Dating methods in Archaeology. Are they accurate?
Dating refers to the archaeological tool to date artefacts and sites, and to properly construct history.
All methods can be classified into two basic categories:
a) Relative dating methods : Based on a discipline of geology called stratigraphy, rock layers are used to decipher the sequence of historical geological events. Relative techniques can determine the sequence of events but not the precise date of an event, making these methods unreliable.
b) Absolute dating methods: These methods are based on calculating the date of artefacts in a more precise way using different attributes of materials. This method includes carbon dating and thermoluminescence.
The absolute dating method first appeared in 1907 with Lord Rutherford and Professor Boltwood at Yale University, but wasn’t accepted until the 1950s. The first method was based on radioactive elements whose property of decay occurs at a constant rate, known as the half-life of the isotope.
Today, many different radioactive elements have been used, but the most famous absolute dating method is radiocarbon dating, which uses the isotope 14C. This isotope, which can be found in organic materials and can be used only to date organic materials, has been incorrectly used by many to make dating assumptions for non-organic material such as stone buildings. The half-life of 14C is approximately 5730 years, which is too short for this method to be used to date material millions of years old. The isotope of Potassium-40, which has a half-life of 1.25 Billion years, can be used for such long measurements.
Another absolute dating method is thermoluminescence, which dates the last time an item was heated. It is the only method that can be used to date rocks, pottery and minerals for dates that are approximately between 300 to 10,000 years old. This method is based on the fact that when a material is heated or exposed to sunlight, electrons are released and some of them are trapped inside the item. Once you heat this item again using high temperatures, the trapped electrons become excited and recombine with the item’s material. This process frees energy in the form of light, which can be measured. By making multiple measurements (you need at least two for a date estimate) we can find out how much radiation the item was exposed to over the years and can get dating estimates related to when the item was last heated. This method has the following restrictions:
a) It cannot be used to date items many thousands of years old;
b) it can only be used in non-organic materials; and
c) the materials to be dated must have been heated to more than 350 degrees Celsius. This method is usually used with carbon dating.
All of the current dating methods are going through refinement. Archaeologists are seeking an accurate dating technique, but this method is yet to be found.
Here we come to the question of how accurate the dates are that we currently have regarding the history of the human race and our planet. Even though more than one method of verification is used in most cases, the lack of an accurate method to date non-organic materials lends a certain degree of uncertainty to the accepted history of our planet.
It is also important not to forget that throughout the history of humankind any discovery that shakes the status quo is always under attack until it becomes established, and we are in an era where many of the things that we once considered certain will become errors of our past.
By John Black
Dating Techniques in Archaeology - Archaeology Expert
Introduction to Dating methods