# Absolute dating methods

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## Dating Fossils – How Are Fossils Dated?

As a member, you'll also get unlimited access to over 75, lessons in math, English, science, history, and more. Plus, get practice tests, quizzes, and personalized coaching to help you succeed. Already registered? Log in here for access. Log in or sign up to add this lesson to a Custom Course. Log in or Sign up. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic. The aging process in human beings is easy to see.

As we age, our hair turns gray, our skin wrinkles and our gait slows. However, rocks and other objects in nature do not give off such obvious clues about how long they have been around. So, we rely on radiometric dating to calculate their ages. Radiometric dating, or radioactive dating as it is sometimes called, is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes.

Different methods of radiometric dating can be used to estimate the age of a variety of natural and even man-made materials. The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state. So, they do this by giving off radiation. This process by which an unstable atomic nucleus loses energy by releasing radiation is called radioactive decay. The thing that makes this decay process so valuable for determining the age of an object is that each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life.

So, if you know the radioactive isotope found in a substance and the isotope's half-life, you can calculate the age of the substance. So, what exactly is this thing called a half-life? Well, a simple explanation is that it is the time required for a quantity to fall to half of its starting value. So, you might say that the 'full-life' of a radioactive isotope ends when it has given off all of its radiation and reaches a point of being non-radioactive.

When the isotope is halfway to that point, it has reached its half-life. There are different methods of radiometric dating that will vary due to the type of material that is being dated. For example, uranium-lead dating can be used to find the age of a uranium-containing mineral. It works because we know the fixed radioactive decay rates of uranium, which decays to lead, and for uranium, which decays to lead So, we start out with two isotopes of uranium that are unstable and radioactive.

They release radiation until they eventually become stable isotopes of lead. These two uranium isotopes decay at different rates. In other words, they have different half-lives. The half-life of the uranium to lead is 4. The uranium to lead decay series is marked by a half-life of million years. These differing rates of decay help make uranium-lead dating one of the most reliable methods of radiometric dating because they provide two different decay clocks.

This provides a built-in cross-check to more accurately determine the age of the sample. Uranium is not the only isotope that can be used to date rocks; we do see additional methods of radiometric dating based on the decay of different isotopes. For example, with potassium-argon dating , we can tell the age of materials that contain potassium because we know that potassium decays into argon with a half-life of 1.

With rubidium-strontium dating , we see that rubidium decays into strontium with a half-life of 50 billion years. By anyone's standards, 50 billion years is a long time. In fact, this form of dating has been used to date the age of rocks brought back to Earth from the moon. So, we see there are a number of different methods for dating rocks and other non-living things, but what if our sample is organic in nature? For example, how do we know that the Iceman, whose frozen body was chipped out of glacial ice in , is 5, years old?

Well, we know this because samples of his bones and hair and even his grass boots and leather belongings were subjected to radiocarbon dating. Radiocarbon dating , also known as carbon dating or simply carbon dating, is a method used to determine the age of organic material by measuring the radioactivity of its carbon content. So, radiocarbon dating can be used to find the age of things that were once alive, like the Iceman.

And this would also include things like trees and plants, which give us paper and cloth. So, radiocarbon dating is also useful for determining the age of relics, such the Dead Sea Scrolls and the Shroud of Turin. With radiocarbon dating, the amount of the radioactive isotope carbon is measured. Compared to some of the other radioactive isotopes we have discussed, carbon's half-life of 5, years is considerably shorter, as it decays into nitrogen Carbon is continually being created in the atmosphere due to the action of cosmic rays on nitrogen in the air.

Carbon combines with oxygen to create carbon dioxide. Because plants use carbon dioxide for photosynthesis, this isotope ends up inside the plant, and because animals eat plants, they get some as well. When a plant or an animal dies, it stops taking in carbon The existing carbon within the organism starts to decay back into nitrogen, and this starts our clock for radiocarbon dating. A scientist can take a sample of an organic material when it is discovered and evaluate the proportion of carbon left in the relic to determine its age.

Let's review. Radiometric dating is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes. The decay rate is referring to radioactive decay , which is the process by which an unstable atomic nucleus loses energy by releasing radiation. Each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life or, in other words, the time required for a quantity to fall to half of its starting value.

There are different methods of radiometric dating. Uranium-lead dating can be used to find the age of a uranium-containing mineral. Uranium decays to lead, and uranium decays to lead The two uranium isotopes decay at different rates, and this helps make uranium-lead dating one of the most reliable methods because it provides a built-in cross-check. Additional methods of radiometric dating, such as potassium-argon dating and rubidium-strontium dating , exist based on the decay of those isotopes.

Radiocarbon dating is a method used to determine the age of organic material by measuring the radioactivity of its carbon content. With radiocarbon dating, we see that carbon decays to nitrogen and has a half-life of 5, years. To unlock this lesson you must be a Study. Create your account. Already a member? Log In. Did you know… We have over college courses that prepare you to earn credit by exam that is accepted by over 1, colleges and universities.

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I am a student I am a teacher. Try Study. What teachers are saying about Study. Coming up next: Conditions of Fossil Preservation: Just checking in. Are you still watching? Keep playing. Your next lesson will play in 10 seconds. Add to Add to Add to. Want to watch this again later? Create an account. What is Radioactive Dating? Principles of Radiometric Dating. Methods of Geological Dating: Numerical and Relative Dating.

Relative Dating with Fossils: Index Fossils as Indicators of Time. What is Relative Dating? What is the Age of the Solar System?

## In other radiometric dating methods, the heavy parent isotopes were produced by nucleosynthesis in supernovas. Geologists often need to know the age of material that they find. They use absolute dating methods, sometimes called numerical dating, to give.

The quest for an absolute chronology in human prehistory: By the early twentieth century there was a growing need within palaeoanthropology and prehistoric archaeology to find a way of dating fossils and artefacts in order to know the age of specific specimens, but more importantly to establish an absolute chronology for human prehistory. The radiocarbon and potassium-argon dating methods revolutionized palaeoanthropology during the last half of the twentieth century. However, prior to the invention of these methods there were attempts to devise chemical means of dating fossil bone.

Despite seeming like a relatively stable place, the Earth's surface has changed dramatically over the past 4. Mountains have been built and eroded, continents and oceans have moved great distances, and the Earth has fluctuated from being extremely cold and almost completely covered with ice to being very warm and ice-free.

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.

## Absolute dating

Radiometric dating , radioactive dating or radioisotope dating is a technique used to date materials such as rocks or carbon , in which trace radioactive impurities were selectively incorporated when they were formed. The method compares the abundance of a naturally occurring radioactive isotope within the material to the abundance of its decay products, which form at a known constant rate of decay. Together with stratigraphic principles , radiometric dating methods are used in geochronology to establish the geologic time scale. By allowing the establishment of geological timescales, it provides a significant source of information about the ages of fossils and the deduced rates of evolutionary change. Radiometric dating is also used to date archaeological materials, including ancient artifacts.

## Radiometric dating

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. Particular isotopes are suitable for different applications due to the types of atoms present in the mineral or other material and its approximate age. For example, techniques based on isotopes with half lives in the thousands of years, such as carbon, cannot be used to date materials that have ages on the order of billions of years, as the detectable amounts of the radioactive atoms and their decayed daughter isotopes will be too small to measure within the uncertainty of the instruments. One of the most widely used and well-known absolute dating techniques is carbon or radiocarbon dating, which is used to date organic remains.

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## Radiometric Dating: Methods, Uses & the Significance of Half-Life

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## Dating Rocks and Fossils Using Geologic Methods

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Absolute dating methods (ANT)