Onset of extensive human fire use 50,000 y ago

Significance

Human mastery of fire in Quaternary played a pivotal role in early human evolution—improving dietary quality, enabling adaptation to cold environments, providing protection from predators, and shaping the social dynamics of our ancestors. Archaeological sites provide valuable insights regarding human fire use; however, their chronological gaps render the precise timing of large-scale fire utilization difficult to determine. Pyrogenic carbon deposited in marginal sea sediments, transported by major rivers traversing the continent, serves as a reliable proxy for continental-scale fire activity. By integrating pyrogenic carbon records with archaeological data, we propose that intensified human global expansion, population growth, and rising demand for fire use during cold glacials resulted in a surge in fire use since approximately 50,000 y ago.

Abstract

Fire is a pivotal aspect of human involvement in the carbon cycle. However, the precise timing of the large-scale human fire use remains uncertain. Here, we report a pyrogenic carbon record of East Asian fire history over the past 300,000 y from the East China Sea. This record suggests a rapid increase in fire activity since approximately 50,000 y ago, indicating a decoupling from the monsoon climate, and this pattern is consistent with fire histories in Europe, Southeast Asia, and Papua New Guinea-Australia regions. By integrating extensive archaeological data, we propose that the intensified global expansion of modern human and population growth, coupled with the rising demand for fire use during cold glacial periods, resulted in a significant increase in fire utilization from 50,000 y onward. This suggests that a measurable human imprint on the carbon cycle via fire likely predates the Last Glacial Maximum.

Fire is a natural phenomenon within the Earth System that began in the Silurian Period and has had profound influences on vegetation evolution, animal behavior, and the Earth’s carbon cycle (1–3). For hundreds of millions of years, fire has been dominated by bioclimatic factors such as vegetation, temperature, and rainfall. However, in the Quaternary, humans gradually began using fire and became a significant factor in fire occurrence and spread (4). The use of fire indirectly facilitated the evolution of early humans by improving their diet, enabling them to adapt to freezing temperatures, and providing protection against wild animals. Concurrently, this evolution also facilitated the development of technologies for using fire to make tools (2, 5–8). Archeological and genetic evidence suggests that the strong interactions among different human groups, which have occurred since the Middle Pleistocene (9, 10) (Fig. 1A), may have contributed to an increase in both the sophistication of fire-related technology and the frequency of human fire use (4, 11). Studies on the history of human fire use have largely focused on archaeological sites (12). However, the chronological frameworks of these sites are intermittent, posing challenges in obtaining continuous and high-resolution records of human fire use throughout history. As a result, the precise timing of when humans began to use fire on a large scale remains elusive.

Fig. 1.

Climatology, fire activity in East Asia, and late Pleistocene dispersal of Homo sapiens. (A) H. sapiens dispersal routes from Africa to Eurasia (9). (B) Map of the study area and location of IODP Site U1429. The gray and blue dashed lines, respectively, show the coastline and paleo-river channels across the exposed continental shelf during the Last Glacial Maximum (13). Arrows show the East Asian summer monsoon (EASM, red) and East Asian winter monsoon (EAWM, blue). White triangles denote the locations of Chinese speleothem records. (C) Modern seasonal variations of fire activities (14) and climate (National Oceanic and Atmospheric Administration, National Centers for Environmental Information) in the northern East Asia.

Pyrogenic carbon in sediments, produced by incomplete combustion of biomass by wildfires and burning of fossil fuels (15, 16), has the potential to reconstruct the continuous historical evolution of fire altered by human activity (2, 17–20). It can persist in sedimentary environments for a long time and is thus associated with negative feedback in the carbon cycle (21). Pyrogenic carbon emitted from fire can be transported to the ocean via wind or river processes (22), and when deposited in marginal sea sediments, it can largely reflect continental-scale fire activity, especially when transported by major rivers that traverse the continent (23). Detailed fire histories in Asia–Australia regions have been successfully reconstructed using pyrogenic carbon records in marine sediments, indicating the influence of climate and human interactions on local fire activity (17, 24–26). Here, utilizing the pyrogenic carbon record from sediments at Integrated Ocean Drilling Program (IODP) Site U1429 in the northeastern East China Sea (Fig. 1B), we reconstructed the fire history of northern East Asia over the past 300 kyr. Our findings indicate that monsoon rainfall was a dominant factor in fire activity before ~50 ka, but since then, fire rapidly intensified, coinciding with evidence of fire histories in Europe, Southeast Asia, and the Papua New Guinea-Australia regions. We propose that the intensified human global expansion and population growth, coupled with the rising demand for fire use during cold glacial periods, resulted in a significant increase in fire utilization since 50 ka.

Results

Reconstruction of Fire History in Northern East Asia.

The pyrogenic carbon content in the sediments of Site U1429 ranges from 0.04 to 0.3%. From 300 to 50 ka, the long-term trend in pyrogenic carbon content remained relatively stable, with an average content of approximately 0.13%. However, since 50 ka, a rapid increase in pyrogenic carbon content has been observed, with the average value rising to about 0.2%, nearly doubling compared to that before 50 ka (Fig. 2A). The pyrogenic carbon flux also exhibits a similar trend compared to the content (Fig. 2 A and B), with an average value of approximately 34.8 and 66.7 g/cm²/kyr before and after 50 ka, respectively.

Fig. 2.

Comparison of pyrogenic carbon records with climate changes since the last 300 ka. (A–C) Pyrogenic carbon content, flux, and carbon isotopes (Dataset S1). The green vertical bar, gray, and red dashed lines represent the results of a breakpoint regression, which indicates distinct values of R-squared and, consequently, a significant shift in pyrogenic carbon content and flux before and after 50 ka. (D) LR04 stacked benthic δ¹⁸O curve (27). Gray vertical bars show the glacial termination and designated Marine isotope stage (MIS) nomenclature also follows (28).

Variations in the pyrogenic carbon content and flux in marginal sea sediments can be attributed to the provenance, transportation and sedimentation processes, vegetation type, and fire intensity changes. A prerequisite for reconstructing fire history using pyrogenic carbon is determining their source areas (17). Due to its high adsorption capacity, pyrogenic carbon in soil and river sediments can be adsorbed onto the surface of surrounding minerals for transportation. Consequently, pyrogenic carbon in marine sediments undergoes a source-to-sink process similar to terrestrial materials (29). Previous source tracing of the U1429 sediments using Sr-Nd-Pb isotopes, rare earth elements, and clay minerals has suggested that the sediments, and consequently the pyrogenic carbon, were primarily sourced from the Yellow River in northern East Asia (13, 30, 31). Eolian dust is also an important carrier of pyrogenic carbon in marine sediments (8), but the influence of eolian dust-transported pyrogenic carbon is minor in the East Asian marginal sea (17), where sediment composition is dominated by the riverine input from the continent (30, 32).

There is no significant correlation between the pyrogenic carbon content and grain size, suggesting that sorting effect during sediment transport is relatively minor (SI Appendix, Fig. S1 A and C). Furthermore, no apparent synchronous variation was observed between pyrogenic carbon content and sea level change, indicating that the impact of sea level fluctuations and associated estuarine movements during glacial-interglacial cycles on pyrogenic carbon levels can be ignored (SI Appendix, Fig. S1 A and D). By contrast, since pyrogenic carbon flux incorporates information about both pyrogenic carbon content and linear sedimentation rate, it exhibits a certain correlation with grain size and sea level change (SI Appendix, Fig. S1 B–D). During glacial low sea level stages, the development of paleo-river channels on the exposed continental shelf resulted in the proximity of river outlets to the study site (Fig. 1B) (29), which led to relatively higher pyrogenic carbon flux during glacial periods. However, such sea level effects cannot fully explain the exceptionally high flux after 50 ka. The steep decline of pyrogenic carbon flux since the early Holocene was largely resulted from the decreased sediment flux caused by sea level rise and the large-scale landward migration of the river mouth to its present position (Fig. 1B and SI Appendix, Fig. S1D).

Pyrogenic carbon originates from the burning of terrestrial plants, which absorb atmospheric CO₂ through photosynthesis to synthesize their own organic matter (22). The stable carbon isotope distribution ranges for C3 and C4 plants vary significantly, with values of approximately −37 to −20‰ for C3 plants and −15 to −9‰ for C4 plants, respectively (33, 34). Consequently, the δ¹³C record of pyrogenic carbon in the sediments of the Asian marginal sea has been widely applied as a reliable tracer of terrestrial C3/C4 ecosystem evolution (35–38). Our pyrogenic carbon δ¹³C record indicates that the C3/C4 vegetation evolution in northern East Asia varied with glacial–interglacial cycles, with an expansion of C4 vegetation coverage during colder glacial periods (Fig. 2C). Since around 50 ka, there was no significant transition in vegetation compared with that during previous intervals. This is inconsistent with the observed rapid increase trend in pyrogenic carbon content and flux, suggesting that the C3/C4 vegetation type was not the primary factor responsible for the rapid increase in pyrogenic carbon production. Therefore, we propose that the pyrogenic carbon content and flux in the sediments at Site U1429 can serve as reliable proxies for reconstructing the fire intensity history in northern East Asia.

Discussion

Monsoon Climate-Controlled Fire in Northern East Asia before ~50 ka.

Prior to human mastery of fire, its occurrence was primarily governed by bioclimatic factors such as the availability and type of burnable biomass, temperature, and moisture conditions (4). Climate factors, including temperature and rainfall, not only determine the conditions under which fires occur but also influence the abundance, composition, and structure of available fuels (39). Enhanced precipitation and high environmental humidity can inhibit fire activity, but increased humidity also promotes vegetation growth, providing abundant fuel for fires. Consequently, rapid transitions between wet and dry conditions have the potential to promote fire occurrences (1, 17). In arid and semiarid regions, increased precipitation favors local vegetation growth, which in turn increases fire activity (40). Conversely, in humid climatic zones, enhanced precipitation promotes environmental humidity, which can suppress fire occurrences (41, 42).

In the East Asian monsoon region, pronounced seasonality and rapid transitions between wet and dry conditions are key factors influencing fire activity. Modern fire observations reveal that fire activity in this region exhibits seasonal variation, with lower frequency in wet summers and higher frequency in drier springs and autumns (14, 43) (Fig. 1C), suggesting the strong control of monsoon rainfall. Our reconstructed fire history of northern East Asia exhibits an overall inverse relationship with monsoon rainfall, indicating high fire intensities during periods of weakened rainfall associated with precession maximum conditions from 300 to 50 ka (Fig. 3 A–C). This suggests that abundant summer monsoon rainfall is less conducive to the occurrence of wildfires compared to arid environments. Additionally, other pyrogenic carbon records from the Chinese Loess Plateau in northern East Asia also indicate more frequent wildfire occurrences during drier climate periods (44–46). We propose that the monsoon climate played a dominant role in fire activity in northern East Asia from 300 to 50 ka. During this period, it is likely that the relatively small population, as indicated by the number of archaeological sites, resulted in less fire use (Fig. 3D), resulting in minimal human impact on fire activity in the region.

Fig. 3.

Comparison among northern East Asian fire, climate, and archaeological sites. (A) Chinese stalagmite δ¹⁸O record (47). (B) Reconstructed and simulated northern East Asian rainfall (48). (C) Pyrogenic carbon content and flux in sediments of IODP Site U1429. (D) Latitude distribution of East Asian archaeological sites throughout the last 300 kyr (Dataset S2). (E) The timeline of human dispersal in Eurasia (9). (F) LR04 stacked benthic δ¹⁸O curve (27) and designated MIS nomenclature also follows (28). Gray vertical bars show the precessional variation among different proxies. Vertical bars with color gradients denote the enhanced fire activities in correspondence to increased archaeological fire sites.

Human-Controlled Fire in Northern East Asia since ~50 ka.

In contrast to monsoon rainfall patterns, fire activity in northern East Asia has exhibited a pronounced long-term increase since ~50 ka (Fig. 3 A–C). This decoupling indicates that the monsoon climate no longer directly drives local fire activity. Rather, the global expansion of anatomically modern humans, interacting intensively with East Asian indigenous populations beginning around 50 ka, presumably triggered the emergence of large-scale fire use in this region. (7, 9, 49). During the middle Marine isotope stage (MIS) 3, there were more pronounced changes in the diversity of technological behaviors and cultures among humans in northern East Asia (50, 51). Modern human entered the hinterland of northern China during this period, and more importantly, there was also strong local integration and innovation in tool making and fire technology (52). It has been reported that the stone tools at the Shiyu site in northern China exhibit both characteristics of the technological system from the western side of Eurasia and the tool-making concepts of East Asia, suggesting frequent human migration and interactions during this stage (53). Sites such as Laonainaimiao and Xiamabei in the northern China all show evidence of living spaces around fire pits, reflecting improvements in human fire use capabilities and the development of spatial utilization abilities (54–56).

The number of archaeological sites in the northern East Asia indicates significant population growth since approximately 50 ka (52, 54, 56) (Fig. 3D), which coincides with the pronounced increase of fire activity as reflected in our fire records. This indicates that the intensified control of humans, which overwhelmed the influence of the monsoon climate, became the dominant factor shaping fire activity. Nevertheless, enhanced fire activity occurred also during periods of intensified monsoon rainfall under precession minimum conditions around 50 to 46 ka, 36 to 28 ka, and 17 to 10 ka (Fig. 3 B and C). This is inconsistent with the relationship between fire and monsoon climate observed before approximately 50 ka (Fig. 3 B and C). This can be attributed to the fact that enhanced monsoon rainfall promoted human expansion, integration, and societal prosperity (57–59), which in turn led to an increase in the frequency of fire activity.

Onset of Extensive Human Fire Use since ~50 ka.

In addition to our reconstruction of East Asian fire history, the number of archaeological fire sites in Europe, and the pyrogenic carbon records from Sulu Sea, Caroline Basin north of Papua New Guinea, and northeastern Australia collectively reveal a pronounced increase in fire activity after ~50 ka (25, 26, 60, 61) (Fig. 4 A and E–H). Furthermore, variations in pollen taxa can also reflect fire activity. Pollen records of Keteleeria and Podocarpus in the middle Okinawa Trough, Artemisia and Pinus in the South China Sea, and Eucalyptus in northeastern Australia all exhibit elevated concentrations since ~50 ka, which were markedly different from their relatively low contents and stable trends observed during the previous glacial–interglacial cycles (60–63) (Fig. 4 C, D, G, and H). Enhanced fire frequency may create a broader landscape for these taxa to thrive (64). Additionally, recurrent fires play a crucial role in shaping the age structure and serve as essential ecological processes for maintaining fire-adapted species of Artemisia, Pinus, and Eucalyptus (65, 66). Thus, the large-scale increase of pollen content of these species after ~50 ka was very likely to indicate the enhanced fire activity. Besides, pollen analysis of the archaeological sequence from Niah Cave in Southeast Asia indicates an increased presence of Justicia, a fire-favored taxon associated with lush forest phases, suggesting enhanced biomass burning by humans to maintain forest-edge habitats at ~50 ka (67). Such coherent increased fire activity across Europe, East Asia, Southeast Asia, and Australia reveals that this is not limited to local regions but reflects a major shift across entire continents.

Fig. 4.

Comparison between fire history of Europe, East Asia, Southeast Asia, and Papua New Guinea-Australia regions and archaeological sites. (A) Number of sites with good evidence of fire in Europe per 10 kyr (11) (B) Pyrogenic carbon record at IODP Site U1429 (this study). (C) Pollen record at MD98-2194 (63). (D) Pollen record at ODP Site 1144 (62). (E) Pyrogenic carbon record at MD97-2141 (25). (F) Pyrogenic carbon record at MD97-2140 (26). (G) Pyrogenic carbon and pollen records at Lynch’s Crater (60). (H) Pyrogenic carbon and pollen records at ODP Site 820 (61). (I) Age distribution of archaeological sites of Africa, Eurasia, and Australia since the last 300 kyr.

The growing number of archaeological sites in Africa, Eurasia, and Australia indicate that the human global expansion and population growth, coupled with the increasing demand for fire use during cold glacial periods, likely contributed to the rise in human use of fire across these vast landmasses since ~50 ka (Fig. 4I). The Late Pleistocene was a crucial period for the global expansion of modern humans, a process that not only facilitated rapid population mobility but also the diffusion of diverse cultural and technological factors, ultimately leading to new behavioral changes. Modern humans may have migrated in two waves from Africa to Eurasia and Oceania, integrating with local populations during the late Pleistocene, potentially resulting in the exchange of ideas, technologies, and genetic material (68). The earlier expansion occurred around 120 ka (Fig. 3E) (9, 69). This interglacial warm climate and relatively abundant food supplies facilitated population migration, enabling early modern humans to reach West Eurasia, interbreed with Denisovans, and subsequently migrate to South Asia, East Asia, and Oceania (9). During this period, evidence for human fire use slightly increased compared to previous stages, reflecting relatively intensified fire use in this phase (11). An increased number of archaeological sites with good evidence of fire have been discovered in Europe and East Asia during MIS 5 (11, 70–73).

The later human expansion took place during the glacial period around 60 to 45 ka (Fig. 3E) (9). Based on genetic and paleoanthropological evidence (7), the scale of human migration out of Africa during this period was significantly greater than that which occurred during Marine Isotope Stage 5. This can also be seen in the rapidly growing number of archaeological sites since ~50 ka (Fig. 4I). The cold climate and food shortage led humans to expand in search of more living space and resources, as well as to increase the use of fire. During this time, low sea levels and the exposure of continental shelves created favorable conditions for human dispersal across Eurasia and Oceania (74–76). The colder climate caused the reduction of tropical rainforest barriers, resulting in vast grasslands that facilitated migration (77). Additionally, the exposed continental shelves had broader vegetation coverage and supported more wildlife, which were essential for humans relying on foraging and hunting (76). Under such conditions, modern humans rapidly spread from North Africa to Europe, East Asia, Southeast Asia, and eventually throughout the world (7, 9, 78–80). They gradually replaced the archaic human species including Neanderthals in Europe and the Near East, and Denisovans in East Asia (81). During this period, numerous archaeological sites with compelling evidence of fire utilization have been discovered. The number of archaeological fire sites in Europe during MIS 3 was four times that during MIS 5 (11). Archaeological evidence from East Asia suggests widespread fire use, as evidenced by hearth remains found at multiple sites in northern, central, and southern China, such as Hutouliang, Zhijidong, Dahe, Shuidonggou, Xishan, and Shizitan, providing rich insights into fire management during this period (56). In Southeast Asia, pollen and charcoal records from Niah Cave and Tam Pà Ling, respectively, show an increased biomass burning by humans during MIS 3 (67, 82). Archaeological fire sites in Australia, including Riwi Cave (83), Devil’s Lair (84), Lake Mungo (85), and records from the islands of Bass Strait (86), indicate a timing of increased human use of fire that coincides closely with the arrival of modern humans in the continent around MIS 3 (87). This aligns with pollen and charcoal records from Australian lakes and surrounding oceans (88). Despite ongoing debates about the timing of the human start to modify local fire (89) and whether climate or human activity primarily influenced fire regimes (90) in Australia, the consistent timing of increased human archaeological site density, along with the emergence of fire sites, corresponds well with the enhanced fire activity indicated by most of the marine pollen and charcoal records. This indicates that humans in Australia were very likely to begin to utilize fire on a large scale during this time period. The debate regarding the timing likely originates from spatially heterogeneous population distributions (91) (Fig. 4I), which would result in regionally discordant fire histories preserved in the records.

Collectively, we propose that the global expansion and population growth of humans, as well as glacial cold environment contributed to intensifying human fire use since ~50 ka. As a critical technological adaptation, fire probably served as both a survival tool and a competitive advantage in interactions between modern human and indigenous groups (92). This strategic application of fire would have enhanced resource acquisition and habitat modification, thereby further supporting population growth and cultural prosperity amid the climatic stresses of the glacial environment.

Materials and Methods

Site Location and Age Model.

IODP Site U1429 (31°37.04′N, 128°59.85′E) is located on the western continental slope of northeastern East China Sea at a water depth of 732 m (93). At this site, three holes were cored to a composite depth below the seafloor (CCSF-D) of 200 m. The lithology of the section recovered from the study site is mainly composed of calcareous nannofossil ooze and calcareous nannofossil-rich clay, with tephra layers and minor dispersed volcaniclastic materials throughout the succession (93). The age model was developed by correlating the δ¹⁸O record obtained from benthic foraminifera with the global benthic stack (94).

Pyrogenic Carbon Analysis.

In this study, pyrogenic carbon was extracted from the sediments of U1429 using the chemical oxidation method proposed by Lim and Cachier (95). This method has been widely applied in research on pyrogenic carbon based on marine and lake sediments (17, 18, 25, 26, 35, 96).

First, 1 to 2 g dried bulk sediments were treated with HCl to remove carbonates. Then, the silicate minerals and refractory oxides were sequentially dissolved by HF+HCl and HCl, respectively. Finally, the acid-treated samples were oxidized by a mixture of K₂Cr₂O₇ and H₂SO₄ to remove organic matter and kerogen. Repeated process of centrifuge and rinsing was performed after each step. The remaining refractory carbon left in the residue was operationally defined as pyrogenic carbon (17, 35).

The pyrogenic carbon content and carbon isotopic compositions were measured using a Thermo Elemental Analyzer (FLASH 2000) coupled to a Thermo Finnigan Mass Spectrometer (MAT 253) at the Yantai Institute of Coastal Zone Research, Chinese Academy of Science (17, 24). The pyrogenic carbon abundance is expressed as percentage (%). The carbon isotopic compositions were expressed in conventional delta (δ) notation as deviations from the standard Vienna Pee Dee Belemnite. To monitor the working conditions, duplicate analysis of standard samples (high Organic Sediment Standard OAS-Certificate no.162517, δ¹³C = −26.27‰, certified value for carbon content is 9.15%) was performed every 10 samples, yielding a precision of ±0.2‰ for δ¹³C values. Additionally, the measured pyrogenic carbon content was converted to the original sample’s pyrogenic carbon content (the real value) using the following formula: C0 = C1 × M1/M0. C0 and C1 represent the original and measured pyrogenic carbon content, respectively. M0 and M1 are the mass of the sample before and after treatment, respectively. The pyrogenic carbon flux was calculated by multiplying the pyrogenic carbon content by the mass accumulation rate (93).

Morphology and chemical composition of extracted pyrogenic carbon particles were also investigated by scanning electron microscopy–energy dispersive spectroscopy (SEM-EDS) (SI Appendix, Fig. S2) (17, 35). The residues remaining after the chemical extraction process described above were placed on a slide, which was then mounted onto the conductive tape holder. Subsequently, the sample was gold-coated and analyzed by SEM-EDS (JSM IT-800) at the Institute of Oceanology, Chinese Academy of Sciences. These results reveal a predominance of carbon in the chemical composition of the extracted particles, consistent with pyrogenic carbon formation through biomass combustion.

Dataset of Archaeological Fire Sites.

The archaeological site dataset comprises 247,023 data entries, confined to the temporal age interval of approximately 300 to 0 ka (Dataset S2). It includes site names, geographical coordinates, and references. This dataset is derived from compilations of archaeological sites, including the XRONOS database maintained by Martin Hinz and Joe Roe at the Institute of Archaeological Sciences, University of Bern, the Human Origins Locality Data Collective database supported by Henry Gilbert from California State University, East Bay, and the dataset collected by ref. 2.

Supplementary Material

Appendix 01 (PDF)

Dataset S01 (XLSX)

Dataset S02 (XLSX)

Data, Materials, and Software Availability

All study data are included in the article and/or supporting information.