The main difference between relative dating and radiometric dating is that relative dating is the method used to determine the age of rock layers according to their relative depth whereas radiometric dating is the method used to determine the absolute age with the use of decaying products of the natural radioactive isotopes present in the material. Furthermore, in an undeformed sequence of sedimentary rocks, each layer of rock is older than the one above it while electron spin resonance and thermoluminescence are the techniques in radioactive dating.
In brief, relative dating and radiometric dating are two methods of dating fossils. Generally, the study of fossils is important for the determination of the kind of organism it represents, how the organism lived, and how it was preserved on the Earth’s surface over the past 4.6 billion years.
Key Areas Covered
1. What is Relative Dating
– Definition, Method of Dating, Importance
2. What is Radioactive Dating
– Definition, Method of Dating, Importance
3. What are the Similarities Between Relative Dating and Radioactive Dating
– Outline of Common Features
4. What is the Difference Between Relative Dating and Radioactive Dating
– Comparison of Key Differences
Key Terms
Absolute Dating, Fossil Dating, Radioactive Dating, Radioactive Isotopes, Relative Dating, Strata
What is Relative Dating
Relative dating is the method of dating the relative age of geological events preserved in rock records depending on the relative ages of the strata. Here, strata are the many horizontal layers at the surface of the earth. The study of strata by working out the relative ages of rocks is called stratigraphy. Especially, relative dating is important for dating sedimentary and volcanic rocks.
Figure 1: The San Rafael Swell – Sedimentary Rock
Principles
Furthermore, the principle of original horizontality refers to the deposition of the layers of strata in a horizontal or nearly horizontal manner. Also, the principle of superposition depends on the principle of horizontality and states that in an undeformed sequence of sedimentary rocks, each layer of rock is older than the one above it and younger than the one below it. Therefore, in a sequence of rock layers, the oldest ones occur at the bottom while the youngest ones occur at the top.
Figure 2: Layers of a Sedimentary Rock
Besides, the disturbance of rocks in events such as fault movements is described by the principle of cross-cutting relationships. However, the age of fossils is important in revealing the relative ages of rocks preserved in two different areas. Here, the principle of faunal succession is useful and it states that different fossil species always appear and disappear in the same order and that once a fossil species goes extinct, it disappears and cannot reappear in younger rocks.
Moreover, index fossils, which occur in a limited interval of times are the fossil species important in distinguishing one layer of rocks from another. Significantly, the fossils of pigs or rodents are better as index fossils as they as more common and easy to identify.
What is Radioactive Dating
Radioactive dating is another method of determining the age of, especially, rocks and fossils. It determines the absolute age of the geological materials or fossils. Furthermore, radiometric dating depends on the natural radioactive decay of a particular element such as carbon or potassium. Also, the techniques of radioactive dating include electron spin resonance and thermoluminescence, which assess the effects of radioactivity on the accumulation of electrons in traps in the crystal structure of a mineral in to determine the age of the rocks or fossils.
Figure 3: Decay of Carbon 14
Principles
As everyone knows, the atomic nucleus of an element contains protons and neutrons while the electrons occur in orbits around the nucleus. Furthermore, the number of protons in a particular element is constant, but its nucleus may contain a variable number of neutrons, forming isotopes of that element with different atomic masses. As an example, the three isotopes of carbon are carbon 12, carbon 13, and carbon 14 where carbon 14 contains an unstable nucleus, which decays to form its daughter isotope, nitrogen 14, which is stable. Here, the amount of time carbon 14 takes for half of the parent isotope to decay into daughter isotopes is called the half-life of an isotope.
Typically, minerals in rocks contain these radioactive isotopes and hence, the abundance of parent and daughter isotopes of a radioisotope with a known half-life of a sample can be used to determine the age of that particular rock as a numerical value.
Similarities Between Relative Dating and Radioactive Dating
- Relative dating and radioactive dating are two methods in archaeology to determine the age of fossils and rocks.
- The study of fossils is important for the determination of the kind of organism it represents, how the organism lived, and how it was preserved on the Earth’s surface over the past 4.6 billion years.
Difference Between Relative Dating and Radioactive Dating
Definition
Relative dating refers to the science of determining the relative order of past events, without necessarily determining their absolute age. On the other hand, radioactive dating refers to the technique used to date materials such as rocks or carbon, in which trace and radioactive impurities were selectively incorporated during their formation.
Significance
Relative dating determines the relative age of rock layers according to their relative depth. However, radiometric dating determines the absolute age with the use of decaying products of the natural radioactive isotopes.
Principle
In an undeformed sedimentary rock, each bottom layer is older than the one above it. In comparison, radioactive dating assesses the effects of radioactivity on the accumulation of electrons in traps in the crystal structure.
Techniques
Also, relative dating is based on the principle of original horizontality, the principle of superposition, the principle of cross-cutting relationships, and the principle of faunal succession while electron spin resonance and thermoluminescence are the techniques used in radioactive dating.
Type of Materials to be Dated
Relative dating is important to date sedimentary and volcanic rocks while radioactive dating is important for dating fossils and rocks.
Importance
Relative dating determines the age with respect to the age of top and bottom strata in a relative manner. While radioactive dating determines the absolute age as a numerical value.
Conclusion
In brief, relative dating is the method of determining the relative age of a fossil. Generally, it depends on the age of the top and bottom layers of an undeformed sequence of sedimentary rocks. In contrast, radioactive dating is the method of determining the absolute age of a fossil. However, it uses the remnants of radioactive traces. Also, the techniques involved in the process are electron spin resonance or thermoluminescence. Therefore, the main difference between relative dating ad radioactive dating is the principle and type of dating.
References:
1. Peppe, D. J. & Deino, A. L. (2013) Dating Rocks and Fossils Using Geologic Methods. Nature Education Knowledge 4(10):1. Available Here.
Image Courtesy:
1. “Interesting Dirt Color Near Emery, Utah” By Ken Lund (CC BY-SA 2.0) via Flicker
2. “Fossils” By Kurt Rosenkrantz (CC BY-SA 3.0) via Commons Wikimedia
3. “Carbon-Dating-Flashcards” By Zappys Technology Solutions (CC BY 2.0) via Ficker
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