Current fossil, genetic, and archeological data indicate that Homo sapiens originated in Africa in the late Middle Pleistocene. By the end of the Late Pleistocene, our species was distributed across every continent except Antarctica, setting the foundations for the subsequent demographic and cultural changes of the Holocene. The intervening processes remain intensely debated and a key theme in hominin evolutionary studies. We review archeological, fossil, environmental, and genetic data to evaluate the current state of knowledge on the dispersal of Homo sapiens out of Africa. The emerging picture of the dispersal process suggests dynamic behavioral variability, complex interactions between populations, and an intricate genetic and cultural legacy. This evolutionary and historical complexity challenges simple narratives and suggests that hybrid models and the testing of explicit hypotheses are required to understand the expansion of Homo sapiens into Eurasia.

The role of coastal regions and coastlines in the dispersal of human populations from Africa and across the globe has been highlighted by the recent polarisation between coastal and interior models. The debate has been clouded by the use of the single term 'coastal dispersal' to embrace what is in fact a wide spectrum of possibilities, ranging from seafaring populations who spend most of their time at sea living off marine resources, to land-based populations in coastal regions with little or no reliance on marine foods. An additional complicating factor is the fact of Pleistocene and early Holocene sea-level change, which exposed an extensive coastal region that is now submerged, and may have afforded very different conditions from the modern coastal environment. We examine these factors in the Arabian context and use the term 'Blue' to draw attention to the fertile coastal rim of the Arabian Peninsula, and to the now submerged offshore landscape, which is especially extensive in some regions. We further emphasise that the attractions of the coastal rim are a product of two quite different factors, ecological diversity and abundant water on land, which have created persistently 'Green' conditions throughout the vagaries of Pleistocene climate change in some coastal regions, especially along parts of the western Arabian escarpment, and potentially productive marine environments around its coastline, which include some of the most fertile in the world.We examine the interplay of these factors in the Southwest region of Saudi Arabia and the southern Red Sea, and summarise some of the results of recent DISPERSE field investigations, including survey for Palaeolithic sites on the mainland, and underwater survey of the continental shelf in the vicinity of the Farasan Islands.We conclude that coastlines are neither uniformly attractive nor uniformly marginal to human dispersal, that they offer diverse opportunities that were spatially and temporally variable at scales from the local to the continental, and that investigating Blue Arabia in relation to its episodically Green interior is a key factor in the fuller understanding of longterm human population dynamics within Arabia and their global implications.2

Why did humans walk upright? Previous models based on adaptations to forest or savannah are challenged here in favour of physical incentives presented by steep rugged terrain—the kind of tectonically varied landscape that has produced early hominin remains. “Scrambler man” pursued his prey up hill and down dale and in so doing became that agile, sprinting, enduring, grasping, jumping two-legged athlete that we know today.

Abstract. Twitter is an established social media platform valued by scholars as an open way to disseminate scientific information and to publicly discuss research results. Scientific discussions on Twitter are viewed by the media, who can then pass on information to the wider public. Social media is used widely by geoscientists, but there is little documentation currently available regarding the benefits or limitations of this for the scientist or the public. Here, we use the example of two 2018 earthquake-related events that were widely commented on by geoscientists on Twitter: the Palu Mw 7.5 earthquake and related tsunami in Indonesia and the long-duration Mayotte island seismovolcanic crisis in the Indian Ocean. We built our study on a content and contextual analysis of selected Twitter threads about the geophysical characteristics of these events. From the analysis of these two examples, we show that Twitter promotes a very rapid building of knowledge in the minutes to hours and days following an event via an efficient exchange of information and active discussion between the scientists themselves and the public. We discuss the advantages and potential pitfalls of this relatively novel way of making scientific information accessible to scholarly peers and lay people. We argue that scientific discussion on Twitter breaks down the traditional “ivory tower” of academia, contributes to the growing trend towards open science, and may help people to understand how science is developed and, in turn, to better understand the risks related to natural/environmental hazards.

In most fault systems the direction of the relative plate motion is oblique to the azimuth of the existing faults. Hence, during earthquakes the displacement may be partitioned between several faults that accommodate different components of the total motion. Here, we quantify the effect of the obliquity of the fault system relatively to the plate-motion direction on the distribution of the deformation in the fault system, during distinct periods of the seismic cycle. The 2002 November, M w 7.9, Denali strike-slip earthquake ruptured 341 km of the Denali fault. The azimuth of the fault varies by more than 50 • over the total rupture length, making the Denali fault an ideal system to test the effect of obliquity. From west to east, thrust dominates the first part of the rupture while strike-slip dominates the central and eastern sections. Using a kinematic model that considers the obliquity of the plate-motion direction relative to the local fault azimuth, we explored how much of the far-field tectonic loading is accommodated on the main strike-slip fault during the earthquake, and how much is accommodated by distributed deformation off the main fault, on secondary structures. Using a dataset of 735 focal mechanisms, we represent the deformation using strain rosettes and we compare seismological data with model results using the areal strain. Then we developed the parameter Ca, the coefficient of accommodation, which allows a direct quantification of the efficiency of a fault to accommodate oblique motion. Using these indicators, we show that in oblique setting, such as in the Denali case, the aftershocks and the background seismicity are organized to accommodate a significant part of the deformation that is not taken on the Denali strike-slip fault during the main earthquakes. The westward increase of the obliquity actually increases the amount of such deformation accommodated through distributed thrust faults, leading to the westward widening of the Alaska Range, located north of the Denali fault. Therefore, the strain partitioning between localized slip on pre-established major faults and distributed deformation accommodated through aftershocks and background seismicity on smaller faults (highlighted here by the longer-term topography) seems to be needed during the seismic cycle to accommodate the boundary conditions in such oblique settings.

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Abstract. Twitter is an established social media platform valued by scholars as an open way to disseminate scientific information and to publicly discuss research results. Scientific discussions are widely viewed by the media who can then pass on information to the wider public. Here, we take the example of two 2018 earthquake-related events which were widely commented on Twitter by geoscientists: the Palu Mw 7.5 earthquake and tsunami in Indonesia and the long-duration Mayotte island seismo-volcanic crisis. We build our study on a content and contextual analysis of selected Twitter threads about the geophysical characteristics of these events. From the analysis of these two examples, we show that Twitter promotes very rapid building of knowledge – in the minutes to hours and days following an event – via an efficient exchange of information and active discussion between the scientists themselves and with the public. We discuss the advantages and potential pitfalls of this relatively novel way to make scientific information accessible to scholarly peers and to lay people. We argue that scientific discussion on Twitter breaks down the traditional ivory towers of academia, following growing trends towards open science, and may help people to understand how science is developed, and, in the case of natural/environmental hazards, to better understand their risks.