Gravel-bedded streams are thought to have a characteristic meandering form bordered by a self-formed, fine-grained floodplain. This ideal guides a multibillion-dollar stream restoration industry. We have mapped and dated many of the deposits along mid-Atlantic streams that formed the basis for this widely accepted model. These data, as well as historical maps and records, show instead that before European settlement, the streams were small anabranching channels within extensive vegetated wetlands that accumulated little sediment but stored substantial organic carbon. Subsequently, 1 to 5 meters of slackwater sedimentation, behind tens of thousands of 17th- to 19th-century milldams, buried the presettlement wetlands with fine sediment. These findings show that most floodplains along mid-Atlantic streams are actually fill terraces, and historically incised channels are not natural archetypes for meandering streams.

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Few constraints on the timing, amount and distribution of lithospheric extension associated with flood-basalt magmatism were available from the southern Main Ethiopian rift system, where the base of the Cenozoic volcanic succession is exposed by faulting. New structural observations, together with K–Ar and 40 Ar/ 39 Ar geochronology data from a transect of the Chamo basin–Amaro horst–Galana basin, show that basins are bounded by faults with steep dips at the surface, and the stratal dips of Eocene–Recent volcanic and sedimentary units are generally less than 20°. Little or no extension accompanied the extrusion of a 0.5 to 1 km thick sequence of transitional tholeiitic flood basalts between 45 and 35 Ma. Stratigraphical correlations with basins to the north and southwest suggest that felsic eruption(s) at c. 37 Ma blanketed much of the southern Ethiopian plateau region with a felsic tuff unit. A second, less widespread, episode of alkali basalt and trachyte volcanism occurred between 18 and 11 Ma, and Recent alkali basalt volcanism occurs within the Chamo basin. The attitude, distribution, and diversity of Neo–gene–Recent volcanic and sedimentary strata within the Chamo and Galana basins indicate that crustal extension, basin subsidence, and rift flank uplift began during or after the second flood-basalt phase. Based on cross-sectional reconstruction to the top of the Oligocene tuff, we estimate a minimum of 12 km crustal extension (β ≈ 1.12), and infer that maximum extension across the southern Ethiopian rift is less than 25 km. Extension is primarily accommodated by slip along the border faults bounding the asymmetric basins, with small amounts of extension occurring within the hanging walls. Crude estimates of original basalt layer thickness prior to erosion in the Amaro region suggest that roughly comparable volumes of basaltic material erupted during the two episodes of flood-basalt magmatism (45–35 Ma and 18–11 Ma). The small amounts of lithospheric extension and the large volumes of magma estimated in this study of the southern Main Ethiopian rift suggest a very hot plume and/or efficient thinning of the mantle lithosphere from below by mantle plume processes during the two discrete episodes of flood-basalt volcanism.

The geographical origin of modern humans is the subject of ongoing scientific debate. The 'multiregional evolution' hypothesis argues that modern humans evolved semi-independently in Europe, Asia and Africa between 100,000 and 40,000 years ago, whereas the 'out of Africa' hypothesis contends that modern humans evolved in Africa between 200 and 100 kyr ago, migrating to Eurasia at some later time. Direct palaeontological, archaeological and biological evidence is necessary to resolve this debate. Here we report the discovery of early Middle Stone Age artefacts in an emerged reef terrace on the Red Sea coast of Eritrea, which we date to the last interglacial (about 125 kyr ago) using U-Th mass spectrometry techniques on fossil corals. The geological setting of these artefacts shows that early humans occupied coastal areas and exploited near-shore marine food resources in East Africa by this time. Together with similar, tentatively dated discoveries from South Africa this is the earliest well-dated evidence for human adaptation to a coastal marine environment, heralding an expansion in the range and complexity of human behaviour from one end of Africa to the other. This new, wide-spread adaptive strategy may, in part, signal the onset of modern human behaviour, which supports an African origin for modern humans by 125 kyr ago.

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