LIPs, orogens and supercontinents: The ongoing saga

Of nine large age peaks in zircon and LIP time series <2300 Ma (2150, 1850, 1450, 1400, 1050, 800, 600, 250 and 100 Ma), only four are geographically widespread (1850, 1400, 800 and 250 Ma). These peaks occur both before and after the onset of the supercontinent cycle, and during both assembly and breakup phases of supercontinents. During supercontinent breakup, LIP activity is followed by ocean-basin opening in some areas, but not in other areas. This suggests that mantle plumes are not necessary for ocean-basin opening, and that LIPs should not be used to predict the timing and location of supercontinent breakups. LIP events may be produced directly by mantle plumes or indirectly from subduction regimes that have inherited mantle-cycle signatures from plume activity. A combination of variable plume event intensity and multiple plume cyclicities best explains differences in LIP age peak amplitudes and irregularities. Peaks in orogen frequency at 1850, 1050, 600 Ma, which approximately coincide with major zircon and LIP age peaks, correspond to onsets of supercontinent assembly, and age peaks at 1450, 250 and 100 Ma correspond to supercontinent stasis or breakup. Although collisional orogens are more frequent during supercontinent assemblies, accretionary orogens have no preference for either breakup or assembly phases of supercontinents. A sparsity of orogens during Rodinia assembly may be related to incomplete breakup of Nuna as well as to the fact that some continental cratons never accreted to Rodinia. There are three groups of passive margins, each group showing a decrease in duration with time: Group 1 with onsets at 2.2–2.0 Ga correspond to the breakup of Neoarchean supercratons; Group 2 with onsets at 1.5–1.2 Ga correspond to the breakup of Nuna; and Group 3 with onsets at 1.5–0.1 Ga not corresponding to any particular supercontinent breakup. New paleogeographic reconstructions of supercontinents indicate that in the last 2 Gyr average angular plate speeds have not changed or have decreased with time, whereas the number of orogens has increased. A possible explanation for decreasing or steady plate speed is an increasing proportion of continental crust on plates as juvenile continental crust continued to be added in post-Archean accretionary orogens. Cycles of mantle events are now well established at 90 and 400 Myr. Significant age peaks in orogen frequency, average plate speed, LIPs and detrital zircons may be part of a 400-Myr mantle cycle, and major age peaks in the cycle occur near the onset of supercontinent assemblies. The 400-Myr cycle may have begun with a “big bang” at the 2700 Ma, although the LIP age spectrum suggests the cycle may go back to at least 3850 Ma. Large age peaks at 1850, 1050, 600 and 250 Ma may be related to slab avalanches from the mantle transition zone that occur in response to supercontinent breakups

Early human settlement of Sahul was not an accident

The first peopling of Sahul (Australia, New Guinea and the Aru Islands joined at lower sea levels) by anatomically modern humans required multiple maritime crossings through Wallacea, with at least one approaching 100 km. Whether these crossings were accidental or intentional is unknown. Using coastal-viewshed analysis and ocean drift modelling combined with population projections, we show that the probability of randomly reaching Sahul by any route is <5% until ≥40 adults are 'washed off' an island at least once every 20 years. We then demonstrate that choosing a time of departure and making minimal headway (0.5 knots) toward a destination greatly increases the likelihood of arrival. While drift modelling demonstrates the existence of 'bottleneck' crossings on all routes, arrival via New Guinea is more likely than via northwestern Australia. We conclude that anatomically modern humans had the capacity to plan and make open-sea voyages lasting several days by at least 50,000 years ago.Michael I. Bird, Scott A. Condie, Sue O’Connor, Damien O’Grady, Christian Reepmeyer, Sean Ulm, Mojca Zega, Frédérik Saltré, Corey J.A. Bradsha

Knowledge gaps in the biology, ecology, and management of the Pacific crown-of-thorns sea star, Acanthaster sp., on Australia's Great Barrier Reef

Published online 17 November 2021Crown-of-thorns sea stars (Acanthaster sp.) are among the most studied coral reef organisms, owing to their propensity to undergo major population irruptions, which contribute to significant coral loss and reef degradation throughout the Indo-Pacific. However, there are still important knowledge gaps pertaining to the biology, ecology, and management of Acanthaster sp. Renewed efforts to advance understanding and management of Pacific crown-of-thorns sea stars (Acanthaster sp.) on Australia’s Great Barrier Reef require explicit consideration of relevant and tractable knowledge gaps. Drawing on established horizon scanning methodologies, this study identified contemporary knowledge gaps by asking active and/or established crown-of-thorns sea star researchers to pose critical research questions that they believe should be addressed to improve the understanding and management of crown-of-thorns sea stars on the Great Barrier Reef. A total of 38 participants proposed 246 independent research questions, organized into 7 themes: feeding ecology, demography, distribution and abundance, predation, settlement, management, and environmental change. Questions were further assigned to 48 specific topics nested within the 7 themes. During this process, redundant questions were removed, which reduced the total number of distinct research questions to 172. Research questions posed were mostly related to themes of demography (46 questions) and management (48 questions). The dominant topics, meanwhile, were the incidence of population irruptions (16 questions), feeding ecology of larval sea stars (15 questions), effects of elevated water temperature on crown-of-thorns sea stars (13 questions), and predation on juveniles (12 questions). While the breadth of questions suggests that there is considerable research needed to improve understanding and management of crown-of-thorns sea stars on the Great Barrier Reef, the predominance of certain themes and topics suggests a major focus for new research while also providing a roadmap to guide future research efforts.Morgan S. Pratchett … Camille Mellin … et al

Draft genome sequence of chickpea (Cicer arietinum) provides a resource for trait improvement

Chickpea (Cicer arietinum) is the second most widely grown legume crop after soybean, accounting for a substantial proportion of human dietary nitrogen intake and playing a crucial role in food security in developing countries. We report the ∼738-Mb draft whole genome shotgun sequence of CDC Frontier, a kabuli chickpea variety, which contains an estimated 28,269 genes. Resequencing and analysis of 90 cultivated and wild genotypes from ten countries identifies targets of both breeding-associated genetic sweeps and breeding-associated balancing selection. Candidate genes for disease resistance and agronomic traits are highlighted, including traits that distinguish the two main market classes of cultivated chickpea—desi and kabuli. These data comprise a resource for chickpea improvement through molecular breeding and provide insights into both genome diversity and domestication