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Homo erectusis the founding early hominin species of Island Southeast Asia, and reached Java (Indonesia) more than 1.5 million years ago1,2. Twelve H. erectuscalvaria (skull caps) and two tibiae (lower leg bones) were discovered from a bone bed located about 20 m above the Solo River at Ngandong (Central Java) between 1931 and 19333,4, and are of the youngest, most-advanced form of H. erectus5–8. Despite the importance of the Ngandong fossils, the relationship between the fossils, terrace fill and ages have been heavily debated9–14. Here, to resolve the age of the Ngandong evidence, we use Bayesian modelling of 52 radiometric age estimates to establish—to our knowledge—the first robust chronology at regional, valley and local scales. We used uranium-series dating of speleothems to constrain regional landscape evolution; luminescence, 40argon/39argon (40Ar/39Ar) and uranium-series dating to constrain the sequence of terrace evolution; and applied uranium-series and uranium series–electron-spin resonance (US–ESR) dating to non-human fossils to directly date our re-excavation of Ngandong5,15. We show that at least by 500 thousand years ago (ka) the Solo River was diverted into the Kendeng Hills, and that it formed the Solo terrace sequence between 316 and 31 ka and the Ngandong terrace between about 140 and 92 ka. Non-human fossils recovered during the re-excavation of Ngandong date to between 109 and 106 ka (uranium-series minimum)16and 134 and 118 ka (US–ESR), with modelled ages of 117 to 108 thousand years (kyr) for the H. erectusbone bed, which accumulated during flood conditions3,17. These results negate the extreme ages that have been proposed for the site and solidify Ngandong as the last known occurrence of this long-lived species.

We examined the impact of three different sample preparation methods on bulk soil geochemistry data obtained from a hand‐held, portable X‐ray fluorescence (pXRF) spectrometer. We generated data from a soil core recovered from the surface, downward into unaltered loess, and into a buried soil at a site in eastern Iowa. Samples were scanned (i) directly from field‐moist soil cores; (ii) after drying, grinding, and being loosely massed in plastic cups; and (iii) as pressed‐powder pellets. Data derived using these methods were compared with data obtained from a standard benchtop X‐ray fluorescence (XRF) unit. Generally, the results indicated that data from pressed powder pellets often provide the best correlation to benchtop XRF data, although the results were sometimes element or compound specific. Calcium oxide, Fe2O3, and K2O generally provided the strongest correlations between pXRF‐ and XRF‐reported values; SiO2data were more problematic. Field‐moist pXRF scans generally underestimated element concentrations, but the correlations between pXRF and benchtop XRF measurements were greatly improved after applying pXRF‐derived calibration standards. In summary, although element/compound data provided by pXRF showed significant relationships to benchtop XRF data, the results are improved with proper sample preparation (i.e., drying, grinding, pressing) and usually by calibrating the pXRF data against known standards.

This paper examines the coevolutionary roles of variable flow features and heterogeneous substrates on knickpoint migration. A conceptual model is used to depict distinct migration mechanisms in a channelized headwater system of a representative intensively managed watershed in the Deep Loess Region of the U.S. Midwest. Throughout this region, entrenched streams have eroded into alluvial‐based strata that are horizontally consistent but vertically heterogeneous. Variable flow in these streams switches between vented conditions, where water shoots from the knickpoint face as an aerated plunging jet, and unvented conditions, where water clings close to its face through suction. These switches affect hydrodynamic mechanisms controlling migration but cannot explain fully observed alternating slow‐fast migration rates. It is hypothesized that vertically heterogeneous strata in entrenched streams, specifically strong‐over‐weak layers, facilitate observed changes in knickpoint migration rates. Preferential erosion of weaker sublayers is thought to trigger other erosional mechanisms to accelerate migration even at low flows. Herein, a migration “diary” documents a representative knickpoint's displacement over time with flow measurements and site stratigraphy. Slower migration occurred from 2006 to 2009 through fluvial erosion of a resistant silt loam cap. From 2009 to 2012, migration accelerated as the knickpoint face reached a critical height through scour. A flow back roller formed, which preferentially eroded a weaker sand sublayer. Undercutting/cantilever failure cycles persisted, causing 30 m of retreat within 2 months (i.e., 62.5% of the total migration over 78 months). Comparisons with established fluvial hydraulics‐based and undercutting/cantilever‐based migration models confirm the hypothesis and importance of both stratified substrates and hydrodynamic controls on knickpoint migration. A conceptual sketch is used to depict distinct knickpoint migration mechanisms in a channelized semicohesive streamKnickpoint migration in semicohesive streams is governed by coplay of flow and stratigraphic controls that can change in space and timeHeterogeneity in substrate properties can lead to preferential erosion of material, controlling the mechanisms that drive the migration

ABSTRACTThis study investigated students' attitudes, engagement, satisfaction, and performance in Introduction to Environmental Science after it was transformed from a typical large lecture to a student-centered learning environment. The instructors of the course collaborated with the Office of Teaching, Learning & Technology and radically redesigned the course by adopting evidence-based pedagogical methods and instructional technology to offer a rich active learning environment. Students' engagement, satisfaction, and performance in the transformed course were compared to the students in the same course that was traditionally taught in a previous semester in order to measure the effect of the transformed course on student learning. Four self-reported surveys and a focus group interview were administered during the semester, and performance scores, prior learning data, and demographic information were collected at the end of the semester. The assessment results indicate that the students in the transformed course prepared for the class significantly more, engaged in the course significantly better, and were significantly more satisfied with the course than were the students in the traditional lecture-format course. Most of all, multiple linear regression indicates that the students in the transformed course earned, on average, about three-fourths of a letter grade higher on their final grade after controlling for cumulative grade point average. The students in the transformed course reported that online learning materials and frequent formative assessments using online quizzes were helpful in their learning, and they perceived the course was relevant to real-world applications that matter to their daily life.

Patterns of erosion and deposition act as a filter that strongly influences the disposition of the archaeological record of the Central and Eastern Plains of the North American Midcontinent. Detailed studies of alluvial valley stratigraphy in four drainage basins in the region reveal temporal and spatial patterns of fluvial system behavior that control the preservation and visibility of past human activity. These basins are located on a 600-km-long longitudinal gradient extending from semiarid southwestern Kansas to moist-subhumid central Iowa. Despite significant environmental variability along this transect, basin-wide patterns of Holocene erosion and deposition are similar across the study area. From ca. 11,000 to 8000 yr B.P., aggradation, punctuated by slow alluviation and/or stability around 10,000 yr B.P., was the dominant process in large and some small valleys. The early and middle Holocene (ca. 8000–5000 yr B.P.) was a period of net erosion and sediment movement in small valleys, sediment storage in large valleys, and episodic aggradation on alluvial fans. During the late Holocene (post-5000 yr B.P.), alluvial fans stabilized, small valleys became zones of net sediment storage, and aggradation slowed in large valleys. Basin-wide aggradation followed by entrenchment and channel migration characterizes fluvial activity during the Historic period. Consideration of the effects of these temporal and spatial patterns of Holocene erosion and alluviation on the archaeological record is crucial for developing efficient cultural resource sampling strategies and for accurately interpreting the archaeological record. © 2002 John Wiley & Sons, Inc.