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There are several dating methods that help archaeologists figure out how old objects are. In fact, there are so many that it would be impossible to describe them all in one article. Hence, this post will discuss some of the most widely-used dating methods — stratigraphy, typology, seriation, and radiocarbon dating — and we will cover the rest in subsequent articles. There are two overarching classes of dating methods: relative and absolute. Relative dating methods cannot determine the exact age of an object, but only which finds are older or younger than others.
When excavating an archaeological site, you can literally see the layers of dirt and debris that have accumulated over time. Thus, objects found near the top of a site are probably younger than the ones further down — unless something like a burrowing animal moved the items after burial. Other relative dating methods depend on examining the physical characteristics of archaeological finds. In a given culture — or amongst connected cultures — artifacts with similar styles typologies tend to be popular at specific times.
While studying the typologies of archaeological remains allows researchers to figure out which objects are close in age, seriation helps them track cultural trends. Let me explain seriation through a hypothetical example. For instance, assume that archaeologists working in a given site have found the remains of many ceramic bowls that have distinctive, horizontal bands along their lips.
By recording the stratigraphic layers in which they uncovered the bowls, the archaeologists noticed that they found a few bowls in the oldest layers of their site, lots of them in the middle layers, and then just a handful in the most recent layers. Many assemblages, or groups of similar artifacts, go through this pattern: they emerge, rise to their peak in popularity, and then fade away. Here is a seriation diagram involving different types and time periods of tombstones at Old City Cemetery in Vancouver, Washington, where the data is laid out in the classic battleship curve pattern.
Public domain photo, credits to the National Park Service. By tracking the battleship curves of different assemblages of artifacts, archaeologists can observe the evolution of past technologies over time. Absolute dating methods can attach specific years to archaeological finds.
More specifically, they provide ranges of possible years, because no absolute dating method is exact — with the possible exception of dendrochronology tree ring dating. Each absolute dating method also requires a different kind of sample, which means that not every method can be used on each site. The most commonly-used absolute dating method needs carbon-based samples. Radiocarbon dating was developed in the s by chemist Willard F.
Plants absorb 14 C through photosynthesis, and animals consume it by eating plants or other animals. When plants and animals die they stop acquiring 14 C. Since 14 C is mildly radioactive and naturally decays into 12 C, plants and animals slowly lose their 14 C after they stop obtaining it. Fortunately for archaeologists, 14 C decays at a uniform rate. It takes years for half of the 14 C in a given sample to decay, so scientists say that its half-life is years.
When an organism is alive and acquiring carbon, its 14 C content reaches an equilibrium with its environment. Thus, by measuring how much 14 C is left in a dead plant or animal, and then checking this against the background 14 C level in the atmosphere, scientists can discern how long ago that organism died.
Radiocarbon dating is an effective way to date carbon-based artifacts e. Once archaeologists know the age of an organic sample, they can Types dating methods apply that date to other archaeological remains found in the same stratigraphic layer. Charcoal was a relatively common find on the excavations I worked on. Photo downloaded from Needpix. Modern radiocarbon techniques can produce accurate with small sample sizes, but radiocarbon dating still has drawbacks.
The main issue is contamination. If an archaeological sample comes into contact with another carbon-based object, it can alter the amount of 14 C in that sample, making any subsequent radiocarbon dates inaccurate. Related to contamination is the reservoir Types dating methods. Consequently, radiocarbon dates obtained from marine samples any organism that lived in the sea frequently appear older than the object actually is.
This is a serious problem in regions like the Arcticwhere indigenous peoples have long relied on Types dating methods mammals — including seals — to survive.
Archaeological sites in the Arctic can be so inundated with seal oil that it becomes difficult to generate accurate radiocarbon dates, because many of the samples suffer from the marine reservoir effect. Furthermore, radiocarbon dates must be calibrated.
This information, along with a powerful absolute dating method in its own right, comes from tree rings. We will continue discussing archaeological dating methods here on StoneAgeMan with dendrochronology, or tree ring dating.
Relative Dating Methods There are two overarching classes of dating methods: relative and absolute. Stratigraphy When excavating an archaeological site, you can literally see the layers of dirt and debris that have accumulated over time. Josh Gross Josh Gross is a writer with education and experience in a wide range of fields, including multiple branches of social and ecological sciences. He is also an avocational archaeologist, having worked on excavations in Belize and Ohio. Josh is currently a volunteer in the Cleveland Museum of Natural History's archaeology lab, and a member of a Northern Ohio-based archaeological society called Firelands Archaeology.
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