Search

As a contribution towards a regional environmental context of human-climate interactions, the ICDP co-funded Chew Bahir Drilling Project, a part of the HSPDP (Hominin Sites and Paleolakes Drilling Project), recovered ~280-m long cores of sedimentary strata through continental scientific drilling in southern Ethiopia. The fluvio-lacustrine coring locality in the Chew Bahir basin is situated near key archaeological and paleoanthropological sites, such as the Omo-Kibish where the Omo 1 and 2 Homo sapiens fossils were recovered.Here we present the 620,000-year environmental record from Chew Bahir that provides an extraordinary opportunity to examine the potential influence of climate variability on hominin evolution, cultural innovation and dispersal during the Middle to Late Pleistocene. The near-continuous Chew Bahir record documents 13 environmental episodes that differ in length and character, potentially inducing habitat changes influencing hominin biological and cultural transformation. We infer that long-lasting and relatively stable humid conditions from ~620,000–275,000 years BP (Episodes 1–6) were interrupted by several abrupt and extreme hydroclimatic oscillations. This phase coincided with the appearance of high anatomical diversity in hominin groups. During Episodes 7–9 (~275,000–60,000 years BP), a pronounced pattern of climatic cyclicity was paralleled by the gradual transition from Acheulean to Middle Stone Age technologies, the emergence of H. sapiens in eastern Africa, and a key phase of human social and cultural innovation. Episodes 10–12 (~60,000–10,000 years BP), marked by high-frequency climate oscillations, is contemporaneous with the global dispersal of H. sapiens, facilitated by continued technological innovation and the alignment of humid pulses between eastern Africa and the eastern Mediterranean.Prospectively, the Chew Bahir record represents a crucial component for the Middle and Late Pleistocene in the ongoing efforts of the scientific community (future and upcoming ICDP-funded projects) to address questions in Africa across four topical core areas: paleoclimate, paleoenvironment, basin evolution, and modern lake systems.

The East African Rift System (EARS) is a key location for studying Plio-Pleistocene paleoclimate and hominin inhabitance. The region experienced profound reorganization during this interval as a response to volcanism, tectonics and climate change, and arguably detailed spatiotemporally coherent climate datasets could provide evidence of causal links between geologic change and hominin evolution. However, continued tectonism, erosion, burial and volcanism obscures much of this information. Despite its rich fossil record, the Turkana basin in the northern Kenya Rift is no exception. It has been hypothesized that Lake Turkana and paleo-Lake Suguta to its south formed one 530-650 km long mega-lake before 221 ka ago, and was a major barrier for E-W dispersal of hominids and other terrestrial fauna. Here we present new information on basin development based on paleolandscape modeling and 87Sr/86Sr analysis on microfossils of newly discovered paleo-lake sequences in the Suguta Valley, permitting reconstruction of volcano-tectonic processes 900-700 ka ago. Contrary to previous assumptions, results suggest that two to three lakes separated by tectono-volcanic barriers formed instead of one mega-lake. These results have implications for previously formulated hypotheses about mega-lakes preventing W-E migration and exchange and suggest that during the early Middle Pleistocene E-W migrations were possible.

The study of the mid-Holocene climate tipping point in tropical and subtropical Africa is the subject of current research, not only because there is a comparatively simple but nonlinear relationship between the change in cause (orbital forcing) and the accelerated response of the monsoon system, but also because the African monsoon is an example of a potentially positive evolution of living conditions for humans: modeling results suggest that the Sahel is expanding northward in the wake of human-induced recent global warming, with green belts spreading northward. New literature distinguishes tipping elements such as the African monsoon according to the nature of the cause and the response of the climate system. Research here focuses primarily on tipping points of the type, which is characterized by a critical slowing down and a decreasing recovery from perturbations. The African monsoon, on the other hand, is an example of the tipping point of the type, which is characterized by flickering before the transition. The two types also differ in the nature of their early warning signals (EWS). These EWS are increasingly becoming the focus of research, as they are particularly important for predicting possible tipping of climate in the future of our planet. For the African monsoon system, flickering between two stable states near the transition has been predicted by modeling, but has not yet been demonstrated on paleoclimate time series.The paleoenvironmental record from the Chew Bahir Basin in the southern Ethiopian Rift, which documents the climate history of eastern Africa of the past ~620 ka with decadal resolution in some parts provides the possibility to examine the termination of the African Humid Period (AHP, ~15–5 kyr BP) with regard to the possible occurrence of EWS. Thanks to six well-dated short sediment cores (

In this study, we synthesize terrestrial and marine proxy records, spanning the past 620,000 years, to decipher pan-African climate variability and its drivers and potential linkages to hominin evolution. We find a tight correlation between moisture availability across Africa to El Niño Southern Ocean oscillation (ENSO) variability, a manifestation of the Walker Circulation, that was most likely driven by changes in Earth’s eccentricity. Our results demonstrate that low-latitude insolation was a prominent driver of pan-African climate change during the Middle to Late Pleistocene. We argue that these low-latitude climate processes governed the dispersion and evolution of vegetation as well as mammals in eastern and western Africa by increasing resource-rich and stable ecotonal settings thought to have been important to early modern humans.

During the last 5 Ma the Earth's ocean-atmosphere system passed through several major transitions, many of which are discussed as possible triggers for human evolution. A classic in this context is the possible influence of the closure of the Panama Strait, the intensification of Northern Hemisphere Glaciation, a stepwise increase in aridity in Africa, and the first appearance of the genus Homo about 2.5 - 2.7 Ma ago. Apart from the fact that the correlation between these events does not necessarily imply causality, many attempts to establish a relationship between climate and evolution fail due to the challenge of precisely localizing an a priori unknown number of changes potentially underlying complex climate records. The kernel-based Bayesian inference approach applied here allows inferring the location, generic shape, and temporal scale of multiple transitions in established records of Plio-Pleistocene African climate. By defining a transparent probabilistic analysis strategy, we are able to identify conjoint changes occurring across the investigated terrigenous dust records from Ocean Drilling Programme (ODP) sites in the Atlantic Ocean (ODP 659), Arabian (ODP 721/722) and Mediterranean Sea (ODP 967). The study indicates a two-step transition in the African climate proxy records at (2.35-2.10) Ma and (1.70 - 1.50) Ma, that may be associated with the reorganization of the Hadley-Walker Circulation. .

Spectral analysis is a technique of time-series analysis that decomposes signals into linear combinations of harmonic components. Rooted in the 19th century, spectral analysis gained popularity in palaeoclimatology since the early 1980s. This was partly due to the availability of long time series of past climates, but also the development of new, partly adapted methods and the increasing spread of affordable personal computers. This paper reviews the most important methods of spectral analysis for palaeoclimate time series and discusses the prerequisites for their application as well as advantages and disadvantages. The paper also offers an overview of suitable software, as well as computer code for using the methods on synthetic examples.

The Chew Bahir Drilling Project (CBDP) aims to test possible linkages between climate and evolution in Africa through the analysis of sediment cores that have recorded environmental changes in the Chew Bahir basin. In this statistical project we consider the Chew Bahir palaeolake to be a dynamical system consisting of interactions between its different components, such as the waterbody, the sediment beneath lake, and the organisms living within and around the lake. Recurrence is a common feature of such dynamical systems, with recurring patterns in the state of the system reflecting typical influences. Identifying and defining these influences contributes significantly to our understanding of the dynamics of the system. Different recurring changes in precipitation, evaporation, and wind speed in the Chew Bahir basin could result in similar (but not identical) conditions in the lake (e.g., depth and area of the lake, alkalinity and salinity of the lake water, species assemblages in the water body, and diagenesis in the sediments). Recurrence plots (RPs) are graphic displays of such recurring states within a system. Measures of complexity were subsequently introduced to complement the visual inspection of recurrence plots, and provide quantitative descriptions for use in recurrence quantification analysis (RQA). We present and discuss herein results from an RQA on the environmental record from six short (

Understanding eastern African paleoclimate is critical for contextualizing early human evolution, adaptation, and dispersal, yet Pleistocene climate of this region and its governing mechanisms remain poorly understood due to the lack of long, orbitally-resolved, terrestrial paleoclimate records. Here we present leaf wax hydrogen isotope records of rainfall from paleolake sediment cores from key time windows that resolve long-term trends, variations, and high-latitude effects on tropical African precipitation. Eastern African rainfall was dominantly controlled by variations in low-latitude summer insolation during most of the early and middle Pleistocene, with little evidence that glacial–interglacial cycles impacted rainfall until the late Pleistocene. We observe the influence of high-latitude-driven climate processes emerging from the last interglacial (Marine Isotope Stage 5) to the present, an interval when glacial–interglacial cycles were strong and insolation forcing was weak. Our results demonstrate a variable response of eastern African rainfall to low-latitude insolation forcing and high-latitude-driven climate change, likely related to the relative strengths of these forcings through time and a threshold in monsoon sensitivity. We observe little difference in mean rainfall between the early, middle, and late Pleistocene, which suggests that orbitally-driven climate variations likely played a more significant role than gradual change in the relationship between early humans and their environment.

Reconstructions of climatic and environmental conditions can contribute to current debates about the factors that influenced early human dispersal within and beyond Africa. Here we analyse a 200,000-year multi-proxy paleoclimate record from Chew Bahir, a tectonic lake basin in the southern Ethiopian rift. Our record reveals two modes of climate change, both associated temporally and regionally with a specific type of human behavior. The first is a long-term trend towards greater aridity between 200,000 and 60,000 years ago, modulated by precession-driven wet-dry cycles. Here, more favorable wetter environmental conditions may have facilitated long-range human expansion into new territory, while less favorable dry periods may have led to spatial constriction and isolation of local human populations. The second mode of climate change observed since 60,000 years ago mimics millennial to centennial-scale Dansgaard-Oeschger cycles and Heinrich events. We hypothesize that human populations may have responded to these shorter climate fluctuations with local dispersal between montane and lowland habitats.

In this study, we synthesize terrestrial and marine proxy records, spanning the past 620 ky, to decipher pan-African climate variability and its drivers and potential linkages to hominin evolution. We find a tight correlation between moisture availability across Africa to El Niño Southern Ocean oscillation (ENSO) variability, a manifestation of the Walker Circulation, that was most likely driven by changes in Earth's eccentricity. Our results demonstrate that low-latitude insolation was a prominent driver of pan-African climate change during the Middle to Late Pleistocene. We argue that these low-latitude climate processes governed the dispersion and evolution of vegetation as well as mammals in eastern and western Africa by increasing resource-rich and stable ecotonal settings thought to have been important to early modern humans.

In this study we synthesize terrestrial and marine proxy records spanning the last 620,000 years, to decipher pan-African climate variability, its drivers and potential linkages to hominin evolution. We find a tight correlation between moisture availability across Africa to Walker and Hadley Circulation variability that were most likely driven by changes in Earth´s eccentricity. Our results demonstrate that low latitude insolation rather than glacial-interglacial cyclicity was the predominant driver of pan-African climate change during the mid to late Pleistocene. We argue that these low-latitude climate processes governed the dispersion and evolution of vegetation, as well as mammals, in eastern and western Africa, ultimately by increasing resource-rich and stable ecotonal settings that have long thought to have been the preferred habitats of hominins.

The hypothesis of a connection between the onset (or intensification) of Northern Hemisphere Glaciation (NHG), the stepwise increase in African aridity (and climate variability) and an important mammalian (including hominin) species turnover is a textbook example of the initiation of a scientific idea and its propagation in science. It is, however, also an example of the persistent popularity of a hypothesis despite mounting evidence against it. The first part of our work analyzes of the history of the scientific idea by seeking its roots, including coincidental meetings and exchanges between of scientists, at project meetings, conferences and workshops. The consequences of this idea are examined and its influence on subsequent scientific investigations both before and after it has been falsified. In the second part of our investigation, we examine why the idea that the high latitudes have a major control on the climate of the low latitudes and thus early human evolution persists. For this purpose, an attempt is made to understand the original interpretation of the data, with special consideration of the composition of the scientific team and their scientific backgrounds and persuasions. Some of the key records in support of the hypothesis of a step-wise transition will be statistically re-analyzed by fitting change-point models to the time series to determine the midpoint and duration of the transition – in case such a transition is found in the data. A critical review of key publications in support of such a connection and a statistical re-analysis of key data sets leads to three conclusions: (1) Northern Hemisphere Glaciation is a gradual process between ~3.5–2.5 Ma, not an abrupt onset, either at ~2.5 Ma, nor at ~2.8 Ma, or any other time in the Late Cenozoic Era, (2) the trend towards greater aridity in Africa during this period was also gradual, not stepwise in the sense of a consistent transition of a duration of ≤0.2 Ma, and (3) accordingly, a step-wise change in environmental conditions cannot be used to explain an important mammalian (including hominin) species turnover.

The formation of the East African Rift System led to the emergence of large topographical contrasts in southern Ethiopia. This extreme topography is in turn responsible for an extreme gradient in the distribution of precipitation between the dry lowlands (~500 mm a-1) in the surrounding of Lake Turkana and the moist western Ethiopian Highlands (~2,000 mm a-1). As a consequence, the prevailing vegetation is fractionated into a complex mosaic that includes desert scrubland along the Lake Turkana shore, woodlands and wooded grasslands in the Omo-River lowlands and the paleo-lake Chew Bahir catchment, afro-montane forests of the Ethiopian Highlands, and afro-alpine heath in most elevated parts. During the past 25 ka, southern Ethiopia has been exposed to significant climate changes, from a dry and cold Last Glacial Maximum (LGM, 25-18 ka BP) to the African Humid Period (AHP, 15-5 ka BP), and back to present-day dry conditions. These shifts in temperature and precipitation may have affected the vegetation pattern and landscape in the area, but environmental data especially from LGM times are rare. This is because in times of a dry climate the paleo-lake Chew Bahir was dried up and hence the climate record in lake sediments was interrupted.In this study, we investigate the hydrological conditions during the LGM using a previously-developed lake balance model (LBM) for southern Ethiopia, which is now coupled with a new predictive vegetation model (PVM) to better understand the biosphere-hydrosphere interactions and thus possible precipitation thresholds. The PVM is based on the method of boosted regression trees using elevation and monthly precipitation as input to predict land-cover, tree-cover and vegetation greenness for a ~1 km grid covering the Omo-River, paleo-lake Chew Bahir, Lake Chamo and Lake Abaya catchments. We linked the PVM and the resulting land surface parameters with the LBM to model the impact of a changing land-cover to the actual evaporation. Furthermore, we used the glycerol dialkyl glycerol tetraethers (GDGT) based paleo-temperature and tropical lapse rate reconstructions from Mount Kenya to consider the orographic temperature distribution in southern Ethiopia during the LGM. Using both, we simulated different precipitation amounts from 100% to 50% compared to the modern-day multi-annual averages and their effect on vegetation and lake levels of paleo-lake Chew Bahir. Our biosphere-hydrosphere modelling approach suggests 25 to 30% lower moisture availability during the LGM compared to the modern conditions and provides a high-resolution spatial reconstruction of the potential prevailing vegetation in the southern Ethiopian region.

This chapter first summarizes the gravimetric and magnetic properties of the earth as well as the weather in relation to the state of the earth’s atmosphere (Sect. 8.2). It then describes the most common ways of acquiring and storing gravimetric, magnetic, and weather data (Sects. 8.3, 8.4). The subsequent exercises (Sect. 8.5) demonstrate how to measure mineral densities, determine gravitational acceleration using a pendulum, determine the position, velocity, and acceleration of an elevator, carry out a magnetic survey using a LEGO/smartphone setup, and acquire weather data, subsequently streaming it to the Internet of Things (IoT) platform ThingSpeak.

This chapter first summarizes the most important elastic properties of the earth, from the atmosphere to the hydrosphere and the deep interior of our planet, and introduces the most important types of elastic waves (Sect. 7.2). It then describes the main methods used to acquire and store elastic signals (Sects. 7.3–7.4). The subsequent exercises then demonstrate how to use a smartphone’s multi-purpose accelerometer as a seismometer, how to use smartphone and webcam microphones to measure the distance and direction to a sound source, and how to analyze sound in the time and frequency domains for harmonic signals and noise (Sect. 7.5).

This book introduces methods of geoscientific data acquisition using MATLAB in combination with inexpensive data acquisition hardware such as sensors in smartphones, sensors that come with the LEGO MINDSTORMS set, webcams with stereo microphones, and affordable spectral and thermal cameras. The text includes 35 exercises in data acquisition, such as using a smartphone to acquire stereo images of rock specimens from which to calculate point clouds, using visible and near-infrared spectral cameras to classify the minerals in rocks, using thermal cameras to differentiate between different types of surface such as between soil and vegetation, localizing a sound source using travel time differences between pairs of microphones to localize a sound source, quantifying the total harmonic distortion and signal-to-noise ratio of acoustic and elastic signals, acquiring and streaming meteorological data using application programming interfaces, wireless networks, and internet of things platforms, determining the spatial resolution of ultrasonic and optical sensors, and detecting magnetic anomalies using a smartphone magnetometer mounted on a LEGO MINDSTORMS scanner.

The geological record shows that abrupt changes in the Earth system can occur on timescales short enough to challenge the capacity of human societies to adapt to environmental pressures. In many cases, abrupt changes arise from slow changes in one component of the Earth system that eventually pass a critical threshold, or tipping point, after which impacts cascade through coupled climate–ecological–social systems. The chance of detecting abrupt changes and tipping points increases with the length of observations. The geological record provides the only long-term information we have on the conditions and processes that can drive physical, ecological and social systems into new states or organizational structures that may be irreversible within human time frames. Here, we use well-documented abrupt changes of the past 30 kyr to illustrate how their impacts cascade through the Earth system. We review useful indicators of upcoming abrupt changes, or early warning signals, and provide a perspective on the contributions of palaeoclimate science to the understanding of abrupt changes in the Earth system. A synthesis of intervals of rapid climatic change evident in the geological record reveals some of the Earth system processes and tipping points that could lead to similar events in the future.

This chapter is concerned with the acquisition, processing, and display of image data. We will first learn about the physical principles of electromagnetic waves, which include visible light (Sect. 5.2), and then discuss how cameras capture visible light images (Sect. 5.3). The various ways that raster data can be stored on a computer are explained in Sect. 5.4 and the main tools for importing, manipulating, and exporting image data are then presented in Sects. 5.5 and 5.6. We will then make use of the knowledge that we have gained to acquire, process, and display images to complete the exercises in Sect. 5.7.