Improving the chronology of early human evolution

东非裂谷的图尔卡纳和阿瓦什盆地，保存了一份特殊的化石和考古记录，在很大程度上，构成了我们目前对早期人类环境的理解的基础。古代火山活动留下了大量的火山灰沉积物（凝灰岩），可以使用40Ar/39Ar的放射性测年方法来确定年代。虽然这种方法得到的日期很精确，但它只能提供具有明显时间间隔的大致范围，因为火山活动是断断续续的，凝灰岩并不总是在整个景观中存在。此外，尽管该地区有大量的考古发现和动物化石，但可确定年代的凝灰岩在东非大裂谷非常罕见。因此，年龄估计往往依赖于不精确的相对方法，如磁地层学和生物地层学。迫切需要一种获得绝对日期的方法，以便将东部裂谷内以及整个非洲的所有沉积序列联系起来，并帮助阐明上新世-更新世期间早期人类生物和文化事件的更广泛图景。同样，南非的网站也存在约会问题，尽管问题不同。在大多数情况下，它们都是岩溶充填体，直到最近才应用了基于宇宙成因和铀/铅同位素系统的绝对方法。这些技术也留下了巨大的空白和/或不能精确地确定化石或考古事件的年代。例如，U/Pb测年通常反映的是上垫或下垫流岩的年龄，而不是化石的年龄。我们建议应用一种新的基于发光的方法，即红外辐射荧光（IR-RF），该方法是该提案的指定研究员共同研究员帮助开发的，以确定肯尼亚，埃塞俄比亚和南非的化石和人工制品沉积物和/或火山凝灰岩的年龄（即沉积时间），并填补辐射技术遗漏的时间空白。红外-射频法广泛适用于测定年代所需的砂粒长石矿物颗粒，而且该技术的目标是富钾长石，这是地球上最常见的矿物之一。最近的研究表明，这种方法有可能将发光的年龄范围从50万年延长到400万年，从而涵盖了人类家族进化的大部分时间范围。在过去的五年中，记录和分析发光数据的方法有了显著的发展，包括改进的光检测和更先进的分析和统计技术，所有这些都导致了新的方法和更灵活的处理和可视化数据的方式。最近的技术进步，包括基于电子倍增电荷耦合器件（EMCCD）的单光子成像系统的发展，也表明现在是时候把这些新的尖端创新结合在一起，应用于早期人类进化的更可靠的年表。这项研究将极大地增加在保存早期人类进化关键证据的地区的年代确定的序列的数量，并使我们能够在将整个非洲的人类化石记录相关联方面提供重大改进。一个新的、更精细的时间框架将极大地提高我们对上新世以来早期人族所面临的适应挑战多样性的理解，它将有助于阐明气候和生态变化在推动人族进化中的作用这一激烈争论的问题。

The Turkana and Awash basins in the East African Rift, preserve an exceptional fossil and archaeological record and to a large extent, form the basis for our current understanding of early hominin environments. Ancient volcanic activity has left numerous ash deposits (tuffs) that can be dated using the radiometric dating method 40Ar/39Ar. Although precise, dates obtained by this method only provide broad envelopes with significant temporal gaps because volcanism is episodic, and tuffs do not always survive across the landscape. Furthermore, despite the abundance of archaeological finds and animal fossils in this region, datable tuffs are rare in the East African Rift. Consequently, age estimation often relies on imprecise relative methods, such as magnetostratigraphy and biostratigraphy. A method for obtaining absolute dates is urgently required in order to correlate all the sedimentary sequences within the eastern rift, as well as across Africa, and to help clarify the wider picture of early human biological and cultural events during the Plio-Pleistocene. Likewise, the South African sites also suffer from dating problems, albeit from different issues. In most of these cases they are karstic infills and only recently, have any absolute methods based on cosmogenic and uranium/lead isotope systems been applied. These techniques also leave huge gaps and/or do not precisely date the fossil or archaeological event of interest. For instance, U/Pb dates generally reflect the ages of over- or underlying flowstone and not that of a fossil.We propose to apply a novel luminescence-based method known as infrared-radiofluorescence (IR-RF), which the named researcher co-investigator on this proposal helped to develop, in order to determine the age (i.e. time of deposition) of fossil- and artefact-bearing sediments and/or volcanic tuffs in Kenya, Ethiopia and South Africa and to fill in the time gaps omitted by radiometric techniques. The IR-RF method is widely applicable due to the ubiquitous occurrence of sand sized feldspar mineral grains required for dating and the technique targets potassium- (K-) rich feldspar, one of the most common types of mineral on earth. Recent studies suggest that this methodology has the potential to extend the age range of luminescence dating from 0.5 million years to 4 million years, thus encompassing the majority of the time range over which the human family evolved. Methods of recording and analyzing luminescence data have developed significantly over the last five years, including improved light detection and more advanced analytical and statistical techniques, all of which have led to new approaches and more flexible ways of processing and visualizing data. Recent technological advances including the development of single photon imaging systems based on electron multiplying charge coupled devices (EMCCD) also suggest that the time is right to bring together and apply some of these new cutting-edge innovations to help achieve more reliable chronologies for early hominin evolution. This research will dramatically increase the number of well-dated sequences in areas archiving key evidence for early human evolution and it will enable us to provide significant improvements in correlating human fossil records across Africa. A new and more refined chronological framework will greatly improve our understanding of the diversity of adaptive challenges faced by early hominins since the Pliocene and it will help to shed more light on the hotly debated question of the role of climatic and ecological changes in driving hominin evolution.