Hominin population bottleneck coincided with migration from Africa during the Early Pleistocene ice age transition.

Two recently published analyses make cases for severe bottlenecking of human populations occurring in the late Early Pleistocene, one case at about 0.9 Mya based on a genomic analysis of modern human populations and the low number of hominin sites of this age in Africa and the other at about 1.1 Mya based on an age inventory of sites of hominin presence in Eurasia. Both models point to climate change as the bottleneck trigger, albeit manifested at very different times, and have implications for human migrations as a mechanism to elude extinction at bottlenecking. Here, we assess the climatic and chronologic components of these models and suggest that the several hundred-thousand-year difference is largely an artifact of biases in the chronostratigraphic record of Eurasian hominin sites. We suggest that the best available data are consistent with the Galerian hypothesis expanded from Europe to Eurasia as a major migration pulse of fauna including hominins in the late Early Pleistocene as a consequence of the opening of land routes from Africa facilitated by a large sea level drop associated with the first major ice age of the Pleistocene and concurrent with widespread aridity across Africa that occurred during marine isotope stage 22 at ~0.9 Mya. This timing agrees with the independently dated bottleneck from genomic analysis of modern human populations and allows speculations about the relative roles of climate forcing on the survival of hominins.

Early North African Acheulean techno-economic systems at Thomas Quarry I - L1 (Casablanca, Morocco).

North Africa is a key area for understanding cultural processes that led to the Acheulean pan - African emergence and expressions and the related hominin population dynamics. Unfortunately, little is known about the early Acheulean in this vast area of the African continent due to the scarceness of archaeological sites in stratigraphic context with reliable chronometric data, human remains, and technological analyses of the lithic industries. Here, we present the first comprehensive techno-economic analysis of the early Acheulean assemblage from Thomas Quarry I - Unit L1 (ThI-L1, Casablanca, Morocco), which is the earliest Acheulean site of North Africa, unambiguously dated to 1.3 Ma. Fieldwork has unearthed faunal remains and a lithic collection containing over 3800 artefacts, which represents one of the largest series for the early African Acheulean. The assemblage is mainly composed of quartzites and to a lesser extent of silicites, both abundantly available near the site. Previously published results of the silicite study revealed two different productions for the extraction of small flakes and of bladelet-like flakes. In this work, we analyse the techno-economic systems of the quartzite assemblage. Two distinct quartzite productions co-occur, one devoted to the manufacture of Large Cutting Tools (LCTs), the other focused on the extraction of small-medium sized flakes. LCTs were usually produced from large cobbles, less often from large flakes detached mainly using the entame core method. The main technical objective was to obtain large pointed tools and, more rarely, large tools with a transversal cutting edge. Results support the existence of a strong synergy between conceptual and operational schemes regulated by the ability to anticipate the final tool morphology and to apply standardized shaping procedures to manufacture recurrent morphotypes. Quartzite small-medium sized flakes were produced by a diversity of flaking methods adapted to the cobble blank morphologies and were not retouched. The results allow to assess that the earliest technical expression of the Acheulean in North Africa is characterised by a high diversification of the stone knapping outcomes, the complexity of the mental templates, and the flexible structure of the operational schemes.

First high resolution chronostratigraphy for the early North African Acheulean at Casablanca (Morocco).

The onset of the Acheulean, marked by the emergence of large cutting tools (LCTs), is considered a major technological advance in the Early Stone Age and a key turning point in human evolution. The Acheulean originated in East Africa at ~ 1.8-1.6 Ma and is reported in South Africa between ~ 1.6 and > 1.0 Ma. The timing of its appearance and development in North Africa have been poorly known due to the near-absence of well-dated sites in reliable contexts. The ~ 1 Ma stone artefacts of Tighennif (Algeria) and Thomas Quarry I-Unit L (ThI-L) at Casablanca (Morocco) are thus far regarded as documenting the oldest Acheulean in North Africa but whatever the precision of their stratigraphical position, both deserve a better chronology. Here we provide a chronology for ThI-L, based on new magnetostratigraphic and geochemical data. Added to the existing lithostratigraphy of the Casablanca sequence, these results provide the first robust chronostratigraphic framework for the early North African Acheulean and firmly establish its emergence in this part of the continent back at least to ~ 1.3 Ma.

Equatorial convergence of India and early Cenozoic climate trends.

India's northward flight and collision with Asia was a major driver of global tectonics in the Cenozoic and, we argue, of atmospheric CO(2) concentration (pCO(2)) and thus global climate. Subduction of Tethyan oceanic crust with a carpet of carbonate-rich pelagic sediments deposited during transit beneath the high-productivity equatorial belt resulted in a component flux of CO(2) delivery to the atmosphere capable to maintain high pCO(2) levels and warm climate conditions until the decarbonation factory shut down with the collision of Greater India with Asia at the Early Eocene climatic optimum at approximately 50 Ma. At about this time, the India continent and the highly weatherable Deccan Traps drifted into the equatorial humid belt where uptake of CO(2) by efficient silicate weathering further perturbed the delicate equilibrium between CO(2) input to and removal from the atmosphere toward progressively lower pCO(2) levels, thus marking the onset of a cooling trend over the Middle and Late Eocene that some suggest triggered the rapid expansion of Antarctic ice sheets at around the Eocene-Oligocene boundary.

Mesozoic Alpine facies deposition as a result of past latitudinal plate motion.

The fragmentation of Pangaea as a consequence of the opening of the Atlantic Ocean is documented in the Alpine-Mediterranean region by the onset of widespread pelagic sedimentation. Shallow-water sediments were replaced by mainly pelagic limestones in the Early Jurassic period, radiolarian cherts in the Middle-Late Jurassic period, and again pelagic limestones in the Late Jurassic-Cretaceous period. During initial extension, basin subsidence below the carbonate compensation depth (CCD) is thought to have triggered the transition from Early Jurassic limestones to Middle-Late Jurassic radiolarites. It has been proposed that the transition from radiolarites to limestones in the Late Jurassic period was due to an increase in calcareous nannoplankton abundance when the CCD was depressed below the ocean floor. But in modern oceans, sediments below the CCD are not necessarily radiolaritic. Here we present palaeomagnetic samples from the Jurassic-Cretaceous pelagic succession exposed in the Lombardian basin, Italy. On the basis of an analysis of our palaeolatitudinal data in a broader palaeogeographic context, we propose an alternative explanation for the above facies tripartition. We suggest that the Lombardian basin drifted initially towards, and subsequently away from, a near-equatorial upwelling zone of high biosiliceous productivity. Our tectonic model for the genesis of radiolarites adds an essential horizontal plate motion component to explanations involving only vertical variations of CCD relative to the ocean floor. It may explain the deposition of radiolarites throughout the Mediterranean and Middle Eastern region during the Jurassic period.