Why is dirt fun?

It was my first year as an archaeology student. I invited both old friends from school and new ones from university to my birthday party. Amazed by the extensive chit-chat about sediments, soils and excavating -and clearly also fairly bored- a non-archaeologist friend asked me: “Why do you guys like dirt so much?” Here, I will briefly show why dirt is fun -both for the layman and the obsessed archaeologist– with the explanation of the geo-toolkit, applied on a Javanese, Pleistocene site, containing important fossils in the study of human evolution.

Video field report - Why dirt is fun

Equipment in the geo-toolkit

Archaeology exploits methods and data from a variety of disciplines, such as anthropology, biology and history. Fundamental applications come from geology, since archaeology explores material remains in the ground. By taking the geological toolkit with into the field ‑both actual tools and mental tools— an accurate context of site formation, dating and (post)depositional processes can be provided. In other words, it helps us, archaeologists, to understand how and when finds ended up where we found them. The toolkit contains an infinite number of instruments, of which many are yet to be developed. A few of those tools in the geo-box include studying old and new geographical maps, geomorphological studies through coring, micromorphology, which investigates contents of sediments and soils, and geochemical isotope analysis, which uses patterned variation in elements on earth in order to reconstruct ecology in the past. 

A Javanese site in need of the toolkit

Eugène Dubois was the first researcher to discover and recognise Homo erectus fossils, which were found in 1984 at the site Trinil on the island of Java, Indonesia. Homo erectus can be considered an essential species in studying the emergence of the modern human body, brain and behaviour. The Dubois collection – which is curated at Naturalis (click for collection history (Dutch) and for an extensive description of the collection) contains a great variety of faunal fossils from the context and the whole region, thus providing the archaeological and ecological context of Homo erectus. However, since geology and archaeology were not yet well-developed, documentation quality and quantity lacks significantly. New excavations might improve our understanding of past and future finds at Trinil.

Sundaland, the biogeographical region that contains Java, is a biodiversity hotspot, caused by tectonic activity and climate dynamics throughout the Pleistocene. With warmer and colder periods, level rising and dropping hid or exposed shelves of the marine continent, which served as (resp.) barrier or bridges and corridors (dis)connecting mainland to islands. See for descriptions and reconstructions Semah et al. 2010 and Bird et al. 2005

The Trinil shells

An environmental reconstruction of Trinil, based on aquatic fauna from the Dubois collection indicated that Homo erectus lived in a coastal and riverine environment. In addition, an abundance of large bivalves at the main palaeoanthropological layer suggested hominin activities for gathering, dexterously opening and consuming molluscs. Moreover, on shell showed to be a retouched tool and a second shell contained a geometric patterns of groove zigzags on its exterior. All three finds are important in the discussion of developments human behaviour, including fish consumption – related to big brains and an associated required high-quality diet, aquatic resource use as raw material - and interesting addition to the debate on the Movius Line, and possibly even symbolic behaviour in species other than Homo sapiens.

Applying the toolkit

Historical documentation and modern maps

Re-evaluation of old documentation by Eugène Dubois and a comparison with modern data can allow for a general image of what to expect if new fieldwork will occur. Dubois’ original drawings were simplistic and of brief description. Modern accessible maps, such as ONEGEOLOGY, often relate to larger geographical areas in lower resolution. However, by cafefull combining the data, pointing out lacking information and detail in the geological knowledge of the site, might actually be useful and provide precise recommenations for future fieldwork. 

 

Dirty shells and their significance

The assemblage of bivalves that included the perforated molluscs’ exterior and the modified shells, included some left-over sediments, which were subjected to micromorphological analyses. Other sedimantary remains within the Dubois collection, a hominin skull and a Stegodon skull, allowed for comparisons of the residues. These indicated that the contents of these sediments, matrices and micro-concretions, are very similar in all three types of fossils. In addition, volcanic materials in the sediments allowed for the first direct dates of the site, pushing the original estimations back with 500.000 years, to a date of 0.45-0.54 ka. Finally, observations of thin sections provided for more information on the depositional character of the layer that contained these fossils. Absence of soil formation and bioturbation (disturbance by animals or plants) indicated a quick infill of the shells, thus a quick covering of the fossils, sealing it well-preserved.

Conclusions

Careful studying of dirt -either as described on maps, fresh from cores, or tiny bits on long-excavated fossils- can teach us where we come from and how human cognition evolved. Dirt provides context of archaeological sites, possibilties for accurate age determination of the first occurance of human traits, landscape formation details trought time and, most importantly, a pandora's box of possibilities to develop new tools to understand remains of our distance past.