Features of the ocean floor

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. Read this first

   Card

   Trenches are narrow and 8 to 10 km deep (USGS). They lie beside curved chains of volcanoes. Deep ocean currents move slowly (example).

2. 1.

   A student tells Jun that deep currents carved the trenches. Which reply is best supported by the card?

   • No; trenches form where plates part, and volcanoes then fill the trenches with rock
   • Yes; deep currents carve trenches the same way rivers cut canyons on land, but deeper
   • No; currents cannot cut a trench 8 to 10 km deep beside volcanoes; plate convergence fits
   • Yes; the volcanoes beside trenches are built from the rock that currents eroded

3. Card (NOAA)

   The mid-ocean ridge spans 40,389 miles, about 90% under the ocean. 1 mile is 1.609 km. Example, rounded: the Andes, the longest range on land, stretch about 7,000 km.

4. 2.

   A student tells Kira that ridges are small next to land mountain ranges. Which reply fits the card?

   • No; the ridge is about 65,000 km long, though it lies entirely above the water line
   • Yes; at about 6,500 km the ridge is shorter than the Andes, so it is small by comparison
   • Yes; just the part above water counts as a mountain range, so the ridge is small
   • No; at about 65,000 km the ridge is many times the Andes, but about 90% is underwater

5. Card (example data)

   a submersible descends at 0.5 m per second, explores for 1 hour, then rises at 1 m per second. The average ocean depth is 3,682 m (NOAA).

6. 3.

   Luz plans a dive to the average ocean depth. About how long is the whole trip?

   • About 2.0 hours
   • About 5.1 hours
   • About 3.1 hours
   • About 4.1 hours

7. Card (example, rounded)

   Water pressure rises 1 atmosphere (atm) for every 10 m of depth, on top of 1 atm at the surface. NOAA: average depth 3,682 m; deepest about 10,935 m.

8. 4.

   How much more pressure is there at the deepest point than at the average depth, by Milo's math?

   • About 7,253 atm more
   • About 1,094 atm more
   • About 72 atm more
   • About 725 atm more

9. Card (approximate model, example)

   Sea-floor depth in meters is about 2,500 + 350 × √(age in millions of years). Young floor near a ridge is hot and shallow; it deepens as it cools.

10. 5.

    Floor spreads from a ridge at 4 cm a year. How far from the ridge is floor that is 5,300 m deep, by Noah's math? (1 km = 100,000 cm.)

    • About 320 km
    • About 256 km
    • About 2,560 km
    • About 25,600 km

11. Sea-floor sites (example data)

    Site	Age	Depth
    Site 1	25 million years	4,250 m
    Site 2	49 million years	4,950 m
    Site 3	81 million years	5,650 m
    Site 4	64 million years	4,600 m

12. 6.

    Pia tests the rule depth = 2,500 + 350 × √age (age in millions of years) on four sites. Which conclusion fits the table?

    • The four sites fit the rule within 100 m, so age explains each depth in the table
    • Site 4 is 700 m deeper than the rule predicts, so it is probably the oldest floor of the four
    • Sites 1 to 3 fit the rule; Site 4 is 700 m shallower than predicted, so something lifts it
    • The rule fails at each of the four sites, so sea-floor depth does not depend on age

13. Card (example data)

    a ridge flank deepens 1,400 m over 700 km. The unknown belt beside curved volcanic islands deepens from 4,000 m to 10,000 m over 60 km.

14. 7.

    Which feature is the belt, and why, by Ren's reading?

    • A ridge flank, since depth changes with distance along both of them
    • A continental slope, since it drops steeply beside the volcanic islands
    • A trench: it drops about 50 times more steeply than a ridge flank
    • A trench: it drops about 5 times more steeply than a ridge flank
15. 8.

    Claim: new sea floor forms at a ridge crest and spreads away on both sides. Which evidence would most strengthen the claim, by Tala's reading?

    • The crest's height compared with the heights of other mountain ranges on land
    • Dated rock samples showing that ages rise with distance from the crest on both sides
    • Depth readings along one line that deepen away from the crest on both of its sides
    • A photo of fresh black rock at the crest taken by a submersible, showing new lava
16. 9.

    The average ocean depth is about 3,682 m. The deepest point is about 10,935 m. Which statement does the card support, by Ari's math?

    • The deepest point is about 3 times the average depth and about 14,600 m deeper
    • The deepest point is about 30 times the average depth and about 7,250 m deeper
    • The deepest point is about 3 times the average depth and about 7,250 m deeper
    • The deepest point is about one-third of the average depth and about 7,250 m deeper

17. Card (NOAA)

    Ridges form where plates push apart and magma rises; trenches form where plates converge and one moves under the other; seamounts are volcanic mountains. Sediment settles on abyssal plains.

18. 10.

    Which summary links each feature to how it forms, by Bo's reading?

    • Ridges: plates part. Trenches: wave erosion cuts them. Seamounts: volcanoes. Plains: settled sediment
    • Ridges: plates part. Trenches: plates meet, one sinks. Seamounts: volcanoes. Plains: settled sediment
    • Ridges: plates meet and one sinks. Trenches: plates part. Seamounts: volcanoes. Plains: settled sediment
    • Ridges: plates part. Trenches: plates meet, one sinks. Seamounts: settled sediment. Plains: volcanoes