### Quiz & Worksheet - Radiometric Dating & Index Fossils | thebluetones.info

The majority of the lesson focuses on radiometric dating, including an activity where students date their own "rocks and fossils". The attached worksheet helps the students work through the activity, and assesses their ability to analyze a ratio of "elements" and be able to calculate Updated: 02/05/ Utilize this quiz and worksheet to check your understanding of radiometric dating and index fossils. These quiz questions are useful for reviewing. Fossil. Geologists. Half-life. Relative age dating. HELPFUL TERMS activities by the students, plus one hour of discussion To use radiometric dating and the.

### DETERMINING AGE OF ROCKS AND FOSSILS

If you can think of a way to separate the concept of radioactive decay from the terminology to begin with, you may see better results. Once you get through the concepts of radiometric dating, there are a few practice problems in the powerpoint you should go through as a class.

These will help the students with their activity. The activity is simple. Each pair of students should receive a baggie with a ratio of two different things our class used red and white beans, so students got bags full of, say, 38 white beans and 53 red beans. The baggies should be labeled with "what they are sampling".

You can be creative with what they are sampling, but this label helps with misconceptions, such as that fossil fish have their own half lives, and not the carbon in them. 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.

## Absolute dating (radiometric dating)

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. Both the team that turned over a set of pieces and the second team that examined the set should determine how many million years are represented by the proportion of U and Pb present, compare notes, and haggle about any differences that they got. Right, each team must determine the number of millions of years represented by the set that they themselves turned over, PLUS the number of millions of years represented by the set that another team turned over.

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- Use of Index Fossils

Pb atoms in the pegmatite is 1: Using the same reasoning about proportions as in Part 2b above, students can determine how old the pegmatite and the granite are. They should write the ages of the pegmatite and granite beside the names of the rocks in the list below the block diagram Figure 1. This makes the curve more useful, because it is easier to plot it more accurately.

That is especially helpful for ratios of parent isotope to daughter isotope that represent less than one half life. For the block diagram Figure 1if a geochemical laboratory determines that the volcanic ash that is in the siltstone has a ratio of U If the ratio in the basalt is 7: Students should write the age of the volcanic ash beside the shale, siltstone and basalt on the list below the block diagram.

## Radiometric Dating with Index Fossils

Why can't you say exactly what the age of the rock is? Why can you be more precise about the age of this rock than you could about the ages of the rock that has the trilobites and the rock that contains acritarchs and bacteria? Based on cross-cutting relationships, it was established that the pegmatite is younger than the slate and that the slate is younger than the granite.

**How Carbon Dating Works**

Therefore, the slate that contains the acritarch and bacteria is between million years and million years old, because the pegmatite is million years old and the granite is million years old. The slate itself cannot be radiometrically dated, so can only be bracketed between the ages of the granite and the pegmatite. The trilobite-bearing limestone overlies the quartz sandstone, which cross-cuts the pegmatite, and the basalt cuts through the limestone.

Therefore the trilobites and the rock that contains them must be younger than million years the age of the pegmatite and older than million years the age of the basalt. The limestone itself cannot be radiometrically dated, so can only be bracketed between the ages of the granite and the pegmatite.

Some of those elements are stable, and some are radioactive unstable. Radioactive elements are ones that, after a while, will spontaneously break down and turn into other, more stable elements. The nice thing is that this happens in a predictable pattern. The amount that decays into other elements can be predicted; the more years pass, the more will be broken down. By looking at how much of each element there is in a rock, we can trace it back and figure out how old those layers of rock are.

Using this method, we've been able to figure out how old various rocks are and learn a lot about Earth's history. Using these methods, we've even been able to figure out the age of the Earth itself: Use of Index Fossils A related method we use to date rock is the use of reference fossils. Reference fossils are remains of long-dead animals and plants that lived at a known time in history.