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Sterkfontein is the most prolific single source of

Cosmogenic radionuclides (CRNs) are the standard tool to derive centennial-to-millennial timescale denudation rates; however, it has been demonstrated that chemical weathering in some settings can bias CRNs as a proxy for landscape denudation. Currently, studies investigating CRN weathering biases have mostly focused on the largely insoluble target mineral quartz in felsic lithologies. Here, we examine the response of CRN build-up for both soluble and insoluble target minerals under different weathering scenarios. We assume a simple box model in which bedrock is converted to a well-mixed regolith at a constant rate, and denudation occurs by regolith erosion and weathering either in the regolith or along the regolith–bedrock interface, as is common in carbonate bedrock. We show that weathering along the regolith–bedrock interface increases CRN concentrations compared to a no-weathering case and how independently derived weathering rates or degrees can be used to correct for this bias. If weathering is concentrated within the regolith, insoluble target minerals will have a longer regolith residence time and higher nuclide concentration than soluble target minerals. This bias can be identified and corrected using paired-nuclide measurements of minerals with different solubility coupled with knowledge of either the bedrock or regolith mineralogy to derive denudation and long-term weathering rates. Similarly, single-nuclide measurements on soluble or insoluble minerals can be corrected to determine denudation rates if a weathering rate and compositional data are available. Our model highlights that for soluble target minerals, the relationship between nuclide accumulation and denudation is not monotonic. We use this understanding to map the conditions of regolith mass, weathering, and denudation rates at which weathering corrections for cosmogenic nuclides become large and ambiguous, as well as identify environments in which the bias is mostly negligible and CRN concentrations reliably reflect landscape denudation. We highlight how measurements of CRNs from soluble target minerals, coupled with bedrock and regolith mineralogy, can help to expand the range of landscapes for which centennial-to-millennial timescale denudation and weathering rates can be obtained.

The Early Pleistocene site of Swartkrans in South Africa's Cradle of Humankind World Heritage Site has been significant for our understanding of the evolution of both early Homo and Paranthropus, as well as the earliest archaeology of southern Africa. Previous attempts to improve a faunal age estimate of the earliest deposit, Member 1, had produced results obtained with uranium-lead dating (U-Pb) on flowstones and cosmogenic burial dating of quartz, which placed the entire member in the range of1.7/1.8 Ma and2.3 Ma. In 2014, two simple burial dates for the Lower Bank, the earliest unit within Member 1, narrowed its age to between ca. 1.8 Ma and 2.2 Ma. A new dating program using the isochron method for burial dating has established an absolute age of 2.22 ± 0.09 Ma for a large portion of the Lower Bank, which can now be identified as containing the earliest Oldowan stone tools and fossils of Paranthropus robustus in South Africa. This date agrees within one sigma with the U-Pb age of 2.25 ± 0.08 Ma previously published for the flowstone underlying the Lower Bank and confirms a relatively rapid rate of accumulation for a large portion of the talus.

We present a new calibration of the in-situ production rate of cosmogenic 36Cl from Fe with the aim of enabling the use of Fe-oxides and other Fe-rich minerals as 36Cl target materials. The calibration was conducted using magnetite mineral separates from rocks with well-constrained exposure histories, including late-Pleistocene glacial erratic boulders from the Sierra Nevada, California, USA and samples from a slowly eroding ridgetop in the Quadrilatero Ferrifero, Minas Gerais, Brazil. At both sites the 36Cl production rate from Fe was calibrated against the production rate of 10Be in co-occurring quartz, while in the Sierra Nevada the calibration was also conducted against 14C-based deglaciation ages. The data produce a mean 36ClFe to 10BeQtz production ratio of 0.417 ± 0.010 at the calibration sites. This ratio may depend on altitude and latitude. A reaction-specific scaling model predicts that the calibrated ratio scales to a reference value at sea level and high latitude of 0.326 ± 0.008. When considering uncertainties in reference 10Be production rate, this is equivalent to a sea level and high latitude production rate of 1.28 ± 0.11 atoms g Fe−1 yr−1. Additional data are needed to confirm the scaling behavior.

The Rietputs 15 site near Windsorton (Northern Cape, South Africa) has recently gained attention as the first Early Acheulean site in South Africa to be dated with an absolute rather than relative method (Gibbon et al., 2009). A large assemblage from Pit 5 has a cosmogenic nuclide burial age of 1.31 ± 0.21 Ma. In addition to the Early Acheulean handaxes, cleavers and picks retrieved from this pit, a notable feature is the presence of an organised core flaking strategy, which contrasts with the simpler reduction methods that dominate the assemblage. Just over 17% of the cores display features that demonstrate hominids were able to control core working in order to exploit the largest surface, occasionally for a preferential removal. The most common form of organised core has an asymmetrical shape, in which the underside is worked pyramidally to produce a larger upper surface suitable for yielding sizeable flakes, and in the most developed form flakes are removed perpendicular to the surface. Limited platform working of these cores suggests that raw materials were intentionally selected for large surfaces and shapes appropriate for organised flaking. Hornfels comprises over 64% of the raw materials, which is unusual in the African earlier Acheulean. Rietputs 15 provides strong supporting evidence for the origins of organised flaking strategies during the course of the Early Acheulean.

Application of meteoric 10Be inventories and 10Be/9Be ratios to determine surface ages, erosion rates, and denudation rates requires understanding the conditions under which meteoric 10Be functions as an open vs. closed system near the Earth's surface. Here, we investigate biologically mediated beryllium isotope mobility in an oak-hickory forest in eastern North America. We report meteoric 10Be and 9Be concentrations in soils, roots, and leaves of four deciduous tree species. The data show that beryllium is readily taken-up from the soil by roots, cycled through leaves, and redeposited on the forest floor with autumn leaf abscission. Hickory (genus Carya) dominates beryllium cycling with a spatially averaged annual 10Be flux to the soil surface through litterfall that is four times higher than the atmospheric 10Be deposition rate. Biocycling may thus modulate the shape of meteoric 10Be concentration and 10Be/9Be ratio depth profiles in soils. We present a biocycling model that describes beryllium uptake by roots, redeposition on the surface through litterfall, and retention according to an exponential adsorption rule. This model reproduces the observed form of meteoric 10Be and 9Be depth profiles and the beryllium isotope ratio in foliage at the study site. The model also indicates that both declining and bulge-type meteoric 10Be depth profiles may result from biocycling, even where beryllium loss by leaching is significant, implying that declining meteoric 10Be depth profiles may not be indicative of quantitative 10Be retention. We recommend that biocycling be considered in models of beryllium isotope systematics where hickory or other beryllium accumulating taxa are present and where litter production rates are high.

The site of Gongwangling is among the most important early hominin sites in China due to the discovery of a partial Homo erectus cranium. Until recently the cranium has been widely accepted as ∼1.15 Ma (million years) in age based on magnetostratigraphy and loess/paleosol correlation. However, a revised magnetostratigraphic and pedostratigraphic study assigned a much older age of 1.63 Ma, making Gongwangling the second oldest hominin cranium-bearing site in Eurasia. Here we apply the isochron burial dating method as an independent check for the magnetostratigraphy. Samples from the top of a gravel bed ∼7 m below the fossil-bearing layer give an isochron burial age of 1.82 ± 0.12 Ma, in excellent agreement with the Olduvai subchron in the revised magnetostratigraphy, supporting the antiquity of the cranium.

The thick alluvial conglomerate sequences around the Tibetan Plateau have been notoriously difficult to date. Here we use the cosmogenic nuclide burial dating method to date the Yumen and Jiuquan formations, a ∼900 m thick fanglomerate found in the Hexi Corridor, the foredeep of the Qilian Shan, and exposed in the Laojunmiao anticline. We date 16 sites with simple burial dating and 2 sites with isochron burial dating, and use these dates to reinterpret the magnetostratigraphy of the section. We suggest that the bottom of the Yumen Formation, defined by a progressive unconformity, is around 5 My. Taking this timing as the initiation of anticline growth, the long-term crustal shortening rate at the ramp zone in western Qilian Shan is about 0.72 mm/yr, consistent with those obtained from middle and eastern Qilian Shan. The boundary between the Yumen and Jiuquan Formations is near ∼1.2 My. Three other angular unconformities are dated to ∼2.6–3.1, ∼2.2–2.5, and ∼1.2–1.7 My, respectively. Burial dating offers a robust chronology for these deposits, and when combined with paleomagnetic stratigraphy offers much tighter precision.

Climate regulation of erosion in unglaciated landscapes remains difficult to decipher. While climate may disrupt process feedbacks that would otherwise steer landscapes toward steady erosion, sediment transport processes tend to erase past climate landforms and thus bias landscape evolution interpretations. Here, we couple a 50 k.y. paleoenvironmental record with 24 10Be-derived paleo-erosion rates from a 63-m-thick sediment archive in the unglaciated soil-mantled Oregon Coast Range. Our results span the forested marine oxygen isotope stage (MIS) 3 (50–29 ka), the subalpine MIS 2 (29–14 ka), and the forested MIS 1 (14 ka to present). From 46 ka through 28.5 ka, erosion rates increased from 0.06 mm yr–1 to 0.23 mm yr–1, coincident with declining temperatures. Mean MIS 2 erosion rates remained at 0.21 mm yr–1 and declined with increasing MIS 1 temperatures to the modern mean rate of 0.08 mm yr–1. Paleoclimate reconstructions and a frost-weathering model suggest periglacial processes were vigorous between 35 and 17 ka. While steady erosion is often assumed, our results suggest that climate strongly modulates soil production and transport on glacial-interglacial time scales. By applying a cosmogenic paleo-erosion model to evaluate 10Be concentrations in our sedimentary archive, we demonstrate that the depth of soil mixing (which is climate-dependent) controls the lag time required for cosmogenic erosion rates to track actual values. Our results challenge the widely held assumption that climate has minimal impact on erosion rates in unglaciated midlatitude terrain, which invites reconsideration of the extent to which past climate regimes manifest in modern landscapes.

The Yiyuan hominin fossil site is one of the few localities in China where a partial skullcap and several loose teeth of Homo erectus have been discovered. Yiyuan was previously assigned broadly to the Middle Pleistocene by biostratigraphical correlation and ESR/U-series dating. Here, we report the first application of a radio-isotopic dating method to the site. 26Al/10Be burial dating results derived from two sand samples from the fossiliferous deposits show that the hominin fossils can be confidently dated to 0.64 ± 0.08 Ma (million years ago). The reliability of this age is supported by the zero age of modern fluvial sediment near the cave. Our result is consistent with the age estimation based on biostratigraphic correlation and supports the argument that the Yiyuan and Zhoukoudian Locality 1 H. erectus fossils are contemporaneous. The results presented here, along with other recent chronological studies on Chinese Middle Pleistocene hominin sites, indicate that the time span from 600–400 ka (thousand years ago) is a critical period for human evolution in East Asia. Importantly, this time bracket includes several major climatic changes that would have influenced hominins, both morphologically and behaviorally.

Drainage divide migration is of wide interest because it drives changes in topography, aquatic species habitat, and fluxes of water and nutrients across Earth's surface. To date, divide migration rates have been measured in relatively few places, partly because of the rarity of denudation rate measurements on opposing sides of drainage divides. Here we report 54 basin-averaged denudation rates across the Qilian Shan, China, inferred from 10Be concentrations in stream-borne quartz. We combine these with 18 previously published basin-averaged denudation rates and new measurements of the topographic metric χ in the river networks. These data reveal divide migration rates of ∼3–1385 mm kyr−1 and area loss in the headwater reach of the Hei River basin. Cross-divide differences in denudation rate (ΔE) and channel-head χ values (Δχ) follow an exponential relationship Δ E = Δ E 0 e − b Δ χ , providing empirical support for the hypothesis that Δχ values can reflect ΔE. Here, b has the same value within uncertainty as in ΔE-Δχ data in the southern Appalachians and the Ozark Dome in previous studies, consistent with a common set of processes controlling divide migration in all three regions. The value of Δ E 0 is 1-2 orders of magnitude higher at Qilian Shan than at the two other sites, implying higher values of ΔE at a given Δχ. Our numerical simulations show that near-exponential ΔE-Δχ relationships can arise as topographic divides approach equilibrium under spatially uniform uplift rate, consistent with divide migration toward steady state in each of these regions. Further, they show that the magnitude of ΔE at a given Δχ increases linearly with rock uplift rate. Together, these results suggest that ln(ΔE) exhibits the same sensitivity to Δχ across mountain ranges, and that the magnitude of ΔE may be strongly sensitive to rock uplift rate.

The Upland Complex is a widespread terrace of the ancestral Mississippi River. It has played a central role in studies of the Pliocene Mississippi River drainage, as well as uplift and seismicity in the central Mississippi River Valley. Previous efforts to date the Upland Complex have yielded a range of age estimates spanning the Miocene through Pleistocene. We dated gravels and Fe-oxide cements from quarries of the Upland Complex in Arkansas, Kentucky, Mississippi, and Tennessee using 26Al/10Be burial dating and (U-Th)/He geochronology. Our 26Al/10Be burial dates revealed possible Pliocene-to-Pleistocene depositional ages, while (U-Th)/He dating showed that the onset of weathering dates to at least the Pliocene. Taken together, the 26Al/10Be and (U-Th)/He age constraints demonstrate that the Upland Complex is at least Pliocene in age, and likely formed during a prolonged period of base level stability that preceded Pleistocene glaciations.

The mainstream school of human evolution posits that Homo erectus was the earliest species to leave Africa at ∼1.85 million years (Ma) ago. Recent discoveries from the Shangchen loess-palaeosol sequence near the Lantian hominid site in northern China, however, show lithic artifacts up to 2.12 Ma, pre-dating the fossil record of H. erectus. Here we apply the recently established isochron 26Al/10Be burial dating, whose reliability has been verified by intercomparison with 40Ar/39Ar dating, to two locations at the Palaeolithic site of Xihoudu ∼100 km east of Shangchen. The results show that the stone tools found within river gravels there are 2.43 ± 0.06 Ma (1σ) old, making them the earliest radio-isotopically dated evidence for human occupation in Eurasia. The new date is supported by relative dating of the associated fauna, by consistent simple burial ages of quartz sand from deep cores, and by agreement between the two isochrons. Although the validity of the Xihoudu artifacts has been previously debated because of marked fluvial abrasion, there is clear evidence of intentional flaking. In particular, in addition to two cores with small amounts of cortex, a number of flakes lack original rock cortex, which indicate multiple and sustained removals that do not occur naturally. The great antiquity of the Xihoudu artifacts renders firm support to an earlier “Out of Africa I” that approaches the emergence of the genus Homo and the Oldowan industry.

Flood control initiates Chinese civilization Around four millennia ago, Emperor Yu the Great succeeded in controlling a huge flood in the Yellow River basin. This is considered to have led to the establishment of the Xia dynasty and the start of Chinese civilization. However, the dates of the events and the links between them have remained uncertain and controversial. Using stratigraphic data and radiocarbon dating, Wu et al. verify that the flood occurred and place the start of the Xia dynasty at about 1900 BC, thus reconciling the historical and archaeological chronologies (see the Perspective by Montgomery). Science , this issue p. 579 ; see also p. 538

Isochron burial dating with cosmogenic nuclides is used in Quaternary geochronology for dating sediments in caves, terraces, basins, and other depositional environments. However, the method has seldom been rigorously tested against an independent chronology. Here, we report a direct comparison of isochron burial dating with K-Ar and 40Ar/39Ar bracketing ages on volcanic flows that sandwich a fluvial gravel layer in the Xinjiang province of northwestern China. The ages agree to within analytical uncertainty, validating the assumptions and physical constants used in the isochron burial dating method.

Interbasin groundwater flow (IGF) can play a significant role in the generation and geochemical evolution of streamflow. However, it is exceedingly difficult to identify IGF and to determine the location and quantity of water that is exchanged between watersheds. How does IGF affect landscape/watershed geomorphic evolution? Can geomorphic metrics be used to identify the presence of IGF? We examine these questions in two adjacent sedimentary watersheds in northern New Mexico using a combination of geomorphic/landscape metrics, springflow residence times, and spatial geochemical patterns. IGF is expressed geomorphically in the landscape placement of springs and flow direction and shape of stream channels. Springs emerge preferentially on one side of stream valleys where landscape incision has intercepted IGF flow paths. Stream channels grow toward the IGF source and show little bifurcation. In addition, radiocarbon residence times of springs decrease and the geochemical composition of springs changes as the connection to IGF is lost.

Canteen Kopje, situated in the Northern Cape Province of South Africa, has two main archaeological deposits: alluvial gravels and a mantle of overlying fine sediments known locally as the “Hutton Sands.” This paper focuses on the fine sediments, the three industries contained within them, and the interface with the underlying gravels in an attempt to clarify their formation and transformation. A Fauresmith assemblage is found at this interface; it is thus crucial to understand the processes of deposition and modification at this poorly understood boundary. The methods used in this study involved the analysis of artifact depositional (dip and orientation) and spatial data, artifact condition, raw materials, and assemblage size profiles. Data presented document the mixing between the lowest levels of the fine sediments and the underlying alluvial gravels. This study thus provides important contextual information for the Fauresmith industry at Canteen Kopje.

Sediments of the Plio-Pleistocene Guadix – Baza basin have provided a wealth of information on the first hominin populations in Western Europe. To better constrain the age of the Fuente Nueva-3 archaeological site within the basin, and to complement previous magnetostratigraphic studies, two vertical boreholes were taken that provide a continuous record of the lower part of the sequence. Results indicate that the sequence is dominated by negative inclinations, but some additional intervals with positive inclination are also identified in the lower part of the sequence. A new cosmogenic nuclide burial age of 1.50 ± 0.31 Ma helps constrain the magnetostratigraphic record. The abundance of normal polarity directions at the bottom of a borehole may indicate proximity to the Olduvai Subchron; however, further analyses are required to confirm this hypothesis.

With the discovery of Homo erectus teeth, stone artifacts and a rich fauna, Bailong Cave in northern Hubei Province is an important hominin/archaeological site in China. However, due to the lack of suitable dating methods, the previous age estimates all come from biostratigraphic correlations. Here we report the first application of a radio-isotopic dating method to the site. Three 26Al/10Be measurements of two quartz samples give a weighted mean burial age of 0.76 ± 0.06 million years (Ma, 1σ). Taking into account possible bias of the dating method, stratigraphic order and evidence for rapid sedimentation, the cultural deposits of the site should be somewhat younger than the above date. This is consistent with previous biostratigraphic age estimates at around the Early/Middle Pleistocene transition, and possibly indicates an earlier human coexistence with Stegodon–Ailuropoda fauna than previously estimated.

The Yuanmou H. erectus site is generally considered to be one of the oldest hominin sites in southern China. The chronology of this site has been repeatedly investigated using magnetostratigraphy since its first discovery in the 1960s. However, there are multiple interpretations of the magnetostratigraphy due to the complexity of the sedimentary environment, resulting in a one million year age discrepancy by different studies. Because Yuanmou's age has yet to be verified radio-isotopically, we apply isochron 26Al/10Be burial dating to constrain the existing magnetostratigraphy. Six samples from a gravel bed 38 m above the fossil layer were collected, yielding an age of 1.54 ± 0.06 (0.11) My. Based on the estimated sedimentation rate, we interpolate an age of 1.72 ± 0.03 My for the fossil layer. This result is consistent with the most recent paleomagnetic stratigraphy of 1.7 My for the Yuanmou H. erectus fossils. Combined with other recent chronological studies of paleoanthropological sites across Asia, this study supports a model for earlier hominin dispersals out of Africa.

The upper Colorado River basin drains the western slope of the Rocky Mountains province of North America and hosts a rich record of fluvial terraces and volcanic deposits that provide an archive of bedrock river incision since the Late Miocene. Here we present new geochronology from fluvial deposits and associated volcanic units using multiple methods (luminescence, cosmogenic-burial, 40Ar/39Ar basalt and detrital sanidine, and U/Pb detrital zircon) to reconstruct a detailed record of bedrock incision in the upper Colorado River over timescales ranging from Miocene to Late Pleistocene. Late Miocene (ca. 11–8 Ma) basalt flows perched 800–1700 m above the Colorado River, and the oldest known ancestral Colorado River deposits preserved beneath basalt flows on Grand Mesa, provide the basis for average, long-term (∼107 yr) incision rates. Rates range from ∼110–160 m/Ma between Grand Junction (downstream) and Glenwood Canyon (upstream), with rates decreasing upvalley. Intermediate-scale (∼105–106 yr) incision rates are ∼200–320 m/m.y. over the past 1–3 Ma, and these rates are faster than the average over the past 8–11 Ma. Short-term (

Geochronology and thermochronology combine geochemistry, nuclear reactions, and technology to probe the history and dynamics of Earth and planetary processes.

Meteoric 10Be concentrations in soil were measured to understand the mechanism, timescale, and climatic dependence of soil formation in the hyper-arid Atacama Desert. The observed systematic decline of soil 10Be concentrations with depth has been reproduced using a simple model that assumes soil matrix, including 10Be, builds up as layers over time while 10Be decays in situ. This suggests a mechanism of soil accumulation via atmospheric deposition, which is in agreement with stable isotopic evidence. The model estimates an age of ∼6.6 ± 0.4 Ma for the total soil profile. Small discrepancies between the model and observations are likely mainly due to changes in precipitation rates that can impact 10Be delivery rates and 10Be movement within the profile. Interpreted in this way, the 10Be data suggest drying in the Atacama after ∼4.7 Ma, and returning to an insignificant wet period at ∼1 Ma, which was possibly connected to El Nino- or La Nina-like climate change.

The cave infills at Sterkfontein contain one of the richest assemblages of Australopithecus fossils in the world, including the nearly complete skeleton StW 573 ('Little Foot') in its lower section, as well as early stone tools in higher sections. However, the chronology of the site remains controversial owing to the complex history of cave infilling. Much of the existing chronology based on uranium-lead dating and palaeomagnetic stratigraphy has recently been called into question by the recognition that dated flowstones fill cavities formed within previously cemented breccias and therefore do not form a stratigraphic sequence. Earlier dating with cosmogenic nuclides suffered a high degree of uncertainty and has been questioned on grounds of sediment reworking. Here we use isochron burial dating with cosmogenic aluminium-26 and beryllium-10 to show that the breccia containing StW 573 did not undergo significant reworking, and that it was deposited 3.67 ± 0.16 million years ago, far earlier than the 2.2 million year flowstones found within it. The skeleton is thus coeval with early Australopithecus afarensis in eastern Africa. We also date the earliest stone tools at Sterkfontein to 2.18 ± 0.21 million years ago, placing them in the Oldowan at a time similar to that found elsewhere in South Africa at Swartkans and Wonderwerk.

Water plays a critical role in erosion and sediment transport and this relationship is most evident in the hyperarid Atacama Desert of Northern Chile, a region characterized by erosion rates that fall to near zero and cobbles and boulders with cosmogenic nuclide concentrations indicative of exposure for many millions of years. Cosmogenic nuclide concentrations from the Atacama are used to both determine the age of hyperaridity onset and to place important constraints on rates of geomorphic processes in this uniquely arid environment. Prior determinations of cosmogenic nuclide concentrations from the Atacama Desert focus primarily on exposure ages from boulders/cobbles or erosion rates from bedrock. However, recent determinations of cosmogenic nuclide concentrations from boulders, bedrock, and sediment at the same location suggests that material from diverse sample types have different cosmogenic nuclide concentrations. Therefore, it is critical to determine which concentrations of cosmogenic nuclides are most representative of overall erosion rates from the Atacama. Here, concentrations of cosmogenic nuclides in more than 100 samples across two east-west transects within the central Atacama Desert (22-26°S) of Northern Chile are considered. Concentrations of 10Be and 26Al were measured in samples of bedrock, alluvial sediment, active stream sediment, and boulders within several sub-regions of the Atacama Desert, including: the western and eastern Coastal Cordillera, the inner absolute desert (including the Cerro de los Tetas), the Cordillera Domeyko, and the western flank of the Andes. This data allows detailed comparisons of cosmogenic nuclides concentrations both within diverse sample types at a given site and between major geomorphic sub-regions of the Atacama. The general pattern of cosmogenic nuclide concentrations in hyperarid environments is characterized by concentrations that are higher in boulders, moderately high in bedrock, lower in hillslope sediment, and lowest in channels that flow across the desert. At many locations in the central Atacama, boulders and bedrock have erosion rates as much as an order of magnitude slower than that of finer grained sediment at the same location, a relationship that is attributed to the fact that boulders sit above thick gypcrete soils. The hillslope to basin concentrations of cosmogenic nuclides within each sub-region, along with 26Al/10Be ratios, suggests that concentrations of 10Be in most bedrock and sediments reflects erosion rates. However, in the western Coastal Cordillera 10Be concentrations in sediment also reflects transport time. The overarching trend in this data set is that inferred erosion rates are lower to both the east and the west, corresponding with increases in both precipitation and erosion rates towards both the Andean Flank and in the Coastal Cordillera. This trend is previously noted for the Atacama; however, this large data set allows the first observation of the influence of other variables upon erosion rates. Most notably, another clear influence on erosion rates in the Atacama is slope. In some cases, differences in slope are enough to overcome the influence of aridity. For example, erosion rates on the flanks of the Cordillera Domeyko are faster (>1 m/Ma) than that at the crest (