Dating Fossils and Archaeological Evidence
What is Archaeology?
Archaeology is the study of human history, prehistory and culture through the excavation of sites to find fossilised remains. Archaeology also involves the analysis of artefacts, inscriptions or monuments.
The fossil record is the sum of all the fossilised artefacts and their location within the Earth's rock strata. The fossil record provides information about the history of life on Earth, for example, how organisms used to look like, where they lived and how they evolved.
Transitional fossils are fossils of organisms that depict the intermediate form during evolution, between the ancestral form and the new form. Transitional fossils are a part of the fossil record and identify the change that has occurred over time.
The fossil record is the sum of all the fossilised artefacts and their location within the Earth's rock strata. The fossil record provides information about the history of life on Earth, for example, how organisms used to look like, where they lived and how they evolved.
Transitional fossils are fossils of organisms that depict the intermediate form during evolution, between the ancestral form and the new form. Transitional fossils are a part of the fossil record and identify the change that has occurred over time.
Relative Dating Techniques
To determine the comparative age of a fossil, stratigraphy can be used. The principle of superposition states that the bottom layers of rock strata are older than the top layers of rock strata. Thus, the level of rock strata in which a fossil was find can identify the relative age of that fossil.
In addition, the principle of correlation using index fossils can be used to identify the age of a fossil. Index fossils are fossils of a short-lived species that were geographically wide-spread and easy to find in rock strata, therefore it can be used to correlate the age of fossils that were found in the same layer of rock strata in which the index fossil was found. Relative dating techniques only provide an estimate of the age of a fossil and is therefore not 100% accurate. Thus, relative dating can be used as an estimate to identify the age of hominin artefacts, fossils or tools. |
Absolute Dating Techniques
Radioisotopic dating techniques can be used to determine the absolute age of a fossil by comparing the percentage of a radioactive isotope to the percentage of that isotope found in the atmosphere. Since different radioisotopes have different half lives, different isotopes must be used to date different types of fossils.
Carbon-14 dating is used to date fossils that are 50,000 years old or younger since carbon-14 has a half life of 5,730 years. A living organism has equal proportions of carbon-12 and carbon-14 within their body since they are taking in both carbon-12 and carbon-14 from their environment. When an organism dies, the amount of carbon-14 in their body starts to decline since it is an unstable isotope and it will begin to decay. Therefore, carbon-14 dating can only be used on archaeological evidence from either Homo neanderthalensis or Homo sapiens. Long range dating involves finding the percentage of radioisotopes, such as potassium-40 to argon-4o or uranium-238 to lead-207, in the rocks surrounding a fossil. Potassium-40 has a half life of 1,300 million years, whereas uranium-238 has a half life of 704 million years. Long range dating can therefore be used on archaeological evidence from some of the very ape-like hominins, such as Ardipithecus ramidus, all the way to Homo heidelbergensis. Electron spin resonance is a technique used to date organic samples aged between 50,000 to 500,000 years old. When an object is buried, natural radiation from the soil bombards the object and causes electrons to move and become trapped in a higher energy state. This technique is referred to as the 'electron clock' since the number of high energy electrons is used to determine when the sample was buried. Electron spin resonance can be used to identify the exact age of archaeological evidence from Homo heidelbergensis, Homo floresiensis, Homo neanderthalensis and some evidence from Homo sapiens. |
Paleomagnetic dating is a technique used to date a fossil by comparing the direction that the magnetic particles are orientated within a layer of sediment to the known worldwide shifts in Earth's magnetic field over geologic time. This method is often used to date archaeological evidence that is aged between 1 to 3 million years old.
The molecular clock is a dating method that compares the amount of genetic variation between living organisms to the average rate of genetic mutation over time. Genetic material, such as DNA, decays readily. Therefore, the molecular clock can only be used to determine how long ago two different living species shared a common ancestor, by comparing the amount of genetic variations in their DNA.
The molecular clock is a dating method that compares the amount of genetic variation between living organisms to the average rate of genetic mutation over time. Genetic material, such as DNA, decays readily. Therefore, the molecular clock can only be used to determine how long ago two different living species shared a common ancestor, by comparing the amount of genetic variations in their DNA.
Issues arising with Archaeology
The fossil record provides evidence for australopithecines (hominins that are very ape-like) and evidence for Homos (hominins that are human-like). However, there has been no discovery of transitional fossils between these 2 genera. Therefore, only assumptions can be made about the transition of hominins from Australopithecus to Homo based on Charles Darwin's theories. However, a lot of archaeological evidence suggests that new fossil forms evolved without any apparent ancestral forms. The lack of transitional fossils led many scientists to develop the theory that the evolution of the Homo genus was like a big bang. This contradicts Darwin's understanding of evolution, since he theorised that evolution was the result of small variations that gradually accumulated. In addition, the lack of transitional fossils in the fossil record also contradicts Darwin's idea that all animals are related through common ancestry (Luskin, 2015).
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