Activities about Sediments

Dr. Passow                                                                               Name_____________________

Activities about Sediments

Introduction

Here are a series of activities that will allow you to learn more about sediments, as well as develop your skills in using a variety of strategies to study our planet. These include:

• using a stereomicroscope to view tiny objects
• finding their actual sizes by comparing them with the scope’s field of view
• separating a sediment sample using a set of sieves and
• representing the grain size distribution using bar graphs

You have used compound microscopes to view prepared slides, plankton, and other objects. Objects viewed with a compound microscope must be both tiny and transparent. A stereomicroscope allows you to look at larger objects, and they may be transparent or opaque, so this instrument is often used to study sediments and soils.

You may conduct these activities in any order. Follow the directions carefully, both those written here and any given orally by your teacher.

In addition, you can earn extra credit on this activity by making a DLESE search. DLESE is the Digital Library for Earth Systems Education, www.dlese.org. It is one of the most valuable search engines available to find almost anything about our planet.

Part 1: Measuring Particle Size under a Stereomicroscope

You can find the diameter of the field of view of a microscope by placing a 1 mm x 1 mm grid across the image and observing how many boxes can be seen. Then use this skill to find the size of sand grains.

Find the diameter of the field of view under 5x and record it here:                mm

            Repeat this activity using the 10x lenses:                mm

            What is the ratio of the fields of view?            to

            What do you predict the field of view would be with 15x lenses?                 mm

            Test your prediction:                mm 

Were you correct? Explain: 

Now place a few sand grains on the grid, choose the best magnification, and try

to find their grain size:                 mm

Explain what you did:

Does your answer match the size range in the chart in the ESRT p. 6?

View the beach sediment samples through your stereomicroscope. Make notes and labeled drawings on a separate sheet that you attach to your report. After you carefully put them back into the container, repeat this with soil samples.

Part 2: Separating and Analyzing Sediment Samples

Beach sands and soils are mixtures composed of mineral fragments and other materials. Geologists and soil scientists often describe them based on their grain size distribution—that is, the percentage of the sample in different diameter ranges.

Samples can be easily separated using a set of sieves—containers that have different size screens inside them. As you do this lab, you will have the chance to practice your skills in using abalance scale, calculating percentages, and showing your results in bar graphs.

Begin by using your balance scale to find the mass of each of the five sieves. Then record them in the table below.

            Next, make sure the sieves are stacked in order (largest screen on top, then next-largest, until smallest screen above pan on bottom.)

Pour a small amount of your sample into the top sieve, cover, and shake for about 10 seconds to make sure all the particles can fall through until they rest on the sieve that is smallest than their diameter.

Find the mass of each sieve and its sample, and record in the table. Then subtract the mass of the empty sieve from the sieve + sample mass to find the mass of each sample, and record these.

                                      Total sample mass:    _____________

            Add all of the sample masses to find the total sample mass and record it on the line at the bottom of the sample mass column.

            Divide each sample mass by the total sample mass to find the percent of the total mass in each sieve, and record these. Round your values to the nearest whole percent (example: 0.437 = 44%.)

            Finally, find the cumulative percent. For sieve 1, this is the same as the sample percent. For sieve 2, it will be the percents in sieves 1 and 2. For sieve 3, it will be the percents in sieves 1, 2, and 3, and so on. The percent in the pan may not be exactly 100 because the percents in each sieve include some rounding.

Part 2: Separating and Analyzing Sediment Samples, cont’d.

            In the table below, record your group’s values and the class’ averages. Then use these to make bar graphs that you attach to your report.

What to Include in Your Lab Report:

• Introduction (What were the reasons you did this activity?)
• Procedure (Tell what you did in each part—1^st person, past tense.)
• Results (Present what you observed in each part, including your bar graphs for the table at the top of this page.)
• Discussion
  • Include one paragraph about soils and one paragraph about beach sediments.
  • Compare the results your group found for the percent and cumulative percent in each sieve with the results from the class averages, and explain any differences.

EXTRA CREDIT:

Go to www.dlese.org.

In the search box, enter a key term (such as “sediments” or “soil.”)

Then from the “Grade Level” box, select “Middle (6-8.)

Select one or more choices in the “Resource Type” box.

Click on the “Search” oval.

Examine one or more of the web sites that are included, and write a one-paragraph description of what you do at the site(s.) Attach your descriptions to your lab report.

If you carry out any of the activities that you find through a DLESE search, you will receive additional credit.

Also, extra credit will be given for submitting a review or comment using the links in the upper right corner of the listing page.