Both absolute and relative dating both give answers for how old something is, they do so in different ways and produce different results. An example of the comparison between relative dating and absolute age dating is saying that a daughter is younger than her mom (relative age dating), and saying that a daughter is 16 and her mom is 40 (absolute age dating). Let us learn more about the two.
Relative Dating
Relative dating is a method used by geologists, archaeologists, and paleontologists to determine the relative order or sequence of events in Earth’s history or the history of an archaeological site. Unlike absolute dating, which provides specific numerical ages, relative dating does not yield exact ages but helps establish the chronological relationships between events or objects.
In other words, Relative dating does not offer specific dates, it simply allows to determine if one artifact, fossil, or stratigraphic layer is older than another.
Relative Dating Methods
Stratigraphy: Assuming that soil layers in a deposit accumulate on top of one another, and that the bottom layers will be older than the top layers, stratigraphy allows archaeologists to construct a relative chronological sequence from the oldest (bottom) to youngest (top) layers. Artifacts found in these layers are at least as old as the deposit in which they were found.
Seriation: a technique that was common in the mid-20th century, seriation looks at changes in certain styles of artifacts present at a site. A chronology is developed based on the assumption that one cultural style (or typology) will slowly replace an earlier style over time.
Fluorine dating: a technique that analyzes how much of the chemical fluorine has been absorbed by bones from the surrounding soils in order to determine how long the specimen has been underground.
Absolute Dating
Absolute dating, also known as chronometric dating or radiometric dating, is a method used by scientists to determine the specific age of an object or event in years. Unlike relative dating, which places objects or events in a sequence without specifying their age in years, absolute dating provides a precise numerical age. Absolute dating methods provide more specific origin dates and time ranges, such as an age range in years. How specific these dates can be will depend on what method is used.
Absolute Dating Methods
Radiocarbon Dating: One of the most widely known radiometric dating techniques, radiocarbon dating measures the decay of the radioactive isotope Carbon-14 (C-14) in any organic material found in archaeological deposits, such as wood, plants, textiles, and human or animal remains to determine its age.
Dendrochronology: Since most trees produce a ring of new wood annually, archaeologists use the variations in cross-sections of wood to produce timelines.
Thermoluminescence: Useful for determining the age of pottery or ceramics, it can be used to date materials containing crystalline minerals to a specific heating event in the past (such as when the item was made).
Fission-track dating: A technique that determines age of various minerals and glasses based on the trails of damage done by the spontaneous fission of uranium-238, the most abundant isotope of uranium.
Potassium-argon (K-Ar) and Argon-argon (Ar-Ar): measure the ratio of argon gas in igneous volcanic rock to estimate how much time has elapsed since the rock cooled and solidified.
Archaeomagnetic dating: Magnetic particles in most materials of geological origin, such as rocks and clay, are analyzed to track shifts in the earth’s magnetic fields over time.
Relative vs Absolute Dating: Key Differences
| Points of Comparison | Relative Dating | Absolute Dating |
| Description | Relative dating does not offer specific dates, it simply allows to determine if one artifact, fossil, or stratigraphic layer is older than another. | Absolute dating is a technique used to determine the exact age of the artefact or a site using methods such as carbon dating. |
| Techniques | In relative dating techniques like stratigraphy, cross dating and biostratigraphy are used to know which of the object is older. | In absolute dating, techniques like radiometric dating, carbon dating, amino acid dating and trapped electron are used. |
| Use | Relative dating can only be used for igneous and metamorphic rocks if their upper and lower bounding units have fossils, and their age is known in geologic time scale. | Absolute age determination can date igneous and metamorphic rocks. |
| Nature | Relative age is a qualitative measurement. | Absolute age is a quantitative measurement. |
| Precision | Relative dating has a low precision. | Absolute dating has a high precision. |
| Significance | Relative dating arranges the fossils in an order. | Absolute dating determines the numerical age. |
| Implication | Relative dating is cost effective and takes less time. | Absolute dating is expensive and takes time. |
Key Takeaways
- Relative dating does not offer specific dates, it simply allows to determine if one artifact, fossil, or stratigraphic layer is older than another. Absolute dating methods provide more specific origin dates and time ranges, such as an age range in years.
- In both absolute and relative age determination, the vertical order of rock units is essential and follows laws of superposition. This rule states that the bottom rock units are older than the top rock units. Radioactive elements found in the top rock units are younger than the elements in the bottom units. Therefore, fossils in the upper units are younger than the ones at the bottom.
- Both absolute and relative age determination methods help understand the order of formations contributing the law of superposition.
- Absolute age is found by using radioactive minerals in the rock. In the same rock, if there are certain fossils present, then the age of the fossils is assumed to be the same with the determined absolute age coming from radioactive minerals. However, in relative age determination, the only method available involves using these fossils to assume the age as well as the stratigraphy and law of superposition.
- Relative time (chronostratic time) is the subdivisions of Earth geology represented by rocks, fossil records, and order of geological events. These subdivisions in Earth geology and time are globally recognized and accepted by introducing integrated geologic time scale. The events in Earth history are ordered from bottom (older events) to top (younger events) in the geologic time scale which has relative geologic time names. These names are grouped by units in descending order: eons, eras, periods, epochs, and ages.