Heat inside Earth and mantle convection
Grade 9 Science Worksheet - Challenge Me
Circle the best answer.
Read this first
Card
Holmes (1930s) pictured plates carried like a conveyor belt on convection cells. USGS now favors slab pull, with ridge push as an added force.
A student tells Esme that plates are only passengers carried by mantle flow. Which reply best uses the card?
- Partly: flow carries heat, but slab pull and ridge push act on plates directly
- Right: the conveyor-belt picture is still the settled view of what moves plates
- Wrong: mantle flow has nothing to do with how plates move
- Right: ridge push is the main force and flow just carries the plates along
Card (example data)
Sunlight warms only the top few meters of rock. The mantle starts tens of kilometers down and is about 2,900 km thick. USGS: its heat comes from decay and from formation.
A student tells Jun that the Sun drives mantle convection. Which reply is best supported by the card?
- No; sunlight cannot reach the mantle, which is heated from within
- Yes; but just in the top 100 km of the mantle, where sunlight reaches
- Yes; surface heat flows down through the crust until the whole mantle churns
- No; the mantle has no heat of its own and pressure alone moves the rock
Card (example data)
a plate moves 3 cm a year. USGS: slow by human standards, but plate motion adds up to thousands of kilometers. 1 km = 100,000 cm.
A student says 3 cm a year is too slow to matter for geology. Which reply works best, by Kira's math?
- In 100 million years it adds up to 3,000 km, enough to open an ocean
- In 100 million years it adds up to 300 km, so the student is partly right
- It matters if the rate speeds up over time
- In 100 million years it adds up to 30,000 km, almost around Earth
Card (example data)
Soup circulates about 1 cm a second. Take 1 year as 30 million seconds. Mantle rock circulates about 2 cm a year (USGS: a few cm a year).
Luz compares the soup model with the mantle. About how much faster is the soup, and what is the model good for?
- About 15 times slower; the soup is the slower flow, so it models speed well
- About 15 million times faster; it shows rise and sink directions, not speed
- About 15 million times faster; it shows speed too, since both flow in cells
- About 15 thousand times faster; it shows speed as well as direction of flow
Card
Model X has separate upper and lower mantle cells. Model Y has cells through the whole mantle. A scan (example evidence) traces cold rock from a trench to about 900 km. USGS: cell structure is unanswered.
Which conclusion about the scan is best supported, by Milo's reading?
- It favors Model Y but does not prove the cell shapes
- It favors Model X, because slabs stop at 700 km
- It says nothing, since a cold slab is not part of convection
- It proves Model Y, so the cell structure is settled
Card
A diagram shows plates carried by cells beneath them, with nothing drawn at a trench or ridge. USGS: slab pull is now favored and ridge push adds.
What is the strongest correction Noah can make to the diagram?
- Replace the cells with a sea of liquid magma lying under the plates
- Show the slab rising at the trench, since hot rock goes up at the edges
- Remove the cells, since heat cannot move solid rock under the plates
- Add a trench slab and a raised ridge, since forces act on plates directly
Card (example)
Between 100 and 200 km earthquake waves slow down. S waves still pass through the zone. The rock there is near its melting point (USGS).
Pia weighs two ideas: the zone at 100 to 200 km is fully liquid, or solid with a little melt. Which evidence on the card matters most?
- The rock is near melting, so it is already liquid
- Waves slow down, which a liquid does and solid rock cannot
- S waves still pass through, which a fully liquid layer would block
- Waves slow down, so the zone is colder than its surroundings
Plate edges and speeds (example data)
Plate Subducting edge Speed Plate P 12,000 km 8 cm a year Plate Q 9,000 km 7 cm a year Plate R 2,000 km 4 cm a year Plate S 0 km 2 cm a year Plate T 10,000 km 2.5 cm a year Which conclusion does the table support best, by Ren's reading?
- Ridge push explains Plates P, Q, R and T equally well, so slabs are irrelevant
- Slab pull helps explain speed, but Plate T shows other factors also matter
- Slab pull alone sets speed, and Plate T is simply a measuring error in the data
- Edge length has no link to speed, since Plate T is slow despite its edge
Sea-floor ages (example data)
Distance from ridge Age 200 km 4 million years 400 km 8 million years 800 km 20 million years 1,200 km 30 million years A student says the rate stayed 4 cm a year (1,200 km in 30 million years). What do the rows show, by Tala's math? (1 km = 100,000 cm.)
- The rate was only 2 cm a year for the first 400 km, then rose to 5 cm a year
- 4 cm a year is only an average; it was 5 cm a year early and slower later
- The student is right; one steady rate of 4 cm a year fits every row of the table
- The rate rose over time, from about 3.3 cm a year up to 5 cm a year
Card (example data)
a plate moves 5 cm a year. It goes 50 km in a million years. USGS: plates move a few centimeters a year.
Which summary links plate speed to time, by Bo's math?
- A few cm a year adds up to hundreds of meters over 100 million years
- A few cm a year gives thousands of km in a single million years
- A few cm a year adds up to thousands of km over about 100 million years
- A few cm a year is too small to add up to any distance