Humans gorged on giant mole rats during Ethiopian glaciation

Read at Earth-logs about how Middle Stone Age humans survived 40 thousand years ago in a high-elevation glacial environment in Ethiopia by roasting giant mole rats.

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Startled giant mole rat caught at the surface in the Bale Mountains of Ethiopia

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Dear Earth-pages readers,

It is almost two decades since I was invited to write a regular series of articles on developments in the geosciences at Earth-pages. The site’s archives comprise more than 1200 of my commentaries, covering over 1500 publications. Since 2011 its annual readership has been between 40,000 to 80,000. Sadly, Earth-pages closed on August 1 2019 and no new posts will be added to it. Instead, activity has been transferred to a new site called Earth-logs. Titles of new additions to Earth-logs will continue to be posted here with, links to the full text.

Given its wide and loyal readership, I believe that the Earth-pages archives will continue to remain useful, especially for students, teachers and those hoping to begin geoscientific research. So, with the permission of Wiley-Blackwell, they too have been transferred to the new Earth-logs site .

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The format is different: the early posts (2000 to 2018) are logged annually under 12 broad themes: GeohazardsGeomorphologyHuman evolution and migrationsMagmatismMiscellaneous CommentaryPalaeoclimatologyPalaeobioloy; Physical ResourcesPlanetary ScienceRemote SensingSedimentology and Stratigraphy, and Tectonics. Each of these pages indexes the research topics covered during each year, along with links to PDFs of the annual logs.

New posts are added regularly to the Earth-logs Home Page. I intend to continue writing these commentaries in the same style as I have adopted at Earth-pages, for as long as I can. An important addition is direct web access to most of the papers on which the posts and the entries in annual logs are based, so that readers can download them as PDFs for their own use.

Thanks for reading my stuff here. Hopefully you will continue to do so at Earth-logs

Steve Drury

Metamorphic evidence of plate tectonic evolution

Read about tracking ancient paired metamorphic belts using data mining and statistics as a guide to the evolution of modern plate tectonics at Earth-logs

Almenning, Norway. The red-brown mineral is ga...

Eclogite: the red-brown mineral is garnet, omphacite is green and there is some white quartz.(credit: Kevin Walsh via Wikipedia)

Ediacaran glaciated surface in China

Read about a unique confirmation of Snowball Earth conditions during the Ediacaran Period at Earth-logs.

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29 Ma old striated pavement beneath the Carboniferous Dwyka Tillite in South Africa (credit: M.J Hambrey)

Ecological hazards of ocean-floor mining

Read about the threat posed by deep-ocean mining of polymetallic nodules at Earth-logs

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The distribution of potential ocean-floor metal-rich resources (Credit: Hefferman 2019)

 

A dinosaur nesting colony

Read about a new discovery in Mongolia at Earth-logs

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Clutch of near-spherical dinosaur eggs from Mongolia: scale bar = 10 cm. (Credit: Kanaka et al. 2019; Fig. 2A)

Out of Africa: The earliest modern human to leave

The 2017 discovery in Morocco of fossilised, anatomically modern humans (AMH) dated at 286 ka (see: Origin of anatomically modern humans, June 2017) pushed back the origin of our species by at least 100 ka. Indeed, the same site yielded flint tools around 315 ka old. Aside from indicating our antiquity, the Jebel Irhoud discovery expanded the time span during which AMH might have wandered into Eurasia, as a whole variety of earlier hominins had managed since about 1.8 Ma ago. Sure enough, the widely accepted earliest modern human migrants from Skhul and Qafzeh caves in Israel (90 to 120 ka) were superseded in 2018 by AMH fossils at Misliya Cave, also in Israel, in association with 177 ka stone artefacts (see Earliest departure of modern humans from Africa, January 2018). Such early dates helped make more sense of very old ages for unaccompanied stone tools in the Arabian Peninsula as tracers for early migration routes. Unlike today, Arabia was a fertile place during a series of monsoon-related cycles extending back to about 160 ka (see: Arabia : staging post for human migrations? September 2014; Wet spells in Arabia and human migration, March 2015). The ‘record’ has now shifted to Greece.

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Key ages of early H. sapiens, Neanderthals and Denisovans (credit: Delson, 2019; Fig. 1)

Fossil human remains unearthed decades ago often undergo revised assessment as more precise dating methods and anatomical ideas become available. Such is the case for two partial human skulls found in the Apidima Cave complex of southern Greece during the late 1970s. Now, using the uranium-series method, one has been dated at 170 ka, the other being at least 210 ka old (Harvati, K. and 11 others 2019. Apidima Cave fossils provide earliest evidence of Homo sapiens in Eurasia. Nature, v. 571 online; DOI: 10.1038/s41586-019-1376-z). These are well within the age range of European Neanderthals. Indeed, the younger one does have the characteristic Neanderthal brow ridges and elongated shape. Albeit damaged, the older skull is more rounded and lacks the Neanderthals’ ‘bun’-like bulge at the back; it is an early member of Homo sapiens. In fact 170 ka older than any other early European AMH, and a clear contemporary of the long-lived Neanderthal population of Eurasia; in fact the age relations could indicate that Neanderthals replaced these early AMH migrants.

Given suitable climatic conditions in the Levant and Arabia, those areas are the closest to Africa to which they are linked by an ‘easy’, overland route. To reach Greece is not only a longer haul from the Red Sea isthmus but involves the significant barrier of the Dardanelles strait, or it requires navigation across the Mediterranean Sea. Such is the ‘specky’ occurrence of hominin fossils in both space and time that a new geographic outlier such as Apidima doesn’t help much in understanding how migration happened. Until – and if – DNA can be extracted it is impossible to tell if AMH-Neanderthal hybridisation occurred at such an early date and if the 210 ka population in Greece vanished without a trace or left a sign in the genomics of living humans. Yet, both time and place being so unexpected, the discovery raises optimism of further discoveries to come

Ancient proteins: keys to early human evolution?

A jawbone discovered in a Tibetan cave turned out to be that of a Denisovan who had lived and died there about 160,000 years ago (see: Denisovan on top of the world; 6 May, 2019). That discovery owed nothing to ancient DNA, because the fossil proved to contain none that could be sequenced. But the dentine in one of two molar teeth embedded in the partial jaw did yield protein. The teeth are extremely large and have three roots, rather than the four more common in modern, non-Asian humans, as are Denisovan teeth from in the Siberian Denisova Cave. Fortunately, those teeth also yielded proteins. In an analogous way to the genomic sequencing of nucleotides (adenine, thymine, guanine and cytosine) in DNA, the sequence of amino acids from which proteins are built can also be analysed. Such a proteomic sequence can be compared with others in a similar manner to genetic sequences in DNA. The Tibetan and Siberian dentine proteins are statistically almost the same.

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Triple helix structure of collagen, colour-coded to represent different amino acids (credit: Wikipedia)

At present the most ancient human DNA that has been recovered – from an early Neanderthal in the Sima de los Huesos in Spain – is 430,000 years old (see: Mitochondrial DNA from 400 thousand year old humans; December 2013). Yet it is proving difficult to go beyond that time, even in the cool climates that slow down the degradation of DNA. The oldest known genome of any animal is that of mtDNA from a 560–780 thousand year old horse, a leg bone of which was extracted from permafrost in the Yukon Territory, Canada. The technologies on which sequencing of ancient DNA depends may advance, but, until then, tracing the human evolutionary journey back beyond Neanderthals and Denisovans seems dependent on proteomic approaches (Warren, M. 2019. Move over, DNA: ancient proteins are starting to reveal humanity’s history. Nature, v. 570, p. 433-436; DOI: 10.1038/d41586-019-01986-x). Are the earlier Homo heidelbergensis and H. erectuswithin reach?

It seems that they may be, as might even earlier hominins. The 1.8 Ma Dmanisi site in Georgia, now famous for fossils of the earliest humans known to have left Africa, also yielded an extinct rhinoceros (Stephanorhinus). Proteins have been extracted from it, which show that Stephanorhinus was closely related to the later woolly rhinoceros (Coelodonta antiquitatis). Collagen protein sequences from a 3.4 Ma camel preserved in the Arctic and even from a Tanzanian 3.8 Ma ostrich egg shell show the huge potential of ancient proteomics. Most exciting is that last example, not only because it extends the potential age range to that of Australopithecus afarensis but into tropical regions where DNA is at its most fragile. Matthew Warren points out potential difficulties, such as the limit of a few thousand amino acids in protein sequences compared with 3 million variants in DNA, and the fact that the most commonly found fossil proteins – collagens –  may have evolved very little. On the positive side, proteins have been detected in a 195 Ma old fossil dinosaur. But some earlier reports of intact diosaur proteins have been questioned recently (Saitta, E.T. et al. 2019. Cretaceous dinosaur bone contains recent organic material and provides an environment conducive to microbial communities. eLife,8:e46205; DOI: 10.7554/eLife.46205)

Multiple invention of stone tools

Steadily, the record of stone tools has progressed further back in time as archaeological surveys have expanded, especially in East Africa (Stone tools go even further back, May 2015). The earliest known tools – now termed Lomekwian – are 3.3 million years old, from deposits in north-western Kenya, as are cut-marked bone fragments from Ethiopia’s Afar region. There is no direct link to their makers, but at least six species ofAustralopithecus occupied Africa during the Middle Pliocene. Similarly, there are various options for who made Oldowan tools in the period between 2.6 and 2.0 Ma, the only known direct association being with Homo habilis in 2.0 Ma old sediments from Tanzania’s Olduvai Gorge; the type locality for the Oldowan.

The shapes of stone tools and the manufacturing techniques required to make them and other artefacts, are among the best, if not the only, means of assessing the cognitive abilities of their makers. A new, detailed study of the shapes of 327 Oldowan tools from a 2.6 Ma old site in Afar, Ethiopia has revealed a major shift in hominin working methods (Braun, D.R. and 17 others 2019. Earliest known Oldowan artifacts at >2.58 Ma from Ledi-Geraru, Ethiopia, highlight early technological diversity. Proceedings of the National Academy, v. 116, p. 11712-11717; DOI: 10.1073/pnas.1820177116). The sharp-edged tools were made by more complex methods than the Lomekwian. Analysis suggests that they were probably made by striking two lumps of rock together, i.e. by a deliberate two-handed technique. On the other hand, Lomekwian tools derived simply by repeatedly bashing one rock against a hard surface, not much different from the way some living primates make rudimentary tools. But the morphology of the Ledi-Geraru tools also falls into several distinct types, each suggesting systematic removal of only 2 or 3 flakes to make a sharp edge. The variations in technique suggest that several different groups with different traditions used the once lake-side site.

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Various 2.6 Ma old Oldowan stone tools from Ledi-Geraru, Ethiopia (credit: Braun et al., 2019)

Ledi-Geraru lies about 5 km from another site dated about 200 ka earlier than the tools, which yielded a hominin jawbone, likely to be from the earliest known member of the genus Homo. A key feature that suggested a human affinity is the nature of the teeth that differ markedly from those of contemporary and earlier australopithecines. It appears that the tools are of early human manufacture. The ecosystem suggested by bones of other animals, such as antelope and giraffe was probably open grassland – a more difficult environment for hominin subsistence. The time of the Lomekwian tools was one of significantly denser vegetation, with more opportunities for gathering plant foods. Perhaps this environmental shift was instrumental in driving hominins to increased scavenging of meat, the selection pressure acting on culture to demand tools sharp enough to remove meat from the prey of other animals quickly, and on physiology and cognitive power to achieve that.

See also: Solly, M. 2019. Humans may have been crafting stone tools for 2.6 million years (Smithsonian Magazine)

Geochemical background to the Ediacaran explosion

The first clear and abundant signs of multicelled organisms appear in the geological record during the 635 to 541 Ma Ediacaran Period of the Neoproterozoic, named from the Ediacara Hills of South Australia where they were first discovered in the late 19thcentury. But it wasn’t until 1956, when schoolchildren fossicking in Charnwood Forest north of Leicester in Britain found similar body impressions in rocks that were clearly Precambrian age that it was realised the organism predated the Cambrian Explosion of life. Subsequently they have turned-up on all continents that preserve rocks of that age (see: Larging the Ediacaran, March 2011). The oldest of them, in the form of small discs, date back to about 610 Ma, while suspected embryos of multicelled eukaryotes are as old as the very start of the Edicaran (see; Precambrian bonanza for palaeoembryologists, August 2006).

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Artist’s impression of the Ediacaran Fauna (credit: Science)

The Ediacaran fauna appeared soon after the Marinoan Snowball Earth glaciogenic sediments that lies at the top of the preceding Cryogenian Period (650-635 Ma), which began with far longer Sturtian glaciation (715-680 Ma). A lesser climatic event – the 580 Ma old Gaskiers glaciation – just preceded the full blooming of the Ediacaran fauna. Geologists have to go back 400 million years to find an earlier glacial epoch at the outset of the Palaeoproterozoic. Each of those Snowball Earth events was broadly associated with increased availability of molecular oxygen in seawater and the atmosphere. Of course, eukaryote life depends on oxygen. So, is there a connection between prolonged, severe climatic events and leaps in the history of life? It does look that way, but begs the question of how Snowball Earth events were themselves triggered.

There are now large amounts of geochemical data from Neoproterozoic sedimentary rocks that bear on processes in the atmosphere, seawater, continental crust and the biosphere of the time. Some are indicative of the reducing/oxidising (redox) potentials of ocean water in which various sediments were deposited. Carbon isotopes chart organic burial and the abundance of CO2 in the oceans and atmosphere. Strontium isotopes give details of the rates of continental erosion. The age statistics of zircon grains in sediments are useful; the proportion of zircons close in age to the time of sediment deposition relative to older grains is a proxy for the rate of continental-arc volcanism and thus for subduction rates. Joshua Williams of Britain’s University of Exeter and colleagues from the universities of Edinburgh and Leeds have used complex modelling to assess the pace at which oxygen was added to the surface environment through the Ediacaran Period (Williams, J.J. et al. 2019. A tectonically driven Ediacaran oxygenation eventNature Communications, v.  10 (1); DOI: 10.1038/s41467-019-10286-x).

They estimate a 50% increase in atmospheric oxygen during the Ediacaran to about 0.25 % of the present concentration, which would be sufficient to support large, mobile animals. They attribute this primarily to a boost in the supply of CO2 to the atmosphere as a result of increased volcanic activity. This would have warmed the surface environment so that exposed rock on the continents underwent accelerated chemical weathering. By freeing from continental crust increased amounts of nutrients, such as phosphorus and potassium, the boost to photosynthesis would have increased the oceanic biomass, thereby emitting oxygen. Multicelled animals would have been beneficiaries of such a transformation. The trend continued into the Cambrian, thereby unleashing the explosion of animals and their evolution that continued through the Phanerozoic. Ultimately, the trigger was increased Late-Neoproterozoic tectonic activity that drove the massive Pan-African orogeny and the accretion of the Gondwana supercontinent.

See also: https://www.sciencedaily.com/releases/2019/06/190619130315.htm

Note added, 26 June 2019: Roger Mason has referred me to the carbon-isotope record during the Ediacaran. It shows some of the stratigraphic record’s largest negative δ13C excursions in carbonate rocks (Tahata, M. and 10 others 2013. Carbon and oxygen isotope chemostratigraphies of the Yangtze platform, South China: Decoding temperature and environmental changes through the EdiacaranGondwana Research, v.23, p. 333-353; DOI: 10.1016/j.gr.2012.04.005). Such isotopic excursions went on throughout the Ediacaran, along with sudden fossil appearances and disappearances – so-called ‘Strangelove’ oceans – plus fluctuations in sediment types and climate. The Ediacaran was a wild time in most respects.

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Geochemical changes recorded in the complete Ediacaran sedimentary sequence of the Three Gorges of the Yangtze River, China (credit: Tahata et al. 2013; Fig. 4)