4.1 Observation results of skull morphology
As shown in Fig. 2, the skull and facial bone of RG1 were incomplete, only part of the left facial bone was seen, the skull bone was relatively intact, and the mandible was intact. The facial bone of RG2 on the right side of the skull is mutilated, the skull is relatively intact, and the mandible is intact.
Table 1
The main index of the skull
Items
|
RG1
|
RG2
|
Index
|
Type
|
Index
|
Type
|
Cranial index
|
75.5
|
Mid-cranial
|
70.4
|
Long skull
|
Cranial height index
|
74.1
|
Ortho-cranial
|
77.2
|
Tall skull
|
Cranial width and height index
|
98.1
|
Narrow skull
|
109.6
|
Narrow skull
|
Forehead width
|
66.3
|
Mid-forehead
|
69.8
|
Generous
|
Foramen magnum index
|
90.4
|
Generous
|
-
|
-
|
Upper index
|
-
|
-
|
-
|
-
|
Orbital IndexⅠ
|
Left
|
83.8
|
Mid-orbit
|
-
|
-
|
Right
|
-
|
-
|
82.6
|
Mid-orbit
|
Orbital IndexⅡ
|
Left
|
85.5
|
Mid-orbit
|
-
|
-
|
Right
|
-
|
-
|
89.9
|
High orbit
|
Nose index
|
47.4
|
Mid-nose
|
-
-
|
Palatal index
|
85.4
|
Broad palate
|
-
-
|
Facial protrusion index
|
-
|
-
|
93.8
Orthognathic
|
Table 2
Non-measured characteristics of the skull at Shenna ruins
Observation items
|
RG1
|
RG2
|
Cranial shape
|
Oval
|
Oval
|
Eyebrow protrusion
|
Medium
|
Weak
|
Eyebrow bow range
|
<1/2
|
<1/2
|
Forehead
|
Medium
|
Medium
|
Cranial suture
|
Bregma section
|
Deep wave
|
Zigzag wave
|
Top section
|
Deep wave
|
Zigzag wave
|
Top hole section
|
Microwave
|
Deep wave
|
Back section
|
Microwave
|
Zigzag wave
|
Mastoid
|
Small
|
Medium
|
Carina
|
Slightly obvious
|
Slightly obvious
|
Orbital
|
Square
|
-
|
Pear-shaped hole
|
Pear-shaped
|
Heart-shaped
|
Lower edge of pear-shaped hole
|
Anterior nasal fossa-shaped
|
Sharp
|
Nasal spines
|
Grade I
|
-
|
Canine fossa
|
Weak
|
Weak
|
Nasal depression
|
Shallow
|
Shallow
|
Wing area
|
Top butterfly-shaped
|
Top butterfly-shaped
|
Nasal bridge
|
-
|
Concave
|
Nasal bone
|
-
|
Type I
|
Top hole
|
No
|
All left and right
|
Sagittal crest
|
Weak
|
Medium
|
Forehead seam
|
No
|
No
|
Palatine
|
U type
|
V type
|
Palate pillow
|
Crest-shaped
|
-
|
Chin type
|
Pointed shape
|
Round shape
|
Mandibular angle
|
Eversion
|
Eversion
|
Mental hole position
|
P2 position
|
P2M1 position
|
Mandibular pillow
|
Small
|
-
|
Lower jaw of rocking chair
|
Obviously rocking chair
|
Slightly rocking chair
|
The skull measurement data and Non-measured characteristics of the skull at Shenna ruins (Tab. 1, Tab. 2) show that the skull shape is mainly oval and elliptical, the eyebrow arch is underdeveloped, the orbital shape can be square and rectangular, the nasal spines are not obvious, the canine fossa is weak, the nasal root is shallow, the pear-shaped hole is eccentric, the pear shape lower edge of the shaped hole is sharp. The remaining two lower jaws are rocking chair type. The skull is long, moderately high, and obviously in narrow skull. The forehead width is mainly wide-headed and medium-forehead. The orbit is mainly of middle orbit type and low orbit type. The nose shape is moderate in width, mostly middle nose shape. The phylogenetic type should belong to the Mongolian race and have certain characteristics of East Asian race.
As shown in Fig. 3, the most of the measurement data and corresponding indicators fall within the Mongolian race variation range, but the skull width is smaller than the common variation range, and the skull width and height index is too large, and the RG1 and RG2 width and height index is greater than the variation range. The overall judgment should belong to the Mongolian race and have certain characteristics of East Asian race. The craniofacial characteristics of the residents of the Shenna site are consistent with the life characteristics of the time they lived in.
4.2 The pH values of the burial environment
Table 3
The pH value of the burial environment at ruins
Sampling location
|
pH
|
Average value
|
RG2
|
8.16
|
8.10
|
8.14
|
8.13
|
Around RG2
|
7.87
|
7.91
|
7.87
|
7.88
|
Southwest RG2
|
8.15
|
8.14
|
8.14
|
8.14
|
Table 3 shows that the pH value of the remains and the burial environment at ruins ranges from 7.8 to 8.2, indicating that the bones at the Shenna ruins are stored in an alkaline environment for a long time and are not easy to preserve organic components, which has aggravated the corrosion of the remains. The studies have shown that pH value of the burial environment at the Shenna ruins is mostly neutral or alkaline, mainly result of that most of the soil contains Ca2+, which is consistent with the location of the Shenna ruins in the northwest of our country and its unique soil properties.
4.3 Microstructure and composition
By using modern pig bones instead of modern human bones as a comparison sample, the comparison of the microscopic morphologies of the remains and modern pig bones was observed by the Scanning Electronic Microscopy. The Fig. 2-a show the cross-sectional microscopic morphology of the remains [16], there are pores of different sizes. Compared with the pig bone where the pores of Fig. 4-b are filled with organic matter such as bone marrow and grease, only trabecular bone remains in the remains to maintain the structure. Due to the interaction of inorganic bone minerals and organic matrix in natural bones, natural bones have good mechanical properties such as pressure resistance and flexural resistance, while the organic components are almost invisible in the picture a, which is also one of the reasons for the decrease of the mechanical strength of the remains. Fig. 4-c shows the microscopic morphology of part of the pores are filled with some other materials, which is preliminarily guessed as under the migration of water and other effects the pores in the cancellous bone with a large adsorption area were filled with soil. Fig. 4-e shows that the trabecular bone is full of tiny pores, the inorganic matter in the remains is the destruction and organic matter are decomposed, and the bones are covered with holes of different sizes, unlike the dense and compact structure of pig bone in Fig. 4-f, which becomes loose and porous and are suitable filling pipes for groundwater and soil, etc., so as to further erode the bones, accelerate the process of fragility of the remains, and directly cause the phenomenon of crunching and powdering of the remains.
The energy dispersive spectrometry (EDS) analysis is performed on the soil samples and remains of buried human remains, and the test results are shown in Fig. 5, revealing the types and percentages of elements contained in the soil samples. The top three elements with the most content are oxygen, calcium and silicon elements with mass fractions of 39.6%, 30.37% and 15.44%. It can be preliminarily inferred from the element types and contents that the main components of the soil at the Shenna ruins may contain quartz (SiO2) and calcium carbonate (CaCO3). As Fig. 5 shows that the main content of calcium, oxygen, silicon and phosphorus in human bones, which occupy 34.71%, 34.06%, 11.83% and 7.31% respectively, in addition, the calculated relative molar ratio of Ca/P can be as high as 3.67, which is inconsistent with the uncontaminated bone-like Ca/P ratio studied in the literature. The content of calcium is much higher and is speculated that the much higher content of calcium is assumed to be mostly due to the high content of calcium carbonate in the soil of Shenna ruins.
The remains are mainly composed of biogenic hydroxyapatite. Hydroxyapatite in fresh bone is generally in a weak crystalline state. After burial, some amorphous hydroxyapatite will change into a crystalline structure through diagenesis, resulting in increased crystallinity. The structure and composition of apatite will change during burial and diagenesis. XRD analysis can provide a basis for determining whether the bones are contaminated and whether they can be used for further element analysis, as shown in Fig. 6-c, it shows the XRD spectrum peaks of the soil. From the corresponding PDF card information, it shows that the soil is mainly composed of quartz SiO2 and limestone CaCO3, which is consistent with the estimation of element composition and content data in EDS analysis, also explains the reason for the alkaline soil pH. The content of CaCO3 in soil existence also provides strong data to prove the conjecture that the Ca element in the EDS test results on the surface of the remains is too high. Retrieving the remains before and after ashing through PDF card data, and as shown in Fig. 6-a, the characteristic peaks of calcium hydroxyphosphate (Ca10(PO4)6(OH)2), while that of pig bones before and after ashing is (Ca10(PO4)5CO3(OH)) the characteristic peak, and it is due to the frequent occurrence of CO32− to PO43− ion substitution phenomenon in organisms. The crystal structure of hydroxyapatite will not be destroyed by this substitution, and it is not in the scope of chemical pollution, so it belongs to normal substitution.
In the comparison of the X-ray Diffractiometry (XRD) of the remains and the pig bone samples before and after the ashing treatment, it shows that the half high width value of the XRD characteristic peaks is smaller than that of the unashed sample. The diffraction peaks of the sample after chemical treatment become stronger and sharper, indicating that ashing [17] will not only burn off organic components, but also improve the crystallinity of hydroxyapatite, which changes in the phase and microstructure of hydroxyapatite can cause changes in hydroxyapatite, and ashing can eliminate this effect caused by the phase. The diffraction peaks of pig bones are severely broadened before ashing, that is, the crystallinity is poor, but the diffraction peaks after ashing treatment have obvious changes. After the remains are ashed, the intensity and sharpness of the XRD diffraction peaks have also been significantly improved. It also proves that the remains samples in this paper are not contaminated and can still be used for meaningful scientific research. At the same time, the characteristic peaks of hydroxyapatite in the XRD spectrum show strong and sharp signals, it can be further concluded that although the burial for thousands of years has a certain stimulating effect on the decomposition of organic matter in the bone sample, but the influence on the composition of inorganic substances is relatively weak.
In the infrared spectrum [18–25], 3576 cm−1 is the absorption vibration peak of H2O, which appears in all, but the weaker in the B and D curves, may be due to the large amount of water evaporation caused by high temperature ashing, which is adsorbed to the air during the grinding process. The asymmetric stretching vibrations of C-H are at 853 cm−1, 2924 cm−1, while vibration peaks of -COOH and amide Ⅰ and Ⅱ appear at 1746 cm−1 and 1543 cm−1, 1662 cm−1, respectively, these indicate that there are oil, bone marrow, protein and other substances in the pig bone, but they do not appear after ashing, the high temperature burns out the organic components in the bone during the ashing process. In addtion, the relatively weak vibration peaks of amides I and II appeared in curve A, indicating that there are still some organic remaining in the remains in the thousands of years of burial. Near 1455 cm−1 is the vibration peak of CO32−, which appears in curves A and B, but the XRD spectra of the remains before and after ashing only detect the characteristics of (Ca10(PO4)6(OH)2), this may be because the characteristic peak of PO43− is too strong, which masks the vibration peak of CO32−. 873cm−1 is classified as the contribution of HPO42−, which is consistent with the small amount of CaHPO4·2H2O in fresh bone. All curves have strong and sharp characteristic peaks at 1037 cm−1, 564 cm−1 and 604 cm−1, which represent the existence of PO43−, indicating that even in the underground environment, the composition of the remains is decomposed in a large amount, the inorganic structure is destroyed, which will eventually cause looseness and porosity and decrease in mechanical properties, however, the composition of inorganic minerals has not been changed or contaminated.