Features of the ocean floor
Grade 9 Science Worksheet
Circle the best answer.
Read this first
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.
Bo uses the card for sea floor 36 million years old. About how deep is it?
- About 4,600 m
- About 2,506 m
- About 2,850 m
- About 15,100 m
Using the same card, how old is sea floor that is 6,000 m deep, by Esme's math?
- About 294 million years
- About 17 million years
- About 10 million years
- About 100 million years
Sonar line across a trench (example data)
Distance along line Depth 0 km 5,000 m 100 km 5,100 m 160 km 9,600 m 200 km 9,800 m 260 km 2,000 m Kira compares the two sides of the trench. Which side is steeper, and by how much on average?
- Neither; both sides span 60 km, so they are equally steep
- The 200 to 260 km side, at 7,800 m per km against 4,500 m per km
- The 100 to 160 km side, at 75 m per km against 130 m per km
- The 200 to 260 km side, at 130 m per km against 75 m per km
Sonar line across a ridge (example data)
Place Depth West 300 km 3,900 m West 100 km 3,100 m Crest 2,600 m East 100 km 3,100 m East 300 km 3,900 m Luz reads the symmetrical profile. Which interpretation fits the table?
- New floor forms at the crest and spreads both ways, deepening as it cools
- Old floor sinks at the crest, so both sides lie deeper than the crest
- The sides are trenches, since depth increases away from the crest
- The crest is the oldest floor, so the younger sides sank into deeper water
Card
NOAA says abyssal plains cover about 70% of the ocean floor. Example, rounded: ocean floor 361 million km²; all land 149 million km².
Milo compares plains with land. About how many times larger than all the land are the abyssal plains?
- About 2.4 times
- About 70 times
- About 1.7 times
- About 0.6 times
Card (example)
Fine sediment settles from the water onto the sea floor, filling low spots first and burying small hills. Young floor near a ridge has had little time to collect sediment.
Why is an abyssal plain flatter than a mid-ocean ridge, by Pia's reasoning?
- Thick sediment buries the bumpy rock on the plain, while the young ridge is bare
- Waves from the surface wear the plain flat over millions of years of motion
- A plain forms where plates collide and press the floor flat under their weight
- Plates move faster under a plain than under a ridge, which smooths the rock flat
Card (example data)
Young, hot rock near a ridge has a density of 3.28 g/cm³. Cool, old rock far from the ridge has a density of 3.34 g/cm³. Both float on the same mantle.
Why does young floor stand higher than old floor, by Ren's reasoning?
- Young floor is heavier than old floor, so it presses the mantle upward and rises
- Old floor is thinner than young floor, so it rides lower on the mantle below it
- Young rock is hotter and less dense, so it floats higher on the mantle
- Young floor is pushed up by plates colliding at the ridge crest and piling up
Card (NOAA)
Mauna Kea rises 13,803 feet above sea level and extends 19,700 feet below it. Mount Everest rises 29,035 feet above sea level.
Which mountain is taller from base to summit, by Tala's reading, and by how much?
- Everest, by about 15,232 feet, since it rises higher above sea level
- Mauna Kea, by about 4,470 feet
- Mauna Kea, by about 62,535 feet, adding Everest's height to its own
- They are equal, since both stand on solid rock
Mauna Kea rises 13,803 feet above sea level and extends 19,700 feet below it. What share of Mauna Kea's height from base to summit is above sea level, by Zee's math?
- About 41%
- About 70%
- About 59%
- About 14%
The Challenger Deep is 35,876 feet deep. Mount Everest is 29,035 feet tall. By what percent is the Challenger Deep's depth greater than Everest's height, by Ari's math?
- About 24%
- About 124%
- About 19%
- About 6,841%