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Footprints in a Split Valley: Clues From a River Cleanup

Grade 7 earth science: a river cleanup leads to rift valley rocks, dinosaur tracks and sea-floor ages that show North America and Africa split apart.

Grade 7ScienceInteractive · Printable

Aligned toMS-ESS2-3

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What’s included

Single worksheet
Auto-graded online
1 NGSS standard
Printable answer key
10 questions
Classroom-ready

Details

Format: Interactive · Printable
Grade: Grade 7
Subject: Science
Question types: Fill in the blank, Multiple choice, Circle the answer, Sorting, Short answer

About this worksheet

What students practice

Students compare rock and fossil data from two valleys to argue they were once part of one landscape.
Students use a modern rift valley and sea-floor ages as evidence that two continents moved apart.

How to use

Use after introducing plates; read the passage aloud, compare Tables 1 and 2 together, and let students write the final argument on their own.

Curriculum

NGSS standard covered

MS-ESS2-3

Use fossil, rock and seafloor data as evidence of past plate motions.

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Footprints in a Split Valley: Clues From a River Cleanup

Compare rocks, a modern rift and the Atlantic sea floor to find evidence that continents moved apart.

Two valleys, one story?

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

Cleanup Day on the Tamsett River

1Every April, volunteers from Brookfield Middle School's watershed club spend a Saturday pulling trash out of the Tamsett River, which drains a long valley in the eastern United States. This year, club member Lucía Vang noticed that the rocks along the river change as you walk downstream: first ridges of dark, hard basalt, then reddish sandstone, then crumbly black shale. On a flat slab of red sandstone beside the trail, she found a line of three-toed dinosaur footprints.

2The club's guide that day was Dr. Wendell Asare, a geologist with the state survey. He explained that the valley's rocks lie in layers. The black shale formed from mud on the bottom of old lakes and holds fossils of lake fish. The red sandstone formed from sand and mud along lake shores and riverbanks, where dinosaurs walked. The basalt formed from lava flows that spread across the valley floor. A huge fault runs along the eastern edge of the valley, where the valley floor dropped down thousands of meters compared with the hills beside it. Below all of these layers lies gneiss, a much older, folded rock.

3Back at school, Dr. Asare showed the club a report on a valley in northwest Africa, across the Atlantic Ocean (Table 1). Then he compared the Tamsett Valley with the East African Rift, a long valley in eastern Africa where Earth's crust is being pulled apart today (Table 2). In that rift, the valley floor keeps dropping along big faults, volcanoes erupt, long lakes fill the low ground and earthquakes are common. GPS stations show the two sides of the rift moving apart a few millimeters each year.

4Finally, Dr. Asare described the floor of the Atlantic Ocean between the two valleys. A long underwater mountain chain, the Mid-Atlantic Ridge, runs down the middle of the ocean, and most of the ocean's earthquakes happen along it. The ocean floor is youngest at the ridge and gets older toward each coast. The oldest ocean floor, next to each coast, is about 180 million years old. Today the two valleys are about 5,000 km apart.