Geologic Age Dating Explained - Kids Discover
The relative age is the age relative to surrounding fossils; it is not an exact age. Absolute aging, which is also known as absolute dating, uses. Relative dating to determine the age of rocks and fossils . absolute dating methods provide chronological estimates of the age of certain geological materials. Geologists often need to know the age of material that they find. Most absolute dates for rocks are obtained with radiometric methods.
Dating Fossils – How Are Fossils Dated? - thedom.info
But the most accurate forms of absolute age dating are radiometric methods. 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.
Dating Fossils – How Are Fossils Dated?
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.How Does Radiocarbon Dating Work? - Instant Egghead #28
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?
Geologic Age Dating Explained
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?
There are two main methods determining a fossils age, relative dating and absolute dating. Relative dating is used to determine a fossils approximate age by comparing it to similar rocks and fossils of known ages.
Absolute dating is used to determine a precise age of a fossil by using radiometric dating to measure the decay of isotopes, either within the fossil or more often the rocks associated with it. Relative Dating The majority of the time fossils are dated using relative dating techniques. Using relative dating the fossil is compared to something for which an age is already known.
For example if you have a fossil trilobite and it was found in the Wheeler Formation. The Wheeler Formation has been previously dated to approximately million year old, so we know the trilobite is also about million years old. Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.
Index fossils are fossils that are known to only occur within a very specific age range. Typically commonly occurring fossils that had a widespread geographic distribution such as brachiopods, trilobites, and ammonites work best as index fossils.
DETERMINING AGE OF ROCKS AND FOSSILS
If the fossil you are trying to date occurs alongside one of these index fossils, then the fossil you are dating must fall into the age range of the index fossil. Sometimes multiple index fossils can be used. In a hypothetical example, a rock formation contains fossils of a type of brachiopod known to occur between and million years. The same rock formation also contains a type of trilobite that was known to live to million years ago.
Since the rock formation contains both types of fossils the ago of the rock formation must be in the overlapping date range of to million years. Studying the layers of rock or strata can also be useful. Layers of rock are deposited sequentially.