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[QUOTE]Originally posted by DD'eDeN: [QB] So. Af. Caves redated <http://dx.doi.org/10.1038/s41586-018-0711-0> UPb-dated flowstones restrict South African early hominin record to dry climate phases. Robyn Pickering, Andy Herries, Jon Woodhead, John Hellstrom, Helen Green, Bence Paul, Terrence Ritzman, David Strait, Benjamin Schoville & Phillip Hancox 2018 Nature <https://www.nature.com/articles/s41586-018-0711-0.ris> The Cradle of Humankind preserves a rich collection of fossil hominins representing Australopithecus, Paranthropus & Homo. The ages of these fossils are contentious, and have compromised the degree to which the S.African hominin record can be used to test hypotheses of human evolution. But UPb analyses of horizontally bedded layers of CaCO3 (flow-stone) provide a potential opportunity to obtain a robust chronology. Flowstones are ubiquitous cave features, and provide a palaeo-climatic context: they grow only during phases of increased effective precipitation, ideally in closed caves. Here we show: flowstones from 8 Cradle caves date to 6 narrow time-intervals between 3.2 & 1.3 Ma. We use a kernel density estimate to combine 29 UPb ages into a single record of flowstone growth intervals. We interpret these as major wet phases: an increased water supply, more extensive vegetation cover & at least partially closed caves allowed for undisturbed semi-continuous growth of the flowstones. The intervening times represent substantially drier phases, during which fossils of hominins & other fossils accumulated in open caves. Fossil preservation, restricted to drier intervals, thus biases the view of hominin evolutionary history & behaviour, it places the hominins in a community of comparatively dry-adapted fauna. Although the periods of cave closure leave temporal gaps in the S.African fossil record, the flowstones themselves provide valuable insights into local & pan-African climate variability. ______ South Africa's hominin record is a fair-weather friend 21.11.18 New research from Robyn Pickering cs is the first to provide a timeline for fossils from the caves within the Cradle of Humankind. It also sheds light on the climate conditions of our earliest ancestors in the area. It corrects assumptions that the region's fossil-rich caves could never be related to each other. In fact, the research suggests fossils from Cradle caves date to just 6 specific time-periods. Robyn Pickering: "Unlike previous dating work (which often focused on 1 cave, sometimes even just 1 chamber of the cave), we are providing - direct ages for 8 caves & - a model to explain the age of all the fossils from the entire region. Now we can link together the findings from separate caves, and create a better picture of evolutionary history in S-Africa." The Cradle is a World Heritage Site, made up of complex fossil-bearing caves. It's the world's richest early hominin site, home to nearly 40 % of all known human ancestor fossils (e.g. Au.africanus "Mrs Ples"). Using U-Pb dating, researchers analysed 28 flow-stone layers, found sandwiched between fossil-rich sediment in 8 caves across the Cradle: the fossils in these caves date to 6 narrow time-windows between 3.2 & 1.3 Ma: "The flowstones are the key. We know they can only grow in caves during wet times, when there is more rain outside the cave. By dating the flowstones, we are picking out these times of increased rainfall. We therefore know that during the times in between, when the caves were open, the climate was drier, more like what we currently experience." This means the early hominins living in the Cradle experienced big changes in local climate, from wetter to drier conditions, at least 6 times between 3 & 1 Ma, but only the drier times are preserved in the caves, skewing the record of early human evolution. Up until now, the lack of dating methods for Cradle fossils made it difficult to understand the relationship between E & S.African hominin spp. The S.African record has often been considered undateable, compared to E.Africa, where volcanic ash layers allow for high resolution dating. Andy Herries, co-author: "the S.African record was the first to show Africa as the origin point for humans, but the complexity of the caves & difficultly dating them has meant that the S.African record has remained difficult to interpret. In this study, we show that the flow-stones in the caves can act almost like the volcanic layers of E.Africa, forming in different caves at the same time, allowing us to directly relate their sequences & fossils into a regional sequence." Pickering began dating the Cradle caves in 2005, as part of her PhD research. This new publication is the result of 13 years of work. The results return the Cradle to the forefront, and open new opportunities to answer complex questions about human history in the region. Bernard Wood, no co-author: "Robyn cs have made a major contribution to our understanding of human evolution. This is the most important advance to be made since the fossils were discovered. Dates of fossils matter a lot. The value of the S-African evidence has been increased many-fold by this exemplary study of its temporal and depositional context." https://archaeologynewsnetwork.blogspot.com/2018/11/south-africas-hominin-r ecord-is-fair.html#jP5tdY208yUv22yV.99 [/QB][/QUOTE]
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