Yongxin Pan

New evidence on the earliest human presence at high northern latitudes in northeast Asia

The timing of early human dispersal to Asia is a central issue in the study of human evolution. Excavations in predominantly lacustrine sediments at Majuangou, Nihewan basin, north China, uncovered four layers of indisputable hominin stone tools. Here we report magnetostratigraphic results that constrain the age of the four artefact layers to an interval of nearly 340,000 yr between the Olduvai subchron and the Cobb Mountain event. The lowest layer, about 1.66 million years old (Myr), provides the oldest record of stone-tool processing of animal tissues in east Asia. The highest layer, at about 1.32 Myr, correlates with the stone tool layer at Xiaochangliang, previously considered the oldest archaeological site in this region. The findings at Majuangou indicate that the oldest known human presence in northeast Asia at 40° N is only slightly younger than that in western Asia. This result implies that a long yet rapid migration from Africa, possibly initiated during a phase of warm climate, enabled early human populations to inhabit northern latitudes of east Asia over a prolonged period.

Magnetoferritin nanoparticles for targeting and visualizing tumour tissues

Engineered nanoparticles have been used to provide diagnostic, therapeutic and prognostic information about the status of disease. Nanoparticles developed for these purposes are typically modified with targeting ligands (such as antibodies, peptides or small molecules) or contrast agents using complicated processes and expensive reagents. Moreover, this approach can lead to an excess of ligands on the nanoparticle surface, and this causes non-specific binding and aggregation of nanoparticles, which decreases detection sensitivity. Here, we show that magnetoferritin nanoparticles (M-HFn) can be used to target and visualize tumour tissues without the use of any targeting ligands or contrast agents. Iron oxide nanoparticles are encapsulated inside a recombinant human heavy-chain ferritin (HFn) protein shell, which binds to tumour cells that overexpress transferrin receptor 1 (TfR1). The iron oxide core catalyses the oxidation of peroxidase substrates in the presence of hydrogen peroxide to produce a colour reaction that is used to visualize tumour tissues. We examined 474 clinical specimens from patients with nine types of cancer and verified that these nanoparticles can distinguish cancerous cells from normal cells with a sensitivity of 98% and specificity of 95%.

Earliest presence of humans in northeast Asia

The timing of the earliest habitation and oldest stone technologies in different regions of the world remains a contentious topic in the study of human evolution. Here we contribute to this debate with detailed magnetostratigraphic results on two exposed parallel sections of lacustrine sediments at Xiaochangliang in the Nihewan Basin, north China; these results place stringent controls on the age of Palaeolithic stone artifacts that were originally reported over two decades ago. Our palaeomagnetic findings indicate that the artifact layer resides in a reverse polarity magnetozone bounded by the Olduvai and Jaramillo subchrons. Coupled with an estimated rate of sedimentation, these findings constrain the layers age to roughly 1.36 million years ago. This result represents the age of the oldest known stone assemblage comprising recognizable types of Palaeolithic tool in east Asia, and the earliest definite occupation in this region as far north as 40° N.

Magnetic proxy climate results from the Duanjiapo loess section, southernmost extremity of the Chinese loess plateau

We report mineral magnetic results from a 7.5 m loess sequence (150 samples) from the southernmost extremity of the Chinese loess plateau (which includes the last two glacial cycles). In this area the loess sediments experienced particularly intense weathering processes. The magnetic assemblage is dominated by a mixture of pseudo-single domain (PSD) and multidomain (MD) magnetite with associated superparamagnetic (SP) grains of either magnetite or maghemite in the paleosols and weathered loess horizons. All the rock magnetic parameters fluctuate in parallel with marine sediment δ18O data over the last 150 kyr, thus reflecting changing global paleoclimatic conditions. This relationship is also supported by the evidence of Milankovitch cycles in the magnetic susceptibility record. Paleorainfall estimates, when compared with other studies from the Chinese loess plateau, underline the (more) humid character of this region during the last ∼130 kyr.

Mechanism of the magnetic susceptibility enhancements of the Chinese loess

Chinese loess/paleosol sequences have been regarded as excellent continental archives for encoding continuous paleoclimatic variations over the past 2.5 Myr. However, the mechanism for magnetic enhancements (especially the low-field mass-specific magnetic susceptibility, χ) of Chinese paleosols is still not completely resolved. This study quantifies contributions of aeolian and pedogenic magnetic particles to the bulk magnetic properties of the Chinese loess/paleosols by using a magnetic extraction technique. Magnetic properties of magnetic separates (extractable) and the corresponding residues (nonextractable) for five characteristic samples covering both loesses and paleosols were comprehensively investigated by hysteresis loops, frequency and low-temperature dependence of magnetic susceptibility, and interparametric ratios. Results show that (1) with moderate degrees of pedogenesis (χ (10–12) × 10−7 m3 kg−1, contributions of pedogenically related fine-grained pseudosingle-domain (PSD, ∼100 nm to several microns) particles become significant; (2) pedogenic particles have a narrow grain size distribution concentrated above the SP/SD threshold; and (3) anhysteretic remanent magnetization (ARM) is carried dominantly by SD grains. Moreover, we propose that only the nonextractable fraction of χ, saturation magnetization (M s) and remanent magnetization (M rs) show a strong relationship with the degree of pedogenesis. This new interpretation of magnetic enhancements helps us to retrieve more accurate and quantitative paleoclimatic signals recorded by the Chinese loess/paleosol sequences.

Rock magnetic properties related to thermal treatment of siderite: Behavior and interpretation

Detailed analyses of rock magnetic experiments were conducted on the oxidation products of high-purity natural crystalline siderite that were thermally treated in air atmosphere. Susceptibilities increase sharply between 400° and 530°C indicative of some new ferrimagnetic mineral phase generation. Both a drop (between 540° and 590°C) on the heating cycle and a dramatic increase (from 590°C to 520°C) on the cooling cycle occurred and are well consistent with the characteristic of magnetite. A distinct Hopkinson-type susceptibility peak indicates that hematite is the terminal product if siderite is heated to 700°C over and over. It has been revealed in detail that the original inverse magnetic susceptibility fabric contributed by the crystalline anisotropy of siderite in siderite-bearing specimens is changed to a normal magnetic fabric during incremental heating over 410°–490°C. This is a result of dominant contributions from the distribution anisotropy of newly transformed ferromagnetic minerals. A strong chemical-viscous remanent magnetization could be produced during siderite oxidation in an external field. Rock magnetic experimental results show that magnetite, maghemite, and hematite are the transformation products of high-temperature oxidation of siderite in air. Maghemite was not completely inverted to hematite even at temperature as high as 690°C during incremental thermal treatments. The mineral transformation processes were confirmed by conventional optical microscopic observation, X-ray diffractometry and Mossbauer spectroscopic analyses. These results indicate that the rock magnetic methods used here are reliable and highly sensitive in detecting very small magnetic phase changes in rocks. We conclude that these temperaturedependent variations of magnetic properties can be used as criteria for identification of siderite in rocks and sediments. Furthermore, it is clear that great care should be exercised in thermal demagnetization of siderite-bearing rocks in paleomagnetic, magnetic anisotropy, and rock magnetic studies.

Early evidence of the genus Homo in East Asia

The timing and route of the earliest dispersal from Africa to Eastern Asia are contentious topics in the study of early human evolution because Asian hominin fossil sites with precise age constraints are very limited. Here we report new high-resolution magnetostratigraphic results that place stringent age controls on excavated hominin incisors and stone tools from the Yuanmou Basin, southwest China. The hominin-bearing layer resides in a reverse polarity magnetozone just above the upper boundary of the Olduvai subchron, yielding an estimated age of 1.7Ma. The finding represents the age of the earliest documented presence of Homo, with affinities to Homo erectus, in mainland East Asia. This age estimate is roughly the same as for H. erectus in island Southeast Asia and immediately prior to the oldest archaeological evidence in northeast Asia. Mammalian fauna and pollen obtained directly from the hominin site indicate that the Yuanmou hominins lived in a varied habitat of open vegetation with patches of bushland and forest on an alluvial fan close to a lake or swamp. The age and location are consistent with a rapid southern migration route of initial hominin populations into Eastern Asia.

Toward Cloning of the Magnetotactic Metagenome: Identification of Magnetosome Island Gene Clusters in Uncultivated Magnetotactic Bacteria from Different Aquatic Sediments

ABSTRACT In this report, we describe the selective cloning of large DNA fragments from magnetotactic metagenomes from various aquatic habitats. This was achieved by a two-step magnetic enrichment which allowed the mass collection of environmental magnetotactic bacteria (MTB) virtually free of nonmagnetic contaminants. Four fosmid libraries were constructed and screened by end sequencing and hybridization analysis using heterologous magnetosome gene probes. A total of 14 fosmids were fully sequenced. We identified and characterized two fosmids, most likely originating from two different alphaproteobacterial strains of MTB that contain several putative operons with homology to the magnetosome island (MAI) of cultivated MTB. This is the first evidence that uncultivated MTB exhibit similar yet differing organizations of the MAI, which may account for the diversity in biomineralization and magnetotaxis observed in MTB from various environments.

Grain sizes of susceptibility and anhysteretic remanent magnetization carriers in Chinese loess/paleosol sequences

Detailed rock magnetic studies show that susceptibility (mass-specific χ) and anhysteretic remanent magnetization (ARM) of the Chinese loess/paleosol sequences are carried by almost identical magnetic carriers. Therefore the ratio Δχ/χARM (or equivalently χARM/Δχ, where Δχ is defined as χ − χ0, and χ0 is the intercept susceptibility of the plot of χ versus ARM, and χARM is field-normalized ARM) can be used to quantify the grain size of χ and ARM carriers. By determining this ratio for three Chinese loess/paleosol profiles (Jiuzhoutai, Yuanbao, and Yichuan) characterized by different degrees of environmentally controlled pedogenesis and sedimentation rates, we show that the lower grain-size limit of aeolian magnetic particles in the less pedogenically altered loess units is about 100–300 nm, in the finer-grained pseudosingle domain (PSD) grain-size range. In contrast, the grain sizes of pedogenically produced magnetic particles for mature paleosols dominantly cover both the superparamagnetic (SP) and single-domain (SD) ranges. On the basis of plots of Δχ/χARM against Δχ, samples can be divided into four regions (I, II, III, and IV). Region I corresponds to the least pedogenically altered primary loess samples, with Δχ/χARM of 0.165–0.24. Samples in region II, a transition zone between the least altered loess and the onset of development of paleosols, have χ values identical to those in region I but have lower Δχ/χARM of 0.09–0.165. With increasing susceptibility in zone III, Δχ/χARM is positively correlated with Δχ, indicating the gradually increasing influence of SP particles. Finally, in zone IV with Δχ higher than ∼6.5 × 10−7 m3 kg−1, Δχ/χARM is independent of the variations in Δχ, suggesting that Δχ/χARM is totally controlled by the pedogenic finest-grained particles and the size distribution of these particles remains almost constant. The development of soils in the Chinese loess revealed by these three profiles from three sites can be clearly explained by a continuous process of pedogenesis, increasing from zone I to zone IV. The definition of the pedogenic zones can help to improve our understanding of the underlying mechanisms and variability of pedogenesis and thus could enable more successful and accurate separation of the authentic pedogenic signals from the background signal of the aeolian inputs at different loess sites worldwide.

Geomagnetic excursions recorded in Chinese loess in the last 70,000 years

Detailed paleomagnetic investigations conducted on the Malan loess (L1) at a well-dated section (Weinan) in the Chinese Loess Plateau revealed two distinct anomalous directional intervals (ADI) accompanied by lower relative paleointensity. Rock magnetic properties and anisotropy of magnetic susceptibility (AMS) of samples taken from sedimentary horizons carrying the anomalous directions are similar to those taken from outside the anomalous directional intervals. Thus, the anomalous directions are interpreted as geomagnetic excursions. Based on 14C and TL data, the excursions occurred at 27.1–26.0 and 46.8–37.4 kyr B.P; the ages are consistent with the ages assigned to the Mono Lake excursion (MLE) and Laschamp excursion (LE), respectively. The result indicates that the MLE and LE were independent geomagnetic excursions. The morphology of LE at this section suggests that the LE might be an aborted geomagnetic reversal.