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Given that so few organisms ever become fossilized, any anthropologist or fossil hunter will tell you that finding a fossil is extremely exciting. But this is just the beginning of a fantastic mystery. With the creative application of scientific methods and deductive reasoning, a great deal can be learned about the fossilized organism and the environment in which it lived, leading to enhanced understanding of the world around us.
Context is a crucial concept in paleoanthropology and archaeology. Objects and fossils are interesting in and of themselves, but without context there is only so much we can learn from them. One of the most important contextual pieces is the dating of an object or fossil.
By being able to place it in time, we can compare it more accurately with other contemporary fossils and artifacts or we can better analyze the evolution of a fossil species or artifacts. Dating techniques are divided into two broad : relative dating methods and chronometric sometimes called absolute dating methods.
Relative dating methods are the first used because they rely on simple observational skills. He categorized the artifacts at the museum based on the idea that simpler tools and materials were most likely older than more complex tools and materials. Stone tools must predate metal tools because they do not require special technology to develop. Copper and bronze tools must predate iron because they can be smelted or worked at lower temperatures, etc. You simply know that one artifact or fossil is older than another.
The same is true with fossils that have differences of ages into the hundreds of millions of years. The first relative dating technique is stratigraphy Figure 7. You might have already heard this term if you have watched documentaries on archaeological excavations. It provides a solid foundation for other dating techniques to be used and gives important context to artifacts and fossils found at a site.
Essentially, superposition tells us that things on the bottom are older than things on the top Williams Notice on Figure 7.
It stands to reason that each layer is older than the one immediately on top of it Hester et al. Think of a pile of laundry on the floor. Over the course of a week, as dirty clothes get tossed on that pile, the shirt tossed down on Monday will be at the bottom of the pile while the shirt tossed down on Friday will be at the top. Assuming that the laundry pile was undisturbed throughout the week, if the clothes were picked up layer by layer, the clothing choices that week could be reconstructed in the order that they were worn. This concept may seem simple or even obvious, but it is extremely important in archaeology.
Another important relative dating technique is biostratigraphy. This form of dating looks at the context of a fossil or artifact and compares it to the other fossils and biological remains plant and animal found in the same stratigraphic layers.
For instance, if an artifact is found in the same layer as wooly mammoth remains, you know that it must date to around the last Physical anthropology dating techniques age, when wooly mammoths were still abundant on Earth. In the absence of more specific dating techniques, early archaeologists could prove the great antiquity of stone tools because of their association with extinct animals. The application of this relative dating technique in archaeology was used at the Folsom site in New Mexico. Ever since Europeans encountered people in the Americas, they wondered how long they had been on Physical anthropology dating techniques continent.
Were they recent arrivals from Asia or had their ancestors been there thousands of years? Biostratigraphy helped answer this question before absolute dating techniques had even been invented. Inat a site in Folsom, New Mexico, a stone spear point was discovered embedded in the rib of an extinct species of bison. Because of the undeniable association between the artifact and the ancient animal, there was proof that people had occupied the North American continent since antiquity Cook Similar to biostratigraphic dating is cultural dating Figure 7. This relative dating technique is used to identify the chronological relationships between human-made artifacts.
Cultural dating is based on artifact types and styles Hester et al. For instance, a pocket knife by itself is difficult to date. However, if the same pocket knife is discovered surrounded by cassette tapes and VHS tapes, it is logical to assume that the artifact came from the s or s like the cassette and VHS tapes. The pocket knife could not be dated earlier than the age of the cassette and VHS tapes because the tapes were made no earlier than the s.
In the Thomsen example above, he was able to identify a relative chronology of ancient European tools based on the artifact styles, manufacturing techniques, and raw materials. Cultural dating can be used with any human-made artifacts. Both cultural dating and biostratigraphy are most effective when you are already familiar with the time periods for the artifacts and animals. They are still used today to identify general time periods for sites. Chemical dating was developed in the 19th century and represents one of the early attempts to use soil composition and chemistry to date artifacts.
A specific type of chemical dating is fluorine datingand it is commonly used to compare the age of the soil around artifacts located in close proximity Cook and Ezra-Cohn While this technique is based on chemical dating, it only provides the relative dates of items rather than their absolute ages.
For this reason, fluorine dating is considered a hybrid form of relative and chronometric dating methods discussed below. Soils contain different amounts of chemicals, and those chemicals, such as fluorine, can be absorbed by human and animal bones buried in the soil. The longer the remains are in the soil, the more fluorine they will absorb Cook and Ezra-Cohn Unfortunately, this absorption rate is highly sensitive to temperature, soil pH, and varying fluorine levels in local soil and groundwater Haddy and Hanson This makes it difficult to get an accurate date for the remains or to compare remains between two sites.
However, this technique is particularly useful for determining whether different artifacts come from the same burial context. If they were buried in the same soil for the same length of time, their fluorine atures would match. In addition to bringing worldwide attention to British anthropology, Physical anthropology dating techniques himself became famous for his discovery. As a fossil specimen, Piltdown Man had a large bulbous cranium like modern humans, but a primitive apelike jaw and teeth.
However, as more and more of the human African fossils began emerging, scientists began to suspect Piltdown Man was not the missing link as it had been represented and the credibility of Eoanthropus was brought into scrutiny. They noticed that the teeth had odd wear patterns on them. Dawson had filed them down to better fit the mandible to the maxilla. Fluorine analysis determined that the jaw and cranium had different fluorine atures. Thus, these bones could not have come from the same individual in the same burial environment.
It turned out that the cranium was from two, maybe three, medieval humans and the jaw from a modern Bornean orangutan, Pongo pygmaeus De Groote et al. Furthermore, all of the pieces of the cranium were stained to give a uniform and ancient-looking color. Piltdown Man was a forgery that greatly disrupted legitimate anthropological research and confused the understanding of the fossil record in the early 20th century. Unlike relative dating methods, chronometric dating methods provide specific dates and time ranges.
Many of the chronometric techniques we will discuss are based on work in other disciplines such as chemistry and physics. The Physical anthropology dating techniques developments in studying radioactive materials are extremely accurate and precise in establishing dates for ancient sites and remains. Many of the chronometric dating methods are based on the measurement of radioactive decay of particular elements. Elements are materials that cannot be broken down into more simple materials without losing their chemical identity Brown et al.
Each element consists of an atom that has a specific of protons positively charged particles and electrons negatively charged particles as well as varying s of neutrons particles with no charge. The protons and neutrons are located in the densely compacted nucleus of the atom, but the majority of the volume of an atom is space outside the nucleus around which the electrons orbit see Figure 7. Elements are classified based on the of protons in the nucleus. For example, carbon has six protons, giving it an atomic 6.
Uranium has 92 protons, which means that it has an atomic While the of protons in the atom of an element do not vary, the of neutrons may. Atoms of a given element that have different s of neutrons are known as isotopes. For instance, isotopes of carbon include carbon 12 12 Ccarbon 13 13 Cand carbon 14 14 C. Carbon always has six protons, but 12 C has six neutrons whereas 14 C has eight neutrons.
Because 14 C has more neutrons, it has a greater mass than 12 C Brown et al. Most isotopes in nature are considered stable isotopes and will remain in their normal structure indefinitely.
However, some isotopes are considered unstable isotopes sometimes called radioisotopes because they spontaneously release energy and particles, transforming into stable isotopes Brown et al. The process of transforming the atom by spontaneously releasing energy is called radioactive decay. This change occurs at a predictable rate for nearly all radioisotopes of elements, allowing scientists to use unstable isotopes to measure time passage from a few hundred to a few billion years with a large degree of accuracy and precision.Physical anthropology dating techniques
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