First, the burial characteristics of biological fossils and ancient human sites
Many mammalian fossil sites and Paleolithic sites have been found in Nihewan Basin, and their burial characteristics provide rich physical data for studying the living environment of early ancient humans. However, the study of burial science in China is relatively weak, and only a few scholars make some simple discussions on burial science when studying fossils and paleolithic tools, lacking in-depth research. Therefore, it can only be roughly described here.
(A) the burial characteristics of paleontology
Paleontological fossils in Nihewan Basin have the following characteristics:
(1) So far, no complete animal bones have been found, and even complete skulls and limb bones are rare. In most cases, the broken bones of animals of different species are buried together, and the living environment of these animals is very different.
(2) Mammalian fossils are mostly buried in the gravel layer near the lake or the sand layer in the river bed.
(3) Except for fish and plant fossils, few mammalian fossils were found in the thin clay in the center of the lake.
(4) Mollusca fossils are mostly buried in black silt of swamp facies or flood plain facies.
The above burial characteristics show that the mammalian fossils in Nihewan Basin can be divided into in-situ burial and off-site burial. The opposite example is the Salawusu River fauna, where fossils have many complete bones. Sometimes five or six hairy rhinoceros fossils of different ages can be found in an excavation pit, and carnivorous fossils also have complete skeletons. It shows that these animals can't extricate themselves from the mud when drinking water by the lake, and they can see that adults and young individuals are buried together. Carnivores find trapped animals to hunt, and as a result, they get stuck in the mire and are devastated. The skeleton of the same animal was also found in Maquangou, Nihewan Basin, but it was not a complete skeleton. Elephant fossils were found here, buried in the clay layer by the lake. Many elephant footprints were found in the excavation pit, and the stratum was disturbed by elephant legs on the profile. There are other mammals related to elephant fossils, most of which are broken limb bones, and Paleolithic tools can be found near the fossils. These burial phenomena show that although it is lakeside clay deposit, elephants can walk on it and leave footprints, so no complete elephant fossil skeleton trapped in mud has been found. There is no tragedy that human beings are mired in this activity. Therefore, it can be speculated that this is a place for animals to drink water and a good place for humans to hunt. The captured animals were dismembered on the spot and even divided into meals. Perhaps once in a while, ancient humans could capture small or young large animals. Therefore, it is speculated that this is the site of ancient human activities, and paleontological fossils can be buried in situ.
Other mammalian fossil sites are also completely scattered bones of various animals, which are animal remains brought into the lake by rivers or slope water. They are further transported after rotting and scattering, and are irregularly scattered to a large area, so it is difficult to find complete individuals. The animal fossils found in ancient human sites are broken and scattered, and traces of artificial chopping can be found, indicating that these fossils are animal remains that have been transported and eaten by human beings. Therefore, it can be said that such mammalian fossil sites are buried in different places.
Most of the mollusk fossils are intact mussels, which have not been scoured. The sedimentary facies of buried strata are consistent with the living conditions of corresponding mollusks, and belong to in-situ burial.
(2) Buried features of ancient human sites
Many Paleolithic sites have been found in Nihewan Basin, which have the following characteristics:
(1) Early Paleolithic sites were found in the lakeside area, and some of them were buried by lacustrine gray-green loam, reflecting the process of lakes.
(2) Late Paleolithic sites were found in the terrace sedimentary facies. At that time, the lake had disappeared, and ancient people lived by the river, and the hydrological environment was basically the same as it is now.
(3) Some stone fragments and cores of Paleolithic sites can be spliced together, indicating that they were buried in situ.
(4) Paleolithic sites have associated mammalian fossils, which are broken and have traces of knocking or cutting.
(5) There are bedrock outcrops or river gravels near the site, which provided ancient humans with raw materials for making paleolithic tools.
The above burial characteristics show that most Paleolithic sites are buried in situ, which can reflect the living environment of ancient humans at that time.
Paleolithic sites are all located on the lakeside or river terrace, because they are close to the water source, which is not only convenient for the ancients to get water, but also a place for all kinds of animals to drink or eat, which is convenient for the ancients to hunt. Donggutuo Site, Cenjiawan Site and Xu Jiayao Site were obviously buried by lake sediments later, but some of the paleolithic tools in the sites can be assembled, and some have found a lot of stone balls, indicating that they have not been transported basically. Therefore, it is speculated that when ancient humans lived here, there was still a certain distance from the lake. It was dry here, and then the lake rose, so ancient humans had to move away, leaving paleolithic and animal bones buried by lake sediments. However, because the lake is shallow and the carrying capacity of lakeside waves is limited, paleolithic tools are basically still there, with only a few traces of wear and tear.
The trace analysis of paleolithic found in Xiaochangliang site shows that ancient humans mainly used them to process meat, indicating that ancient humans may have adopted a "corpse-eating" lifestyle at that time. In addition, it is also found that some paleolithic surfaces have parallel scratches and some have fracture surfaces. It shows that after the lake rose, it was affected by waves for a short time, and some scratches or broken surfaces appeared. But it was quickly buried by lake sediments, which should belong to the type of in-situ burial.
Stripes of ashes can be observed in the excavation section of Xu Jiayao site, and there is no obvious directional arrangement of bone fossils. The mixed accumulation of stone balls, stone chips and fossils shows that when the lake rises, they are quickly buried without disturbance, so there is no directional arrangement and sorting, and they also have the characteristics of in-situ burial.
A large number of paleolithic tools have been found in Cenjiawan site, and stone chips and cores can be spliced together, indicating that this is the place where ancient humans lived and made stone tools. When the lake flooded the site, these paleolithic tools were not transported away, which is also a feature of in-situ burial.
According to the above analysis, the distribution law of paleontological fossil sites and paleolithic sites in Nihewan Basin can be summarized as follows:
(1) is distributed in lakeside or river terrace deposits.
(2) The area near bedrock outcrop or river gravel layer.
(3) Paleontological fossil sites and paleolithic sites are mostly found in areas where lacustrine platforms or residual hills are eroded by gullies or cliffs.
Further searching for paleontological fossils or ancient human sites should pay full attention to the above distribution characteristics.
Second, the analysis of ancient human living environment
Nihewan rift basin, as a special geomorphic unit formed by plate tectonic movement, has been in an open basin geomorphic pattern surrounded by mountains on both sides for a long time since Neogene. The ecological environment of the basin is controlled by tectonic movement and global climate change. The Pliocene-Middle Pleistocene tectonic movement was active, and lakes existed in the basin for a long time. During this period, the environment of Nihewan rift basin responded to the global climate and environmental change process with its unique geomorphic conditions. The global climate change process since Pliocene has been deeply studied. Taking the sedimentary facies of sea ice raft and loess plateau in northern China as examples, the history of global climate change since Pliocene is summarized.
The study of global climate and environmental change shows that the earth's climate has gradually cooled since the early Eocene. The main reasons are the change of ocean current channel caused by plate movement, the uplift of Qinghai-Tibet Plateau and the decrease of atmospheric CO2. The cooling of the earth makes the ice sheet develop at the poles, so the change of ice raft debris content in the ocean core should be an indicator of the earth's climate. The gamma logging curve of ODP hole 883 near the Arctic Pacific Ocean of Ocean Drilling Program (ODP) shows that ice raft debris suddenly increased from 2.75Ma ago (de Monocal P, 1993), indicating that the global climate suddenly became cold (Figure 5-5).
Figure 5-5 Gamma-ray logging curve of ODP883 hole near the Arctic Pacific Ocean shows that ice raft debris deposition increased significantly 2.6 million years ago (according to de Menocal, 1993).
In ODP, the δ 18O records of deep-sea drilling cores were deeply studied, and the δ 18O results of Shackletonetal for ODP677 were obtained. The most representative (Shackleton et al., 1990). The δ 18O record of ODP677 * * has divided 106 deep-sea oxygen isotope stages. The aeolian sedimentary profile (loess-paleosol series) on the Loess Plateau in China has preserved complete Quaternary environmental information. According to the grain size analysis results of five loess-paleosol sequence profiles on the Loess Plateau, Ding Zhongli et al. established the "China loess grain size time cycle" and compared it with the deep-sea δ 18O record (Figure 5-6). Chiloparts has four peaks, namely L2, which is equivalent to MIS6, and its age is 0.128 ~ 0.19ma; L9 is equivalent to MIS22-24, and its age is 0.865 ~ 0.943MaL 15, which is 1.24 ~ 1.263 ma compared with MIS38. Compared with MIS10/-103, L33 is 2.547~2.59Ma. However, this special climate stage is not clearly reflected in the deep-sea oxygen isotope curve, which may be caused by regional extreme climate events (Ding et al., 2002).
Comparison between MIS stage and Chiloparts climate curve (according to Gradstein et al., 2004; Ding et al., 2002)
Under the background of global climate change, North China will certainly respond. The loess layer is the main part at the bottom of Xifeng loess profile in the loess plateau, with a thickness of 2. 5 mA from point B to 1. 909 ma b.p., and the accumulation time of loess layer is 0. The formation time of paleosol layer is 0. 17 mA, twice as much as the former. In other words, from 2. 5 milliamps, blood pressure to 2. 0 Ma b.p, the climate is mainly dry and cold, which should be a reflection of the expansion of the Arctic ice sheet on the Loess Plateau. From 2. 0 ma blood pressure to 0. The time period of loess-paleosol sequence shows that the time period of loess accumulation is 0. The time period of paleosol formation is 0. 742 Ma, which is 1.5 times of the former. It shows that the dry and cold period in this period is much less than the warm period, and the climate and environment are much warmer than 2, which is more suitable. 5 ~ 2.0 Ma B.P (Ding et al., 1994).
According to the ocean drilling plan and the loess research results in China, 2. 6 Mab.p is an important period of climate change. On May 2 1 2009, the International Stratigraphic Committee voted that the Quaternary is a period in the new geological chronostratigraphic table, and its lower limit is 2. The voting result of 6 Mab.p appropriately reflects the above research results (Yang Xiaoping, 2009). Nihewan fault basin since 2. 6 mabpp up to now. According to the research results of mammalian fossils and magnetostratigraphy of these profiles, combined with the records of MIS and Chiloparts, they are divided into five stages: Early Pleistocene (2. Middle and late Early Pleistocene (2. 0 ~ 0.8 Mab p), Middle Pleistocene (0. 8 ~ 0. 128 Mab p) and late Pleistocene (0. 128 ~ 0.0 1 monoclonal antibody). According to the ecological characteristics reflected by lithology, lithofacies, vertebrate and invertebrate fossils, the living environment of ancient humans at that time is discussed below.
① Early Pleistocene (2. 6 ~ 2.0 Mab.p .)
At present, according to the research of magnetic stratigraphy, Hongyanan 'gou section is the only section at the bottom of strata in the study area that reaches the M/G boundary (Zhu Rixiang et al., 2007). 1983, Zhou Kun Shu and others collected samples at the bottom of the profile at an altitude of 835 ~ 865 m. The results of sporopollen analysis showed that it recorded the evolution from coniferous forests such as fir, spruce and pine to grassland belts such as Artemisia and Chenopodium, and then to pine and spruce. It represents a relatively dry and cold climate, and its occurrence period is about 2. Six and two. 0 Ma B.P (see figure 3- 10). The expansion of the Arctic ice sheet in the early Early Pleistocene and the climatic characteristics of loess-paleosol sequence in the Loess Plateau are quite consistent with this (de MonocalP,1993; Ding et al., 1994). At present, the mammal fauna with exact dating results has not been found in Nihewan basin, which may reflect that the climate at that time was not suitable for the survival of most animals in Nihewan fauna. Tritoed horse And Chilean yeast. It was found in the Nangou section of Hongyan that it should be a Pliocene remnant species, representing a few remnant species that continued to that time during the great climate change period.
According to the research results of red weathering crust in China, Huang Zhenguo and others drew the distribution map of natural zones in the early early Pleistocene. Nihewan Basin is located at the junction of temperate zone and cold temperate zone, and Pliocene was warm temperate zone and north subtropical zone (Huang Zhenguo et al., 1996). The climate cooling at the beginning of early Pleistocene is consistent in the study of red weathering crust in China and the sporopollen analysis of Nihewan layer.
(2) Middle and late Early Pleistocene (2. 0 ~ 0.8 Mab.p .)
The latest research results of magnetic stratigraphy show that except for Hongya section in Nihewan layer, the bottoms of Huabaogou, Maquangou and Xiaochangliang sections are only exposed to Ordway events. Therefore, the strata below the B/M boundary of most sections of Nihewan layer belong to this period. Huabaogou Fauna, Dongyaozitou Fauna, Nihewan Fauna (in a narrow sense), Danangou Fauna, Ma Quan Gou Fauna, Xiaochangliang Fauna and Dongguto Fauna all lived in this period, and ancient human sites were mainly found in this period.
In the middle and late Early Pleistocene, the Nihewan Rift Basin was characterized by strong tectonic activity, volcanic eruption along the fault at the edge of the basin and rapid subsidence of the basin, which was the stage with the largest lake area. During this period, aeolian loess was widely accumulated on the Loess Plateau (Figure 5-7). Nihewan basin is located in the eastern margin of the Loess Plateau, and has also received some aeolian loess accumulation. Volcanic ash and loess settled in the lakeside area, which brought rich mineral nutrients to the soil. Vegetation around the lakeside and lake is lush, and all kinds of animals migrate here, which is the period with the highest biodiversity in Nihewan Basin. According to the analysis of the fossil composition of vertebrate fauna in this period, rodents, rabbits, odd-hoofed animals and cloven-hoofed animals are dominant, reflecting the environment of temperate arid grassland and forest grassland.
Figure 5-7 Paleoenvironment Restoration Map of Nihewan Basin in the Middle and Late Early Pleistocene
A detailed sporopollen analysis has been carried out on the section of Dadaopo in Nihewan Basin (Figure 3- 13) (Yin et al., 1996). According to the comparison of current research results of magnetostratigraphy, it is possible that the Ⅰ and Ⅱ zones delineated by sporopollen analysis of this profile should be roughly equal to 2 when the bottom only reaches Audoye's Iya polarity. The 0 ~ 0.8 Mab.p..I area is dominated by broad-leaved plants, including some typical subtropical plants, such as Liquidambar, Sapindaceae, Hymenoptera, Lygodium and so on. Tree pollen is mainly pine, oak, chestnut, Castanopsis fargesii, beech and so on. Gramineae pollen is very rich, mainly reflecting the subtropical climate environment, and the vegetation is mainly evergreen broad-leaved forest. The number and species of sporopollen in Area II are abundant, but the sporopollen representing subtropics has disappeared. Broad-leaved trees such as elm, birch and oak are common in temperate zones, while the pollen of pine, fir and spruce has increased. Artemisia and ephedra account for a considerable proportion, while Gramineae plants have decreased, showing a mild temperate climate. The above results of sporopollen analysis are consistent with 2. 0 to 0. The MIS curve and Chilop-arts curve were relatively stable in this period of 8mab.p., reflecting that the climate change was small. However, when the climate changed to the hot and humid direction, the area could still be in the subtropical environment. Therefore, some southern species such as shrew and rhinoceros Mei were found in some fauna. During this period, most members of the fauna lived in temperate zones, but the elephant and the rhinoceros Mei lived in tropics and subtropics. Their appearance in Nihewan area shows that in some periods, the climate conditions in Nihewan basin are good, close to the subtropical climate environment, or they can swim back here in summer.
According to the research results of weathering crust in China, the distribution map of natural zones in the middle and late Early Pleistocene shows that the subtropical northern boundary in North China can reach about 4 1 N (Huang Zhenguo et al., 1996). The vertebrate fossils in Nihewan Basin reflect the temperate grassland environment, and the conclusions of the two research fields are obviously different. The formation of red weathering crust needs a warm and humid environment. When the global climate changes to the hot and humid direction, red weathering crust can develop in the subtropical environment in North China. When the climate changes to dry and cold direction, North China is in an arid grassland environment, and the red weathering crust stops developing. However, the development of weathering crust is irreversible. When the climate becomes warm and humid again, it will continue to develop on the basis of the original red weathering crust. The preserved red weathering crust may be the product of repeated climate cycles, thus showing the characteristics of subtropical natural zones. Vertebrates can migrate repeatedly in the process of climate change, and their fossil records reflect the climatic environment in which these animals live. Therefore, the research conclusions of the two fields are not contradictory, but can complement and confirm each other.
In particular, both Nihewan Fauna (in a narrow sense) and Ma Quan Gully Fauna have found mammoth (Mammuthus trogontherii) in grassland, which is the place where this species first appeared. Therefore, it is speculated that the evolution from meridional mammoth to grassland mammoth was completed in Nihewan basin, and then they radiated around, and the evolution to true mammoth was completed in Siberia (Wei Cursor, 2008). The reason why the grassland mammoth can complete the species evolution here is that the Nihewan Basin has maintained a stable and suitable environment for a long geological period, so that the species have enough time to complete the process of species formation around it. By analogy, the early hominids living in Nihewan Basin in this period should also have suitable conditions and enough time to complete the evolution to Homo sapiens, which is a field that should be further studied in Nihewan Basin.
(3) Middle Pleistocene (0. 8 ~ 0. 128 Mab.p .)
The study of δ 18O records in the core of ODP806 station found the "Middle Pleistocene Revolution" event (MRP). Before 0.9MaB.P, the variation amplitude of the measured curve recorded by δ 18O is smaller than the theoretical calculation value, and then the variation amplitude of the two curves is basically the same. Since the quaternary δ 18O curve mainly reflects the size of the global ice sheet, it is judged that MRP leads to an increase of global ice volume of about 15% (Berger et al., 1993). This important event of global change has been clearly reflected in the Loess Plateau of China. During the period from 1.60 to 0.8mab.p., the climate change cycle is mainly 41ka; Up to now, the climate change cycle is dominated by10.8 ma b.p During this period, the loess accumulation time is 0. Paleosol formation time is 0. 34 Ma (Ding et al., 1994), indicating that the climate is obviously getting cold. Loess-paleosol sequence in the Loess Plateau is 0. 8 mabbp should be a reflection of the "Middle Pleistocene Revolution" in the Loess Plateau. The upper section of Nihewan layer in Nihewan basin is mainly yellow-green, so it is called "Huangnihewan layer". Underwater loess was found in Nihewan formation in this section in summer. These lithologic changes reflect that the climate is drier and colder than before.
Nihewan layer from 0. Eight to zero. 128 Ma, the species and genera of mammals are not as rich as those in the previous stage, mainly bighorn deer, hairy rhinoceros and horses in Sanggan River, reflecting the environment dominated by arid grassland. In the sporopollen analysis of Dadaopo section, Yuan divided the section into sporopollen zone III, and the number of Ulmus, Betula and Pinus was less than that of sporopollen zone II. The pollen of plants such as ephedra and Artemisia, which represent the arid and cold climate, increased sharply, while the pollen of Gramineae decreased obviously, and the pollen of Typha and Cyperaceae disappeared obviously, indicating that the climate is obviously developing in the direction of drought, and the sporopollen assemblage represents the semi-arid temperate climate environment (Yin et al., 1996). The research results of red weathering crust in Huang Zhenguo also show that the climate in this area is temperate, which is consistent with the above research results (Huang Zhenguo, 1996).
The period of early hominid activities in Nihewan Basin is basically the same as Nihewan fauna, and most of the animals in Nihewan fauna are probably the source of their food, which is also proved by mammalian fossils in ancient human sites. Therefore, it can be said that when ancient humans lived here, the climate was temperate, and in some periods, subtropical animals could swim back here in summer. Early ancient human sites were all located in the lakeside area. It is speculated that ancient humans lived on the lakeside at that time, so this is also a place where animal activities are concentrated. But so far, no trace of fire has been found, and it is still impossible to prove whether ancient humans knew about fire at that time. However, some sites have found sporadic fish bones, or they may have been able to fish.
Another important question is whether Nihewan Ancient Lake had an exit at that time. Is it a freshwater lake or a saltwater lake? According to the current research results of ostracods, in the early ancient human life, the ostracods in lake sediments were all freshwater ostracods. This means that the lake is fresh water. Occasionally foraminifera were found, but their species were single and their shells were deformed strongly, indicating that they were brought here by accident and survived in an unsuitable fresh water environment, which could not be used as evidence that the lake was salty.
If lakes in arid and semi-arid areas want to maintain fresh water environment for a long time, they must have outlets, so it can be inferred that Nihewan ancient lake had outlets at that time. Xia et al. studied the terraces of the canyon and found that the highest lacustrine terrace was consistent with the height of Heshangping, and even higher lacustrine terrace was found. The terrace with the same height as Heshangping continues to retain its remains in Shi Xia Canyon, so it can be inferred that Wanhe Lake in Gu Ni has an exit. At the bottom of Nihewan layer, local gypsum layer less than 1 cm can be found in some places, which may be the gypsum layer formed in the small lake separated by the lowering of the lake surface during drought. No obvious gypsum layer was found in the sediment in the middle of the lake, and these characteristics should be consistent with the existence of the lake outlet.
The third zone of sporopollen analysis in Dadaopo profile is roughly 0. 8 ~ 0.1Mab.p. Sporopollen types showed that woody plants decreased, herbaceous plants increased, elm, birch and pine pollen decreased, ephedra and Artemisia increased, and cattail and Cyperus pollen almost disappeared. The characteristics of sporopollen assemblage show that the climate is developing towards drought, which generally represents the temperate climate in semi-arid areas. Except for Xu Jiayao site, there are few ancient human sites in this period, which may be because the environmental conditions are not suitable for ancient human life, or because the investigation is not enough, and no Paleolithic sites in this period have been found.
(4) Late Pleistocene (0. 128 ~ 0.0 1 Mab.p .)
At the end of the middle Pleistocene and the beginning of the late Pleistocene, the eastern exit of Nihewan ancient lake became gentle due to the influence of tectonic movement, and the river cut down to make Nihewan ancient lake disappear. Lake sediments are eroded and flood alluvium accumulates on them. Aeolian loess (Malan loess) is accumulated on lacustrine platform. Although Nihewan ancient lake was replaced by Sanggan River, Sanggan River still provided necessary water resources for ancient humans.
There are many late Paleolithic sites in Nihewan Basin. At this time, the main body of the lake has disappeared, and most of the sites are found in terrace sediments. Mammalian fossils found in the site mainly include long-haired rhinoceros and wild horses. There are no fossils of forest grassland residents, which reflects the environment of arid grassland and desert grassland. Sporopollen analysis shows that the number of sporopollen is greatly reduced, conifers are the main woody plants, Artemisia and Ephedra are more common, representing a drier and colder temperate climate than the previous stage. However, the activities of ancient humans increased during this period, indicating that the production level of ancient humans who moved here at that time was greatly improved and their ability to resist harsh natural conditions was greatly strengthened. The natural conditions of ancient human life were similar to today's, but the ability and scope of human beings to use and transform nature were very small, and Sanggan River became an important water source and hunting area for ancient human beings.
(5) Holocene (1 1.5 thousand years ago).
The climate warmed in the early Holocene, but it was still not completely free from the cold and dry environment of the last ice age. Most vertebrate fossils in Hutouliang site are rodents, rabbits, odd-hoofed, cloven-hoofed and so on. But you can see the fossils of Palae-oloxodon namadicus, which shows that animals in subtropical areas can swim back here.
In the middle of Holocene, the climate of Nihewan Basin was suitable. Warm-loving animals live here, such as Indian elephants and primitive cows, as well as birds suitable for living by the water. Most mollusk fossils are species and genera that live south of the Yangtze River. It shows that the ecological environment in this period is similar to that in South China now. In the late Holocene, the climate turned to dry and cold, even reaching the present environment of arid grassland and shrub grassland.
To sum up, the quaternary climate environment of Nihewan rift basin is controlled by two important factors. First of all, the tectonic movement made this area a part of the Wei Fen Rift System, and the Quaternary neotectonic movement was active, and lakes existed for a long time. The other is the process of global climate change. Under the geomorphological and hydrological conditions of the rift basin in this area, every stage of global change and every climate event has a response, which together with tectonic movement controls the Quaternary environment in this area. Among them, the middle and late early Pleistocene (2. 0-0.8mab.p.) is the most critical. During this period, the global climate was relatively stable and no major climate events occurred. This area is dominated by arid grassland and forest grassland environment, and subtropical climate can appear in warm and humid climate stage. The lakeside area of Nihewan ancient lake has strong ecological diversity and is suitable for all kinds of herbivores and rodents to survive. Early hominids could get enough food in Nihewan Basin and thrive here. In particular, such ecological conditions can exist for a long time, enabling ancient humans to maintain long-term evolution here and continue to develop into more adaptive homo sapiens. Therefore, Nihewan Rift Valley Basin can be called the base or evolution laboratory of ancient human evolution in East Asia. The late hominids in East Asia may all be related to the early hominids in Nihewan rift basin, which is an important subject worthy of further study in the future.
In a word, Nihewan Basin experienced five environmental stages in Quaternary:
(1) 2.5 ~ 2.0 ma b.p. "Nangou cold period", no trace of ancient human activities was found.
(2) 2.0 ~ 0.8 Ma B.P., mainly in temperate environment, sometimes temporarily in subtropical environment, with rich vegetation and diverse animals, is the main period of ancient human activities here. Their activities are concentrated in the lakeside area, and the lake water is fresh water.
(3) From 0. Eight to zero. From 128 Ma ago, the arid temperate environment was drier and colder than the previous stage, but sites such as Maliang, Queergou, Wujialiang and Xu Jiayao were still found, showing the continuity of the survival and evolution of early ancient humans here.
(4) 0.128 ~ 0.01mabp.p., Nihewan ancient lake disappeared, Sanggan River appeared, and the climate was drier and colder than the previous stage. However, in ancient times, the level of human productivity improved and it was widely used on both sides of the Sanggan River.
(5) 0.1mab.p. Up to now, it has experienced the warm and humid stage of the Middle Holocene, and prehistoric civilization has been further developed. After 3,000 years ago, the climatic conditions were similar to today's, but the productivity of ancient humans was improved, and they were able to resist the harsh environment, which opened a new chapter in the history of ancient human development in China.