# Dating Fossils – How Are Fossils Dated?

For rocks dating back to the beginning of the solar system, this requires extremely long-lived parent isotopes, making measurement of such rocks' exact ages imprecise. And the wisdom takes you away from the faith, and satan knows it. This is not at all true, though it is implied by some young-Earth literature. The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state.

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The aging process in human beings is easy to see. Hugh Ross, the founder and head of the ministry, holds a PhD in Astronomy. The rate of creation of carbon appears to be roughly constant, as cross-checks of carbon dating with other dating methods show it gives consistent results. One of these techniques is called the lead-lead technique because it determines the ages from the lead isotopes alone. Several things can on rare occasions cause problems for the rubidium-strontium dating method.

Principles of Radiometric Dating. Relative Dating with Fossils: Index Fossils as Indicators of Time. Methods of Geological Dating: Numerical and Relative Dating. What is Relative Dating? Absolute Time in Geology. What is Carbon Dating? Applications of Nuclear Chemistry. Major Eons, Eras, Periods and Epochs. What is Relative Age? Prentice Hall Earth Science: Remedial High School Physical Science. Holt McDougal Earth Science: Middle School Life Science: Radiometric dating is used to estimate the age of rocks and other objects based on the fixed decay rate of radioactive isotopes.

Radiometric Dating The aging process in human beings is easy to see. Radioactive Decay The methods work because radioactive elements are unstable, and they are always trying to move to a more stable state.

Half-Life So, what exactly is this thing called a half-life? Uranium-Lead Dating There are different methods of radiometric dating that will vary due to the type of material that is being dated. Potassium-Argon and Rubidium-Strontium Dating 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. Radiocarbon Dating 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?

Want to learn more? Select a subject to preview related courses: Lesson Summary Let's review. Learning Outcomes As a result of watching this video, you might be able to: Compare radiometric dating, radioactive decay and half-life Understand that uranium-lead dating is one of the most reliable radiometric dating methods Relate the processes of potassium-argon and rubidium-strontium dating Determine how radiocarbon dating works and recognize why it is important.

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What grade level do you primarily teach? Grade level is required. What subject do you primarily teach? Its wood was dated using 14 C to be about 4, years old. Other methods of dating are used for non-living things.

A potassium-argon method of dating, developed in , measures the amount of 40 Ar arising from the 40 K decay and is compared to the amount of 40 K remaining in the rock. From the ratio, the time since the formation of the rock can be calculated. The age of our galaxy and earth also can be estimated using radioactive dating. Using the decays of uranium and thorium, our galaxy has been found to be between 10 and 20 billion years old and the earth has been found to be 4. The Universe must be older than our galaxy.

Within experimental error, this estimate agrees with the 15 billion year estimate of the age of the Universe. The technique of comparing the abundance ratio of a radioactive isotope to a reference isotope to determine the age of a material is called radioactive dating. Some nuclides are inherently unstable. That is, at some point in time, an atom of such a nuclide will undergo radioactive decay and spontaneously transform into a different nuclide.

This transformation may be accomplished in a number of different ways, including alpha decay emission of alpha particles and beta decay electron emission, positron emission, or electron capture. Another possibility is spontaneous fission into two or more nuclides. While the moment in time at which a particular nucleus decays is unpredictable, a collection of atoms of a radioactive nuclide decays exponentially at a rate described by a parameter known as the half-life , usually given in units of years when discussing dating techniques.

After one half-life has elapsed, one half of the atoms of the nuclide in question will have decayed into a "daughter" nuclide or decay product. In many cases, the daughter nuclide itself is radioactive, resulting in a decay chain , eventually ending with the formation of a stable nonradioactive daughter nuclide; each step in such a chain is characterized by a distinct half-life. In these cases, usually the half-life of interest in radiometric dating is the longest one in the chain, which is the rate-limiting factor in the ultimate transformation of the radioactive nuclide into its stable daughter.

Isotopic systems that have been exploited for radiometric dating have half-lives ranging from only about 10 years e. For most radioactive nuclides, the half-life depends solely on nuclear properties and is essentially a constant.

It is not affected by external factors such as temperature , pressure , chemical environment, or presence of a magnetic or electric field. For all other nuclides, the proportion of the original nuclide to its decay products changes in a predictable way as the original nuclide decays over time.

This predictability allows the relative abundances of related nuclides to be used as a clock to measure the time from the incorporation of the original nuclides into a material to the present.

The basic equation of radiometric dating requires that neither the parent nuclide nor the daughter product can enter or leave the material after its formation. The possible confounding effects of contamination of parent and daughter isotopes have to be considered, as do the effects of any loss or gain of such isotopes since the sample was created.

It is therefore essential to have as much information as possible about the material being dated and to check for possible signs of alteration. Alternatively, if several different minerals can be dated from the same sample and are assumed to be formed by the same event and were in equilibrium with the reservoir when they formed, they should form an isochron.

This can reduce the problem of contamination. In uranium—lead dating , the concordia diagram is used which also decreases the problem of nuclide loss. Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample. For example, the age of the Amitsoq gneisses from western Greenland was determined to be 3. Accurate radiometric dating generally requires that the parent has a long enough half-life that it will be present in significant amounts at the time of measurement except as described below under "Dating with short-lived extinct radionuclides" , the half-life of the parent is accurately known, and enough of the daughter product is produced to be accurately measured and distinguished from the initial amount of the daughter present in the material.

The procedures used to isolate and analyze the parent and daughter nuclides must be precise and accurate. This normally involves isotope-ratio mass spectrometry. The precision of a dating method depends in part on the half-life of the radioactive isotope involved. For instance, carbon has a half-life of 5, years.

After an organism has been dead for 60, years, so little carbon is left that accurate dating can not be established. On the other hand, the concentration of carbon falls off so steeply that the age of relatively young remains can be determined precisely to within a few decades. If a material that selectively rejects the daughter nuclide is heated, any daughter nuclides that have been accumulated over time will be lost through diffusion , setting the isotopic "clock" to zero.

The temperature at which this happens is known as the closure temperature or blocking temperature and is specific to a particular material and isotopic system. These temperatures are experimentally determined in the lab by artificially resetting sample minerals using a high-temperature furnace.

As the mineral cools, the crystal structure begins to form and diffusion of isotopes is less easy. At a certain temperature, the crystal structure has formed sufficiently to prevent diffusion of isotopes.

This temperature is what is known as closure temperature and represents the temperature below which the mineral is a closed system to isotopes. Thus an igneous or metamorphic rock or melt, which is slowly cooling, does not begin to exhibit measurable radioactive decay until it cools below the closure temperature.

The age that can be calculated by radiometric dating is thus the time at which the rock or mineral cooled to closure temperature. This field is known as thermochronology or thermochronometry. The mathematical expression that relates radioactive decay to geologic time is [12] [15].

The equation is most conveniently expressed in terms of the measured quantity N t rather than the constant initial value N o. The above equation makes use of information on the composition of parent and daughter isotopes at the time the material being tested cooled below its closure temperature.

This is well-established for most isotopic systems. Plotting an isochron is used to solve the age equation graphically and calculate the age of the sample and the original composition. Radiometric dating has been carried out since when it was invented by Ernest Rutherford as a method by which one might determine the age of the Earth. In the century since then the techniques have been greatly improved and expanded.

The mass spectrometer was invented in the s and began to be used in radiometric dating in the s. It operates by generating a beam of ionized atoms from the sample under test. The ions then travel through a magnetic field, which diverts them into different sampling sensors, known as " Faraday cups ", depending on their mass and level of ionization. On impact in the cups, the ions set up a very weak current that can be measured to determine the rate of impacts and the relative concentrations of different atoms in the beams.

Uranium—lead radiometric dating involves using uranium or uranium to date a substance's absolute age. This scheme has been refined to the point that the error margin in dates of rocks can be as low as less than two million years in two-and-a-half billion years. Uranium—lead dating is often performed on the mineral zircon ZrSiO 4 , though it can be used on other materials, such as baddeleyite , as well as monazite see: Zircon has a very high closure temperature, is resistant to mechanical weathering and is very chemically inert.

Zircon also forms multiple crystal layers during metamorphic events, which each may record an isotopic age of the event. One of its great advantages is that any sample provides two clocks, one based on uranium's decay to lead with a half-life of about million years, and one based on uranium's decay to lead with a half-life of about 4. This can be seen in the concordia diagram, where the samples plot along an errorchron straight line which intersects the concordia curve at the age of the sample.

### Iamges: types of radioactive dating techniques

The electron-capture decay mentioned above does not take place in cosmic rays until they slow down. On the other hand, the existence in nature of parent isotopes with half lives around a billion years and longer is strong evidence that the Earth was created not longer ago than several billion years.

As an example of incorrect application of these conditions to dating, one young-Earth proponent suggested that God used plasma conditions when He created the Earth a few thousand years ago. These have been dated at up to about four billion years. The fact that dating techniques most often agree with each other is why scientists tend to trust them in the first place.

Carbon in particular is used to date material such as bones, wood, cloth, paper, and other techniiques tissue from either plants or animals. The decay rates might be **types of radioactive dating techniques** down over time, leading to incorrect old dates. This book talks about the misuse of science by both hard-line atheists and by young-Earth creationists. The important point to note is that, techniquess than giving wrong age *types of radioactive dating techniques,* this datign simply does not give a date if the system has been disturbed. While uranium is water-soluble, thorium and protactinium are not, and so they are selectively precipitated into ocean-floor sedimentsfrom which their ratios are measured. A stronger magnetic field shields the upper atmosphere better from charged cosmic rays, resulting in less carbon production now than in the past. Nuclear chemists and geologists use a different kind of figure to show all of the isotopes.