Seventh grade Lesson Relative Age of Rocks | BetterLesson
Plan your minute lesson in Science or Geologic Time with helpful tips from Students will be able to infer the relative age of rocks and fossils from index. This packet on determining age of rocks activities by the students, plus one hour Relative and Absolute Age Dating. Activity: Relative Age of Rocks. 2. There are two basic approaches: relative geologic age dating, and To determine the relative age of different rocks, geologists start with the.
Geologic Age Dating Explained
Strata make the beautiful lines on the rock How Strata are Formed Strata can be long horizontal sections or thin layers. They range from only a few millimeters to many meters thick.
Pressure, heat, and chemical reactions change the sediment into rocks. This process is crucial to the rock cycle. Strata contain many types and patterns. Clay switches off with sandstone layers and carbonate switches off with shales.
These layers create the combinations in the rocks you see below. Watch the video to see how these rock layers are created. The layers on top of the stack are younger.
Stratigraphy - Geology for Kids
This is because the new material usually settles on top of the old material to create new rock. Although superposition does not tell you the exact age, you can learn the age of the rock compared to the other rocks around it.
We call this process of finding out the age of strata based on the rocks around it, relative dating. For example, we know that chalk was formed in the Upper Cretaceous period. So if we find chalk in the strata, we can guess when it was laid down.
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.
- Relative Age of Rocks
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?
Geologic Age Dating Explained - Kids Discover
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.