The Dike That Baked the Fossils: Rock Cycle Clues in a Quarry

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The Dike That Baked the Fossils: Rock Cycle Clues in a Quarry

Use shale samples, basalt crystals and a pebble count to model how Earth's materials change and what energy drives them.

Shale beside the dike

Read the passage and Table 1, then answer the questions.

A Day at Kestrel Hill Quarry

1On a Saturday in October, the Earth Science Club from Brookhaven Middle School visited Kestrel Hill Quarry, an old quarry that the state geology survey now uses for field trips. Geologist Dr. Pilar Echeverría led the group. Everyone wore a hard hat and safety glasses, stayed well back from the high walls and collected only loose pieces from the rubble at the base. Seventh grader Arjun Malhotra kept the club's notes.

2Most of the quarry wall is gray shale, a sedimentary rock that splits into thin sheets. It formed from mud that settled on the floor of a shallow sea and was later buried and pressed into rock. The shale holds fossil brachiopods, small shelled animals that lived on that sea floor. A dark band of basalt about 4 m wide cuts straight up through the shale layers. Dr. Echeverría called it a dike: long after the shale formed, magma from deep underground pushed up through a crack in the shale and cooled there into solid rock.

3The club collected shale at five distances from the edge of the dike. For each sample, they tried to scratch it with a steel nail, described it and split it for 15 minutes, counting the fossils they could identify (Table 1). Every sample was bagged and labeled with its distance from the dike. Then they looked at the basalt with a hand lens and measured the average size of its crystals from the edge of the dike to its middle (Table 2).

4At the top of the quarry, above both the shale and the dike, lies a layer of conglomerate. Conglomerate is a sedimentary rock made of rounded pebbles cemented together with sand. Pebbles become rounded as rivers or waves roll them along and knock off their corners. The club broke apart a fallen block of conglomerate and sorted 50 of its pebbles by rock type (Graph 1).

Table 1. Shale Samples at Kestrel Hill Quarry
Distance from dike (m)	Scratched by nail?	What it looks like	Fossils found
0.5	no	dark gray, very hard, faint layers	0
1.5	no	dark gray, hard, clear layers	3
3	yes, with effort	gray, splits into thick sheets	11
6	yes	gray, splits into thin sheets	17
10	yes	gray, splits into thin sheets	18

The 3 fossils found at 1.5 m were blurry outlines of brachiopod shells, with their fine ridges gone.

1.

Which pattern does Table 1 show?

A. The closer the shale is to the dike, the softer it is and the more fossils it holds.B. The shale stays about the same out to 10 m, except that it gets darker near the dike.C. The closer the shale is to the dike, the harder it is and the fewer fossils it holds.D. The shale 10 m from the dike is the hardest, and it holds the fewest fossils.

2.

The sample 10 m from the dike had how many times as many fossils as the sample 1.5 m from the dike? times as many

3.

Which explanation of Table 1 fits the passage best?

A. Rain and wind wore away the fossils near the dike faster than the fossils farther away.B. Heat from the magma changed the nearby shale into a harder metamorphic rock, wiping out most fossils.C. Sea animals stayed away from the dike while they were alive, so few of them became fossils near it.D. The shale near the dike formed later than the rest, after the brachiopods had died out.

4.

The shale beside the dike changed, but it stayed solid and did not melt. Circle the two observations that show it did not melt.

Crystals, pebbles and the rock cycle

Use paragraphs 2–4, Table 2 and Graph 1 to answer the questions.

Table 2. Crystals in the Basalt Dike (the dike is 4 m wide)
Distance from edge (cm)	Crystal size (mm)
0	0.1
50	0.4
100	0.8
200	1.5

5.

The crystals in the middle of the dike are how many times as large as the crystals at its edge? times as large

6.

Why are the crystals smallest at the edge of the dike?

A. The edge crystals are the oldest, so they have worn down more than the others.B. Magma touching the cool shale cooled fast, so its crystals had little time to grow.C. Water seeping along the edge dissolved the large crystals that were there at first.D. The magma at the edge was the hottest, so its crystals melted into smaller pieces.

7.

Use Graph 1 and paragraph 4. What do the rounded basalt and baked shale pebbles in the conglomerate show?

A. After the dike formed, the area was lifted and worn down, and water rounded its pieces.B. Baked shale formed in the conglomerate when sand was pressed around the pebbles.C. The conglomerate formed before the dike, and the magma later pushed pebbles into it.D. The pebbles are pieces of magma that cooled in the air as it sprayed out of the dike.

8.

Which pair of energy sources mainly drove these two steps: (1) baking the shale beside the dike, and (2) rounding the pebbles in the conglomerate?

A. (1) the Sun, through weather and flowing water; (2) the weight of the seaB. (1) the weight of the deep sea; (2) heat from Earth's interiorC. (1) sunlight warming the rock; (2) heat from Earth's interiorD. (1) Earth's inner heat; (2) the Sun, through weather and flowing water

9.

Complete the model of what happened at Kestrel Hill. Use words from the bank. Two words are left over.

Mud on the sea floor was buried and pressed into . Heat from baked the rock beside the crack into rock. Later, uplift and broke these rocks into pieces, and the rounded pebbles were cemented into .

10.

Suppose the conglomerate is buried many kilometers deep and is squeezed and heated for millions of years, but it never melts. What is it most likely to become?

A. A metamorphic rock, with its pebbles flattened and its minerals changedB. A shale full of new fossils from the animals living deep undergroundC. Loose mud and sand again, as the deep heat breaks its cement apartD. An igneous rock like basalt, made of small crystals from cooled magma

11.

A club member says, “The magma melted the shale next to the dike, so the dark rock beside the dike is igneous rock like the basalt.” Do you agree? Write a claim, use evidence from Table 1, Table 2 and the passage, and explain your reasoning with the rock cycle and the energy that drove the change.