Radiocarbon dating Facts for Kids
Radiometric dating is a technique used to date materials based on a . In other radiometric dating methods, the heavy parent isotopes were. It is a type of radiometric dating. The method uses the radioactive isotope carbon- Most organic matter contains carbon. Carbon has different isotopes, which. There are a variety of different ways to figure out how old an object is. But even radiometric dating does not actually directly measure the age.
The isotope used in uranium-thorium dating has a longer half-life, but other factors make it more accurate than radiocarbon dating. The mass spectrometer was invented in the s and began to be used in radiometric dating in the s. The mass spectrometer 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. The uranium -lead radiometric dating scheme is one of the oldest available, as well as one of the most highly respected. It has been refined to the point that the error in dates of rocks about three billion years old is no more than two million years. Uranium-lead dating is best performed on the mineral " zircon " ZrSiO4though it can be used on other materials.
Zircon incorporates uranium atoms into its crystalline structure as substitutes for zirconiumbut strongly rejects lead. It has a very high blocking temperature, and is very chemically inert. 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.
Two other radiometric techniques are used for long-term dating. Potassium - argon dating involves the beta decay of potassium to argon Potassium has a half-life of 1. Rubidium-strontium dating is based on the beta decay of rubidium to strontiumwith a half-life of 50 billion years. This scheme is used to date old igneous and metamorphic rocksand has also been used to date lunar samples.
Chemistry for Kids: Radioactivity and Radiation
Blocking temperatures are so high that they are not a concern. Rubidium-strontium dating is not as precise as the uranium-lead method, with errors of 30 to 50 million years for a 3-billion-year-old sample.
One of the best-known is the carbon C14 radiometric technique. Carbon is a radioactive isotope of carbon, with a half-life of 5, years very short compared with the above.
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In other radiometric dating methods, the heavy parent isotopes were synthesized in the explosions of massive stars that scattered materials through the Galaxy, to be formed into planets and other stars. The parent isotopes have been decaying since that time, and so any parent isotope with a short half-life should be extinct by now.
Carbon is an exception. It is continuously created through collisions of neutrons generated by cosmic rays with nitrogen in the upper atmosphere.
The carbon ends up as a trace component in atmospheric carbon dioxide CO2. An organism acquires carbon from carbon dioxide during its lifetime. Plants acquire it through respiration and photosynthesisand animals acquire it from consumption of plants and other animals. When the organism dies, the carbon begins to decay, and the proportion of carbon left when the remains of the organism are examined provides an indication of the date of its death. Carbon radiometric dating has a range of about 50, years.Creation v. Evolution: How Carbon Dating Works
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. However, local eruptions of volcanoes or other events that give off large amounts of carbon dioxide can reduce local concentrations of carbon and give inaccurate dates.
Radiocarbon dating facts for kids
The releases of carbon dioxide into the biosphere as a consequence of industrialization have also depressed the proportion of carbon by a few percent; conversely, the amount of carbon was increased by above-ground nuclear bomb tests that were conducted into the early s. Also, an increase in the solar wind or the earth's magnetic field above the current value would depress the amount of carbon created in the atmosphere.
Another relatively short-range dating technique is based on the decay of uranium into thorium, a process with a half-life of 80, years It is accompanied by a sister process, in which uranium decays into protactinium, which has a half-life of 34, years. 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. The scheme has a range of several hundred thousand years.
Archaeologists use tree-ring dating dendrochronology to determine the age of old pieces of wood. Trees grow rings on a yearly basis, with the spacing of rings being wider in good growth years than in bad growth years. These spacings can be used to help pin down the age of old wood samples, and also give some hints to climate change.
The technique is only useful to about 4, years in the past, however, because it requires overlapping tree ring series. Although determining geologic time by measuring the rate of deposition of sediments is not reliable over the large scale, it is still useful for certain scenarios, such as the deposition of layers of sediment on the bottom of a stable lake.
The approach is now known as "varve analysis" the term " varve " means a layer or layers of sediment. Another technique used by archaeologists is to inspect the depth of penetration of water vapor into chipped obsidian volcanic glass artifacts.
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The water vapor creates a "hydration rind" in the obsidian, and so this approach is known as "hydration dating" or "obsidian dating", and is useful for determining dates as far back asyears. This method works because some unstable radioactive isotopes of some elements decay at a known rate into daughter products.
This rate of decay is called a half-life. Half-life simply means the amount of time it takes for half of a remaining particular isotope to decay to a daughter product. Good discussion from the US Geological Survey: There are a couple catches, of course. Not all rocks have radioactive elements. Sedimentary rocks in particular are notoriously radioactive-free zones. So to date those, geologists look for layers like volcanic ash that might be sandwiched between the sedimentary layers, and that tend to have radioactive elements.
You might have noticed that many of the oldest age dates come from a mineral called zircon. Each radioactive isotope works best for particular applications.
The half-life of carbon 14, for example, is 5, years. On the other hand, the half-life of the isotope potassium 40 as it decays to argon is 1. Chart of a few different isotope half lifes: If a rock has been partially melted, or otherwise metamorphosed, that causes complications for radiometric absolute age dating as well. Good overview as relates to the Grand Canyon: Which are the youngest?
I also like this simple exercise, a spin-off from an activity described on the USGS site above. Take students on a neighborhood walk and see what you can observe about age dates around you. For example, which is older, the bricks in a building or the building itself?
Are there repairs or cracks in the sidewalk that came after the sidewalk was built? Have students work alone or in pairs to find an article or paper that uses radiometric age dating. What materials were dated? Which method was used e.