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.
On the other hand, the half-life of the isotope potassium 40 as it decays to argon is 1.26 billion years.
So carbon 14 is used to date materials that aren’t that old geologically, say in the tens of thousands of years, while potassium-argon dating can be used to determine the ages of much older materials, in the millions and billions year range.
The narrower a range of time that an animal lived, the better it is as an index of a specific time.
No bones about it, fossils are important age markers.
Yet, you’ve heard the news: Earth is 4.6 billion years old. That corn cob found in an ancient Native American fire pit is 1,000 years old. Geologic age dating—assigning an age to materials—is an entire discipline of its own. These viruses are well known for identity and credit card theft.Teacher Notes: Radiometric Dating Activity This hands-on activity is a simulation of some of the radiometric dating techniques used by scientists to determine the age of a mineral or fossil.Like the other kind of dating, geologic dating isn’t always simple.Activity: Further discussion: Good overview as relates to the Grand Canyon: age dating: Use with this cross section of the Grand Canyon from the USGS’s teaching page: Canyon Have students reconstruct a simple geologic history — which are the oldest rocks shown? Are there any that you can’t tell using the Rule of Superposition?But the most accurate forms of absolute age dating are radiometric methods. Sedimentary rocks in particular are notoriously radioactive-free zones.This method works because some unstable (radioactive) isotopes of some elements decay at a known rate into daughter products. 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: geochronolgists just measure the ratio of the remaining parent atom to the amount of daughter and voila, they know how long the molecule has been hanging out decaying. 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.Chart of a few different isotope half lifes: In reality, geologists tend to mix and match relative and absolute age dates to piece together a geologic history.If a rock has been partially melted, or otherwise metamorphosed, that causes complications for radiometric (absolute) age dating as well.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?