Added: Velvet Mclamb - Date: 24.10.2021 13:32 - Views: 41268 - Clicks: 6650
If you want to know how old someone or something is, you can generally rely on some combination of simply asking questions or Googling to arrive at an accurate answer. This applies to everything from the age of a classmate to the of years the United States has existed as a sovereign nation and counting as of But what about the ages of objects of antiquity, from a newly discovered fossil to the very age of the Earth itself?
Sure, you can scour the Internet and learn rather quickly that the scientific consensus pins the age of of the planet at about 4. But Google didn't invent this ; instead, human ingenuity and applied physics have provided it. Specifically, a process called radiometric dating allows scientists to determine the ages of objects, including the ages of rocks, ranging from thousands of years old to billions of years old to a marvelous degree of accuracy. This relies on a Radiometric dating def combination of basic mathematics and knowledge of the physical properties of different chemical elements.
To understand radiometric dating techniquesyou first have to have an understanding of what is being measured, how the measurement is being made and the theoretical as well as practical limitations of the system of measurement being used. As an analogy, say you find yourself wondering, "How Radiometric dating def or cold is it outside? You need a device to measure this activity a thermometer, of which various kinds exist. You also need to know when you can or cannot apply a particular type of device to the task at hand; for example, if you want to know how hot it is on the inside of an active wood stove, you probably understand that putting a household thermometer intended to measure body temperature inside the stove is not going to prove helpful.
Be aware also that for many centuries, most human "knowledge" of the age of rocks, formations such as the Grand Canyon, and everything else around you was predicated on the Genesis of the Bible, which posits that the entire cosmos is perhaps 10, years old. Modern geological methods have at times proven thorny in the face of such popular but quaint and scientifically unsupported notions.
Radiometric dating takes advantage of the fact that the composition of certain minerals rocks, fossils and other highly durable objects changes over time. Specifically, the relative amounts of their constituent elements shift in a mathematically predictable way thanks to a phenomenon called radioactive decay. This in turn relies on knowledge of isotopessome of which are "radioactive" that is, they spontaneously emit subatomic particles at a known rate.
Isotopes are different versions of the same element e. Some things in nature disappear Radiometric dating def a more or less constant rate, regardless of how much there is to start with and how much remains. For example, certain drugs, including ethyl alcohol, are metabolized by the body at a fixed of grams per hour or whatever units are most convenient.
If someone has the equivalent of five drinks in his system, the body takes five times as long to clear the alcohol as it would if he had one drink in his system. Many substances, however, both biological and chemical, conform to a different mechanism: In a given time period, half of the substance will disappear in a fixed time no matter how much is present to start Radiometric dating def.
Such substances are said to have a half-life. Radioactive isotopes obey this principle, and they have wildly different decay rates. The utility of this lies in being able to calculate with ease how much of a given element was present at the time it was formed based on how much is present at the time of measurement. This is because when radioactive elements first come into being, they are pd to consist entirely of a single isotope. As radioactive decay occurs over time, more and more of this most common isotope "decays" i. Imagine that you enjoy a certain kind of ice cream flavored with chocolate chips.
You have a sneaky, but not especially clever, roommate who doesn't like the ice cream itself, but cannot resist picking out eating the chips — and in an effort to avoid detection, he replaces each one he consumes with a raisin. He is afraid to do this with all of the chocolate chips, so instead, each day, he swipes half of the of remaining chocolate chips and puts raisins in their place, never quite completing his diabolical transformation of your dessert, but getting closer and closer. Say a second friend who is aware of this arrangement visits and notices that your carton of ice cream contains 70 raisins and 10 chocolate chips.
She declares, "I guess you went shopping about three days ago. Because your roommate eats half of the chips on any given day, and not a fixedthe carton must have held 20 chips the day before, 40 the day before that, and 80 the day before that. Calculations involving radioactive isotopes are more formal but follow the same basic principle: If you know the half-life of the radioactive element and can measure how much of each isotope is present, you can figure out the age of the fossil, rock or other entity it comes from.
Elements that have half-lives are said to obey a first-order decay process. They have what is known as a rate constant, usually denoted by k. The relationship between the of atoms present at the start N 0the present at the time of measurement N the elapsed time t, and the rate constant k can be written in two mathematically equivalent ways:.
In addition, you may wish to know the activity A of a sample, typically measured in disintegrations per second or dps. This is expressed simply as:. You don't need to know how these equations are derived, but you should be prepared to use them so solve problems involving radioactive isotopes. Scientists interested in figuring out the age of a fossil or rock analyze a sample to determine the ratio of a given radioactive element's daughter isotope or isotopes to its parent isotope in that sample.
With the element's decay rate, and hence its half-life, Radiometric dating def in advance, calculating its age is straightforward. The trick is knowing which of the various common radioactive isotopes to look for. This in turn depends in the approximate expected age of the object because radioactive elements decay at enormously different rates. Also, not all objects to be dated will have each of the elements commonly Radiometric dating def you can only date items with a given dating technique if they include the needed compound or compounds. Uranium-lead U-Pb dating: Radioactive uranium comes in two forms, uranium and uranium The refers to the of protons plus neutrons.
Uranium's atomic is 92, corresponding to its of protons. The half-life of uranium is 4. Because these differ by a factor of almost Radiometric dating def recall that a billion is 1, times a millionit proves a "check" to make sure you're calculating the age of the rock or fossil properly, making this among the most precise radiometric dating methods. The long half-lives make this dating technique suitable for especially old materials, from about 1 million to 4. U-Pb dating is complex because of the two isotopes in play, but this property is also what makes it so precise. The method is also technically challenging because lead can "leak" out of many types of rocks, sometimes making the calculations difficult or impossible.
U-Pb dating is often used to date igneous volcanic rocks, which can be hard to do because of the lack of fossils; metamorphic rocks; and very old rocks. All of these are hard to Radiometric dating def with the other methods described here. Rubidium-strontium Rb-Sr dating: Radioactive rubidium decays into strontium with a half -life of Not surprisingly, Ru-Sr dating is used to date very old rocks as old as the Earth, in fact, since the Earth is "only" around 4. Strontium exists in other stable i. But because rubidium is abundant in the Earth's crust, the concentration of strontium is much higher than that of the other isotopes of strontium.
Scientists can then compare the ratio of the strontium to the total amount of stable strontium isotopes to calculate the level of decay that produces the detected concentration of strontium This technique is often used to date igneous rocks and very old rocks. Potassium-argon K-Ar dating: The radioactive potassium isotope is K, which decays into both calcium Ca and argon Ar in a ratio of Argon is a noble gas, which means that it is nonreactive and would not be a part of the initial formation of any rocks or fossils.
Any argon found in a rocks or fossils therefore has to be the result of this kind of radioactive decay. The half-life of potassium is 1. Potassium is very abundant in the Earth, making it great for dating because it is found in some levels in most kinds of samples. It is good for dating igneous rocks volcanic rocks. Carbon C dating: Carbon enters organisms from the atmosphere. When the organism dies, no more of the carbon isotope can enter the organism, and it will begin to decay starting at that point.
Carbon decays into nitrogen in the shortest half-life of all the methods 5, yearswhich makes it perfect for dating new or recent fossils. It is mostly only used for organic materials, that is, animal and plant fossils. Carbon cannot be used for samples older than 60, years old. At any given time, the tissues of living organisms all have the same ratio of carbon to carbon When an organism dies, as noted, it stops incorporating new carbon into its tissues, and so the subsequent decay of carbon to nitrogen alters the ratio of carbon to carbon By comparing the ratio of carbon to carbon in dead matter to the ratio when that organism was alive, scientists can estimate the date of the organism's death.
Kevin Beck holds a bachelor's degree in physics with minors in math and chemistry from the University of Vermont. Formerly with ScienceBlogs.
More about Kevin and links to his professional work can be found at www. You are likely to encounter people and other sources that refer to radiometric dating methods generically as "radiocarbon dating " or just "carbon dating. Related Articles Genetic Isolation and Evolution.
Copyright Leaf Group Ltd.Radiometric dating def
email: [email protected] - phone:(340) 327-8416 x 6283