Whatever Floats Your...Ancient Plant Remains: How Archaeologists Use Water to Help Sort Delicate Plant Remains

 This week we will look at how smaller plant material is recovered from an archaeological site, but first, it is important to understand that plant material is delicate and requires a specific set of environmental conditions for it to last in the soil. In most instances, an anaerobic environment will provide the best preservation. This is an environment that is lacking oxygen, and therefore lacks bacteria. Just like you and I, microscopic bacteria require oxygen, so there are less of them in an anaerobic environment. Without these little critters present, delicate plant matter isn't eaten away over time.

One of the most common plant remains found at sites is wood charcoal. Early people relied heavily on fire, and charcoal can be an important source of information. In fact, it is commonly thought that the lack of charcoal at a site is indicative of poor preservation, not the lack of fire during the site's occupation. Often larger pieces of charcoal are recovered during dry screening, which is the most common way to separate artifacts from soil. But how do archaeologists recover those little delicate bits that would slip through a dry screen? This depends on a variety of factors, from the type of plant remains found at the site, the research question, time constraints, budget constraints, and more.  But one of the most common ways to recover small bits of charcoal and other plant material (like seeds, or fruit pits) is using a process called floatation.

                                              Video of how floatation works (courtesy of 

                                                                  Science Friday) 

Floatation is using water to separate lightweight plant material from the soil through agitation, which allows the lightweight plant material to float to the surface. It is an efficient process that allows for rapid processing of a large quantity of material. There are a variety of types of floatation set ups, from DIY to commercially made machines. Again, the type used depends on a variety of factors and constraints. Floatation was first used in 1905 by German botanist , Ludwig Wittmack, to recover plant remains from adobe brick. But it was popularized in the 1960s after appearing in an archaeological publication written by Stuart Struever. Since then, floatation has become a staple for recovering delicate plant remains. It isn't perfect however, samples from very dry and arid climates sometime dissolve, but overall, it has helped archaeologists recover material that would otherwise remain a mystery, and thus has helped archaeologists piece together a more holistic view of the past.