BIOMARKERS & ARCHAEOLOGY
The archaeological and paleoanthropological applications of various biomarkers are wide and diverse.
BIOMARKERS
A schematic diagram of leaf anatomy highlighting the location of the plant wax lipids. A. A dumb cane (Dieffenbachia seguine) leaf with a reflective waxy surface. B. A scanning electron micrograph of the cross section of a leaf: (1) Upper epidermis covered by a cuticular membrane with epicuticular wax deposits on its outer surface visible (white arrow). (2) The lower epidermis covered with a cuticular membrane but with fewer epicuticular wax deposits (black arrow). A stoma is shown near center. (3) Mesophyll. Original leaf scanning electron microscope image provided by Dr. Qin Leng, Bryant University. Figure from Patalano et al., 2021. Evolutionary Anthropology.
Biological marker molecules, or biomarkers, are complex organic compounds composed of carbon, hydrogen, oxygen, and other elements that originate from formerly living organisms. They provide information on the type and amount of organic content preserved within source rock or sediment, the organisms that produced them, environmental conditions during deposition and burial, and the degree of degradation of the original biological components. Traditionally used in earth sciences and climate studies from ‘off-site’ ocean and lake records, biomarker research is now incorporated in archaeology and paleoanthropology to answer questions relating to past human-environment interactions and human evolution.
In my research, I have largely focused on plant wax biomarkers, an innovative proxy for reconstructing vegetation composition and structure, rainfall intensity, temperature, and other climatic and environmental dynamics. The external surface of leaves and other plant parts are coated with protective waxes that help preserve the water balance of the plant and minimize damage to leaf cells from fungal and insect attack, wind abrasion, and excessive ultraviolet radiation. These waxes record environmental conditions in their compound distributions, abundances, and carbon and hydrogen isotope ratios. Plant wax lipids are readily dispersed through the environment and, due to their hydrophobic behavior, are well-preserved in a variety of soil, lake, and ocean sediments. When recovered directly ‘on-site’ in archaeological trenches, cave or rock shelter deposits, and hominin- and stone tool-bearing sediments, biomarkers provide well-integrated, high-resolution data on past climatic, ecological, and environmental conditions in areas where human activity occurred.
APPLICATION OF BIOMARKERS TO ARCHAEOLOGY AND PALEOANTHROPOLOGY
As a Postdoctoral Research Fellow in Palaeoenvironmental Biomarkers at the Max Planck Institute for the Science of Human History, I use stable carbon and hydrogen isotopes from archaeological sediments to answer questions concerning the relationships between environmental processes, cultural change, and human evolution. My active research involves the analyses of biomarkers and stable isotopes directly from archaeological- and paleontological-bearing sediments to address major questions on hominin adaptability to their diverse and variable past habitats. I collaborate on projects that are helping to define the paleoecology of both the earliest Oldowan and Acheulean known from Oldupai Gorge, Tanzania; Homo sapiens highland and tropical forest resilience in Lesotho and Kenya, respectively; the environmental and hydroclimate history of Upper Palaeolithic human dispersals in the southern Zagros Mountains of Iran; and the evidence, or lack thereof, of a Late Pleistocene ‘Savanna Corridor’ in Southeast Asia. My research has not been restricted to the Pleistocene however, as I have led projects studying the environmental and hydrological conditions of early rice domestication in eastern China and Great Wall building phases in the Han Dynasty’s northwestern frontier. Additionally, I perform modern ecosystem isotope calibration studies for use as ecological baselines to help interpret observations in paleo-records.
As a postdoctoral fellow, I am leading or collaborating on a number of archaeological and paleoanthropological projects that incorporate plant wax biomarkers into their research questions. These projects geographically span eastern, southern, and western Africa, the Middle East, east and southeast Asia, and western Europe, and temporally covers the past two million years.
PROJECT HIGHLIGHTS
The Environmental Context of the Earliest Known Oldowan and Acheulean from Oldupai Gorge, Tanzania.
The n-alkane δ13C data from FLK-W is plotted against total number of recovered lithics and bones with identifiable cut or percussion marks in the right panel. The total number of lithics and bones correlate with woody vegetation cover as indicated by δ13C. As the landscape becomes more open, the number of lithics and bones drops significantly. Right panel figure from Patalano et al., 2021. Evolutionary Anthropology.
The top left panel shows fossilized starch granules recovered in ancient residue from an Acheulean handaxe excavated at FLK-W. The blue and green EDX (Energy Dispersive X-ray spectroscopy) demonstrate a carbonaceous compound that underwent permineralization. From Mercader et al., 2017. EAAPP.
As a PhD student, postdoctoral researcher, and member of the Stone Tools, Diet, and Sociality project, I have been working at Oldupai since 2014. My dissertation research focused on the ~1.7 million year old FLK-W site and the plant ecology of Oldupai’s earliest known Acheulean. I compared this dataset to samples collected from off-site geological outcrops and from the FLK-N site, a 1.8 million year old Oldowan locality. I utilized the compound distributions and carbon and hydrogen isotope ratios of both normal (n-) alkanes and n-alkanoic acids to study the environmental and hydroclimate settings of the “transition” from the Oldowan to the Acheulean and the (intra)biome diversity of the plant landscape surrounding paleo-lake Oldupai. At FLK-W, Acheulean tool use and hominin butchering of animals occurred in wooded habitat, likely a riparian woodland or gallery forest. Hominin activity reduced and then stopped once the woodland opened up and became grass-dominated. Interestingly, Acheulean handaxes from the site were not used for defleshing or disarticulation of carcasses, but conceivably used for digging underground storage organs/tubers.
I am also involved in excavations and paleo-reconstructions at the Ewass Oldupa site, where the earliest known Oldowan (~2 million year old) from Oldupai Gorge has been found. (“Ewass Oldupa” is Maa, the Maasai language, for ‘the way to Oldupa’ or ‘the way to the gorge.’) Early Oldowan tools from the site reveal that homogenous technology was utilized within diverse, rapidly changing environments that ranged from fern meadows to woodland mosaics, naturally burned landscapes, lakeside woodland/palm groves, and hyper-xeric steppes. The early Oldowan stone tools were used in diverse physical environments, with indications that these environments both changed significantly over space and time, a finding that depicts complex behavior among early Pleistocene hominins.
Quartzite spheroid from Ewass Oldupa. Image from Mercader et al., 2021. Nature Communications.
Why this matters: Although archaeologists have been studying the Oldowan and Acheulean for decades, we still are not 100% sure what caused their emergence and widespread use in the Pleistocene. Obviously these tools were used for acquiring plant and animal food resources but we do not know if their appearance in the archaeological record was driven by environmental conditions, the emergence of new species, or something else. By using plant wax biomarkers in combination with other proxies to reveal the ecological settings of the earliest known Oldowan and Acheulean from Oldupai Gorge, we add to this debate and show that in the case of the Oldowan, the environment was not a factor in tool-use behavior as hominins utilized the same tool types in diverse, rapidly changing settings, whereas for the Acheulean, wooded habitats acted as an “ecological magnet” or focal points on the landscape for hominin activity.
Hydrological Changes Facilitated Early Rice Farming in Eastern China
High-resolution n-alkane carbon and hydrogen isotope record of the Tianluoshan area between 7.0 and 4.6 thousand years ago, with comparative data of grass phytolith concentrations. From Patalano et al., 2015.
Before my PhD and formal training in Stone Age archaeology, I worked as a laboratory manager and research assistant in the Laboratory for Terrestrial Environments at Bryant University. I was fortunate enough to travel and do some fieldwork in China, and lead a project using biomarkers from sediments collected at one of the earliest rice farming sites in the country, Tianluoshan. In this study, we generated a high-resolution n-alkane carbon and hydrogen isotope dataset spanning a five thousand year period at the Tianluoshan archaeological site in China’s eastern coastal region. Combined with micropaleontological records, our dual isotope data revealed a detailed hydroclimate profile from 7.0 to 4.6 thousand years ago, showing major hydrological changes coinciding with the early development of rice farming in the lower Yangtze region. We observed two major drought events and regional sea-level changes that opened suitable new habitats for expanding rice agriculture in the lower Yangtze Delta when subsequent humid climate regimes returned.
Why this matters: Rice is one of the world's most important cereal crops and feeds billions of people annually. It can be grown in a wide range of climatic conditions, from river deltas to mountains, and is a staple component of dietary cultures around the world. However, many researchers focused on the domestication of important plant species, rice included, disagree on where, when, and how many times humans domesticated wild rice to create the world's most important crop. Although our paper does not speak to the origins of rice domestication roughly 8000 years ago, it does show the environmental conditions that helped facilitate the expansion of rice farming in eastern China. Prior to this study, detailed climate records associated with critical periods of the development of early rice farming were lacking.
Ancient Great Wall Building Materials Show Localized Environmental Conditions in Northwestern China
Plant material used in the construction of the Han Dynasty Great Wall in northwestern China contain untapped potential for revealing paleoenvironmental conditions at individual wall segments and beacon towers. In the first ever study of this nature, we characterized the molecular preservation and stable carbon and nitrogen isotope compositions of common reeds used in the original construction of the Great Wall dated to the Han Dynasty in today’s Gansu and Xinjiang provinces. Our data demonstrate that ancient reeds were harvested from local habitats that were more diverse than exist in this region today, while also showing differential rates of environmental deterioration along this important route of the Silk Road. There is a wealth of environmental and climate information obtainable from site-specific organic building material of ancient walls. This paper is currently in review.
Why this matters: Many people are familiar with the iconic brick and stone masonry walls of the Ming Dynasty. But these actually developed out of an extensive system of fascine and rammed-earth walls, beacon towers, and fortifications that helped expand the western frontier of the Han Empire from the central plains of China into today’s Gansu Province and Xinjiang Uyghur Autonomous Region as early as the 2nd century BC. The Han era walls still contain organic remains that can be used as a source for biomarkers, but also for radiocarbon dating and paleobotany analyses. This is the first study to show the potential of these organic remains in archaeological sciences.
Two sections of the Great Wall. The Ming Dynasty brick and mortar wall (left) and the Han era reed-fascine and rammed-earth wall (right). Ming Wall photo taken by Robert Patalano. Han wall photo provided by Dr. Hong Yang.
Ongoing Projects
As mentioned above, I am actively involved in a number of ongoing projects, some of which currently have publications in review. For example, we just submitted a modern baseline study that uses both compound specific and bulk carbon isotopes to look at how temperature variations linked to altitude and aspect produce sharp gradients of C4 to C3 vegetation across three topsoil transects between 1,800 and 3,000 m a.s.l in eastern Lesotho, southern Africa. For the most part, the bulk and compound specific data show similar patterns correlating with elevation change. However, bulk carbon values suggest a greater input of C4 plants in some locations, but it is possible that the bulk measurements are recording non-terrestrial plant carbon biosynthetic sources, such as bryophytes. This paper is currently in review.
Among the least investigated regions of hominin expansions across Asia is the Iranian Plateau, a key potential dispersal corridor with connections to Southwestern Asia. Another project I am contributing biomarker analyses to is at Pebdeh Cave, which provides new information about the timing and context of Late Pleistocene hominin expansions in the Zagros Mountains of Iran. Stable isotopes of plant biomarkers from archaeological cave sediments reveal that vegetation and hydrological conditions remained relatively stable throughout Marine Isotope Stage 3 (~42 thousand years ago) during Middle Stone Age occupation. This paper will be submitted for review soon.
The Late Pleistocene ‘Savanna Corridor’ of Southeast Asia remains hotly disputed in archaeology, paleoanthropology and paleoecology. Modelled arid conditions heading into the Last Glacial Maximum have been frequently associated with an expansion of grassland through Sundaland and Wallacea at the expense of tropical forests, providing a crucial conveyor belt for large animals, including our own species, to move through the region. In this study, we compare pollen, sediment, and faunal isotopic records to test for the presence of grassland biomes in the Late Pleistocene. We argue that rather than ‘savanna’ corridors, a seasonal forest may have been the dominant ecological setting for dispersal in the region. The manuscript for this project is current in preparation.