Absolute dating is the process of determining an age on a specified chronology in archaeology and geology. Some scientists prefer the terms chronometric or calendar dating , as use of the word "absolute" implies an unwarranted certainty of accuracy. In archaeology, absolute dating is usually based on the physical, chemical, and life properties of the materials of artifacts, buildings, or other items that have been modified by humans and by historical associations with materials with known dates coins and written history. Techniques include tree rings in timbers, radiocarbon dating of wood or bones, and trapped-charge dating methods such as thermoluminescence dating of glazed ceramics. In historical geology , the primary methods of absolute dating involve using the radioactive decay of elements trapped in rocks or minerals, including isotope systems from very young radiocarbon dating with 14 C to systems such as uranium—lead dating that allow acquisition of absolute ages for some of the oldest rocks on Earth. Radiometric dating is based on the known and constant rate of decay of radioactive isotopes into their radiogenic daughter isotopes.
Relative dating — Science Learning Hub
Comparison of commonly used dating techniques. Radiation, which is a byproduct of radioactive decay, causes electrons to dislodge from their normal position in atoms and become trapped in rocks in the crystal structure of the material. Dating methods like thermoluminescence , sedimentary stimulating luminescence and electron spin resonance , measure the accumulation of electrons in these imperfections, or "traps," in the crystal structure of the material. If the amount of radiation to which an object is determined remains constant, the amount of electrons trapped in the imperfections in the crystal structure of the material will be proportional to the age of the material. These techniques are relative to rocks that are up to about , years relative. However, once rocks or fossils become much older than that, all of the "methods" in the crystal structures become full and no relative electrons can accumulate, even if they are dislodged. The Earth is like a gigantic magnet.
Chronological dating , or simply dating , is the process of attributing to an object or event a date in the past, allowing such object or event to be located in a previously established chronology. This usually requires what is commonly known as a "dating method". Several dating methods exist, depending on different criteria and techniques, and some very well known examples of disciplines using such techniques are, for example, history , archaeology , geology , paleontology , astronomy and even forensic science , since in the latter it is sometimes necessary to investigate the moment in the past during which the death of a cadaver occurred. Dating methods are most commonly classified following two criteria: relative dating and absolute dating.
Geologists often need to know the age of material that they find. They use absolute dating methods, sometimes called numerical dating, to give rocks an actual date, or date range, in number of years. This is different to relative dating, which only puts geological events in time order.