime. If correct, this would slow, or potentially even offset the increase in luminosity expected from a constant-mass model. However, this hypothesis is challenging to test. Here, we propose a novel observational proxy of the Sun's ancient mass that may be readily measured from accumulation patterns in sedimentary rocks on Earth and Mars. We show that the orbital parameters of the Solar system planets undergo quasi-cyclic oscillations at a frequency, given by secular mode g_2-g_5, that scales approximately linearly with the Sun's mass. Thus by examining the cadence of sediment accumulation in ancient basins, it is possible distinguish between the cases of a constant mass Sun and a more massive ancient Sun to a precision of greater than about 1 per cent. This approach provides an avenue toward verification, or of falsification, of the massive early Sun hypothesis.Comment: 7 pages, 4 Figures. Accepted to The Astrophysical Journal Letter

Where is the Learning in Smaller Learning Communities? Academic Press, Social Support for Learning, and Academic Engagement in Smaller Learning Community Classrooms

The extent to which Academic Press and strong social relationships impact Academic Engagement in smaller learning communities (SLCs) situated in large comprehensive urban high schools was investigated. Data were collected through classroom observations, student questionnaires and focus groups with teachers and analyzed using descriptive statistics, multivariate analysis of variance (MANOVA), and content analysis of focus interview transcripts. Findings from the survey data confirm those found in much of the existing literature, namely that students experiencing high levels of Academic Press were more often the most academically engaged. This finding was also confirmed for African American students in high Academic Press math classes. Social Support for Learning was not confirmed as a key factor in Academic Engagement. Descriptive statistics indicated moderate to low levels of Academic Press, Social Support for Learning and Academic Engagement in student self report data and in classroom observations. Results from focus groups of teachers participating in smaller learning communities identified themes suggesting that much of the Academic Press and Social Support for Learning evident in the SLCs examined was attributable to the individual efforts of teachers, sometimes in spite of the SLC structure. Additionally, factors impacting engagement emerged, chief among them being teacher and student rapport and the relevance and complexity of the curriculum. Implications for future practice and directions for further research are also discussed

Nontraumatic Dental Condition-related Visits to Emergency Departments on Weekdays, Weekends and Night Hours: Findings from the National Hospital Ambulatory Medical Care Survey

Objective: To determine whether the rates of nontraumatic dental condition (NTDC)-related emergency department (ED) visits are higher during the typical working hours of dental offices and lower during night hours, as well as the associated factors. Methods: We analyzed data from the National Hospital Ambulatory Medical Care Survey for 1997 through 2007 using multivariate binary and polytomous logistic regression adjusted for survey design to determine the effect of predictors on specified outcome variables. Results: Overall, 4,726 observations representing 16.4 million NTDC-related ED visits were identified. Significant differences in rates of NTDC-related ED visits were observed with 40%–50% higher rates during non-working hours and 20% higher rates on weekends than the overall average rate of 170 visits per hour. Compared with 19–33 year olds, subjects [relative rate ratio (RRR) = 1.6 to 1.8], whereas those aged 73 and older had lower relative rates during nonworking hours (RRR = 0.4; overall P = 0.0005). Compared with those having private insurance, Medicaid and self-pay patients had significantly lower relative rates of NTDC visits during nonworking and night hours (RRR = 0.6 to 0.7, overall P \u3c 0.0003). Patients with a dental reason for visit were overrepresented during the night hours (RRR = 1.3; overall P = 0.04). Conclusion: NTDC-related visits to ED occurred at a higher rate during non-working hours and on weekends and were significantly associated with age, patient-stated reason for visit and payer type

A shorter Archean day-length biases interpretations of the early Earth's climate

Earth's earliest sedimentary record contains evidence that surface temperatures were similar to, or perhaps even warmer than modern. In contrast, standard Solar models suggest the Sun was 25% less luminous at this ancient epoch, implying a cold, frozen planet-all else kept equal. This discrepancy, known as the Faint Young Sun Paradox, remains unresolved. Most proposed solutions invoke high concentrations of greenhouse gases in the early atmosphere to offset for the fainter Sun, though current geological constraints are insufficient to verify or falsify these scenarios. In this work, we examined several simple mechanisms that involve the role played by Earth's spin rate, which was significantly faster during Archean time. This faster spin rate enhances the equator-to-pole temperature gradient, facilitating a warm equator, while maintaining cold poles. Results show that such an enhanced meridional gradient augments the meridional gradient in carbonate deposition, which biases the surviving geological record away from the global mean, toward warmer waters. Moreover, using simple atmospheric models, we found that the faster-spinning Earth was less sensitive to ice-albedo feedbacks, facilitating larger meridional temperature gradients before succumbing to global glaciation. We show that within the faster-spinning regime, the greenhouse warming required to generate an ice-free Earth can differ from that required to generate an Earth with permanent ice caps by the equivalent of 1-2 orders of magnitude of pCO2. Accordingly, the resolution of the Faint Young Sun problem depends significantly on whether the early Earth was ever, or even at times, ice-free.Comment: 15 pages. 7 Figures. Accepted for publication in Earth and Planetary Science Letter

A shorter Archean day-length biases interpretations of the early Earth's climate

Earth's earliest sedimentary record contains evidence that surface temperatures were similar to, or perhaps even warmer than modern. In contrast, standard Solar models suggest the Sun was 25% less luminous at this ancient epoch, implying a cold, frozen planet—all else kept equal. This discrepancy, known as the Faint Young Sun Paradox, remains unresolved. Most proposed solutions invoke high concentrations of greenhouse gases in the early atmosphere to offset for the fainter Sun, though current geological constraints are insufficient to verify or falsify these scenarios. In this work, we examined several simple mechanisms that involve the role played by Earth's spin rate, which was significantly faster during Archean time. This faster spin rate enhances the equator-to-pole temperature gradient, facilitating a warm equator, while maintaining cold poles. Results show that such an enhanced meridional gradient augments the meridional gradient in carbonate deposition, which biases the surviving geological record away from the global mean, toward warmer waters. Moreover, using simple atmospheric models, we found that the faster-spinning Earth was less sensitive to ice-albedo feedbacks, facilitating larger meridional temperature gradients before succumbing to global glaciation. We show that within the faster-spinning regime, the greenhouse warming required to generate an ice-free Earth can differ from that required to generate an Earth with permanent ice caps by the equivalent of 1–2 orders of magnitude of pCO_2. Accordingly, the resolution of the Faint Young Sun problem depends significantly on whether the early Earth was ever, or even at times, ice-free