| CK Foundation
Jul 16, This led him to the ideas that are discussed below. In the process of relative dating, scientists do not determine the exact age of a fossil or. ______ A child ran through the mud puddle. 5. Relative dating is an Earth science term that describes the set of principles and techniques used to sequence geologic events and determine the relative age of rock formations. Below are. Sep 30, There are two basic approaches: relative geologic age dating, and absolute To determine the relative age of different rocks, geologists start with the Like the other kind of dating, geologic dating isn't always simple. Activity.
Where does that rock come from, and what can you learn about it? Stratigraphy is the study is of rock layers, which we call strata. It also is the study of the process that leads to the creation of these layers stratification.
It usually focuses on volcanic rocks and sedimentary rocksor rocks formed by different minerals. 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. This first time of shaking represents one half life, and all those pieces of candy that have the printed M facing up represent a change to the daughter isotope.
Geologic Age Dating Explained
Then, count the number of pieces of candy left with the M facing down. These are the parent isotope that did not change during the first half life. The teacher should have each team report how many pieces of parent isotope remain, and the first row of the decay table Figure 2 should be filled in and the average number calculated. The same procedure of shaking, counting the "survivors", and filling in the next row on the decay table should be done seven or eight more times.
Relative Age of Rocks
Each time represents a half life. Each team should plot on a graph Figure 3 the number of pieces of candy remaining after each of their "shakes" and connect each successive point on the graph with a light line. AND, on the same graph, each group should plot points where, after each "shake" the starting number is divided by exactly two and connect these points by a differently colored line.
After the graphs are plotted, the teacher should guide the class into thinking about: Is it the single group's results, or is it the line based on the class average? U is found in most igneous rocks. Unless the rock is heated to a very high temperature, both the U and its daughter Pb remain in the rock.
A geologist can compare the proportion of U atoms to Pb produced from it and determine the age of the rock. The next part of this exercise shows how this is done. Each team is given a piece of paper marked TIME, on which is written either 2, 4, 6, 8, or 10 minutes. The team should place each marked piece so that "U" is showing.
This represents Uranium, which emits a series of particles from the nucleus as it decays to Lead Pb- When each team is ready with the pieces all showing "U", a timed two-minute interval should start. During that time each team turns over half of the U pieces so that they now show Pb This represents one "half-life" of U, which is the time for half the nuclei to change from the parent U to the daughter Pb A new two-minute interval begins. Continue through a total of 4 to 5 timed intervals.
That is, each team should stop according to their TIME paper at the end of the first timed interval 2 minutesor at the end of the second timed interval 4 minutesand so on. After all the timed intervals have occurred, teams should exchange places with one another as instructed by the teacher.
The task now for each team is to determine how many timed intervals that is, how many half-lives the set of pieces they are looking at has experienced. The half life of U is million years. 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.
DETERMINING AGE OF ROCKS AND FOSSILS
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.