Worksheet

Slow Mud, Sudden Storms: Reading the Rock in Calder Quarry

Grade 7 earth science: compare slowly built limestone and shale with a storm shell bed, an ash layer and ice grooves to explain changes at different scales.

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1 NGSS standard
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12 questions
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Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Matching, Circle the answer, Short answer

About this worksheet

What students practice

Students calculate and compare how fast rock layers built up.
Students use evidence in rock to explain which layers formed in hours or days and which took thousands of years.
Students explain how processes at different time and size scales shaped one place.

How to use

Read the passage together and sketch the quarry wall from top to bottom; let students do the rate calculations before the discussion of fast layers.

Curriculum

NGSS standard covered

MS-ESS2-2

Explain how geoscience processes at very different time and size scales have changed Earth's surface.

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Slow Mud, Sudden Storms: Reading the Rock in Calder Quarry

Use quarry layers, fossils and ice grooves to explain changes at very different scales.

Layers that built up slowly

Read the passage and study Table 1. Then answer the questions.

A Day at Calder Quarry

1In October, the Fernwood Middle School geology club spent a day at Calder Quarry, where workers cut limestone for roads and buildings. Wearing hard hats and staying well back from the quarry wall, seventh grader Ravi Chandrasekar and the club collected fossils from loose piles of rock with Ms. Henrike Vos, the quarry's geologist. They found crinoids, animals with long stems made of small discs, and brachiopods, animals with two shells, both of which lived on a shallow sea floor. The rocks of the wall are about 370 to 380 million years old.

2Ms. Vos described the layers from top to bottom. Each limestone and shale layer formed from lime mud or clay mud that slowly settled on the sea floor. Over many millions of years, slow movements of Earth's crust lifted the region, and the sea drained away. Using fossils and other clues, geologists have estimated how long the thick layers took to build up (Table 1). Layer A is found under much of the state, not only at the quarry. The flat tops of some shale beds in Layer D are covered with ripple marks a few centimeters apart, like the ones waves make in the sand of a shallow beach, which can form and change within minutes.

3Two thin layers are different. Layer B is a jumble of broken shells with a sharp, flat bottom. The biggest shell pieces lie at the bottom of the layer and the smallest at the top, the way pieces settle when churned-up water calms down. The same layer has been found in quarries 50 km apart. Layer C is soft gray clay made from volcanic ash. Geologists have matched the crystals in it to one eruption of a volcano hundreds of kilometers away, and the same ash layer is found in rock across several states.

4Above Layer A, there is no more limestone. Instead, a layer of jumbled clay, pebbles and boulders, 3 m thick, lies right on top of it. Some boulders are granite, a rock that does not crop out within 600 km of the quarry, and each has a weathered rind about 1 cm thick. Where workers scraped this layer away, the top of Layer A is smooth and scratched with long, straight, parallel grooves. Ms. Vos said a sheet of ice more than 1 km thick covered this region until about 15,000 years ago. Most of the time between Layer A and the jumbled layer is not recorded in the wall at all.

Table 1. Layers in the Quarry Wall, Top to Bottom
Layer	Rock and fossils	Thickness (m)	Time to form (years)
A	Limestone; crinoids and brachiopods	12	about 120,000
B	Broken, jumbled shells	0.3	see paragraph 3
C	Gray clay from volcanic ash	0.05	see paragraph 3
D	Shale; brachiopods, ripple marks	8	about 360,000
E	Limestone; coral fossils	15	about 150,000

12 m is 12,000 mm.

On average, how many millimeters of Layer A built up each year? mm per year

Layer D took how many times as long to form as Layer A? times as long

Which conclusion about Layers A, D and E does Table 1 support best?

A. A thinner layer can take longer to form than a thicker one.
B. Layers A, D and E each built up about 1 mm a year.
C. The thickest layer in the wall took the longest time to form.
D. Shale builds up faster than limestone, so Layer D formed first.

Layers that formed fast

Use paragraph 3 and Table 1.

Suppose Layer B had built up at the same rate as Layer A, 0.1 mm per year. How many years would its 0.3 m (300 mm) have taken? years

Which observation is the best evidence that Layer B formed in hours or days during one storm, not over thousands of years?

A. It holds brachiopod shells, like the limestone of Layer A above it.
B. It is much thinner than Layers A, D and E in the quarry wall.
C. It lies between Layer A and the volcanic ash of Layer C.
D. Its broken shells grade from large at the bottom to small at the top.

Which explanation of Layer C fits paragraph 3 best?

A. Waves broke the shells of Layer B into a fine gray powder that looks like ash.
B. Ash from one large eruption spread over several states and settled within days.
C. Many small eruptions near the quarry dropped ash a little at a time for thousands of years.
D. Gray mud from a nearby river slowly turned into ash as it was buried.

Circle the two layers that most likely formed in a few days or less.

Layer ALayer BLayer CLayer DLayer E

The ice sheet and the missing time

Use paragraph 4 and the whole sheet.

Which explanation of the long, parallel grooves on top of Layer A fits paragraph 4 best?

A. Rain running across the bare limestone wore the grooves in a few years.
B. Storm waves on the ancient sea floor dragged shells across the soft lime mud.
C. Rocks frozen into the bottom of the moving ice sheet scraped across the limestone.
D. Crinoids pulled their long stems across the rock as they crawled along the sea floor.

The top of Layer A is about 370 million years old. The jumbled layer was left as the ice melted, about 15,000 years ago.

About how many million years passed between the top of Layer A and the jumbled layer? million years

10.

Why is so much time missing between Layer A and the jumbled layer, based on the passage?

A. The sea floor stayed under deep water, where little mud settled for millions of years.
B. The rock from that time is hidden behind Layer E at the bottom of the wall.
C. Once the land rose above the sea, rock there was more often worn away than built up.
D. The quarry workers cut away all of the rock that formed during that time.

11.

Match each change to the description that fits it best.

The storm that laid down Layer B
Waves making the ripple marks in Layer D
Lime mud building up Layer A
Weathering the rind on a granite boulder

A. Fast, and covers many kilometers
B. Fast, and makes features a few centimeters across
C. Slow, and covers much of the state
D. Slow, and makes a feature about 1 cm thick

12.

A classmate says, “The rock in the quarry built up at one steady rate. You can tell the age of any layer just by measuring how thick it is.” Do you agree? Make a claim, use at least three numbers from the table, the passage or your answers, and explain how processes at different time and size scales shaped the rock at Calder Quarry.