Heat inside Earth and mantle convection

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 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.

2. 1.

   A student tells Esme that plates are only passengers carried by mantle flow. Which reply best uses the card?

   • Wrong: mantle flow has nothing to do with how plates move
   • Right: the conveyor-belt picture is still the settled view of what moves plates
   • Partly: flow carries heat, but slab pull and ridge push act on plates directly
   • Right: ridge push is the main force and flow just carries the plates along

3. 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.

4. 2.

   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; surface heat flows down through the crust until the whole mantle churns
   • Yes; but just in the top 100 km of the mantle, where sunlight reaches
   • No; the mantle has no heat of its own and pressure alone moves the rock

5. 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.

6. 3.

   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 30,000 km, almost around Earth
   • It matters if the rate speeds up over time
   • 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

7. 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).

8. 4.

   Luz compares the soup model with the mantle. About how much faster is the soup, and what is the model good for?

   • 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
   • 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

9. 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.

10. 5.

    Which conclusion about the scan is best supported, by Milo's reading?

    • It favors Model X, because slabs stop at 700 km
    • It proves Model Y, so the cell structure is settled
    • It favors Model Y but does not prove the cell shapes
    • It says nothing, since a cold slab is not part of convection

11. 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.

12. 6.

    What is the strongest correction Noah can make to the diagram?

    • Replace the cells with a sea of liquid magma lying under the plates
    • 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
    • Show the slab rising at the trench, since hot rock goes up at the edges

13. 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

14. 7.

    Which conclusion does the table support best, by Ren's reading?

    • Slab pull alone sets speed, and Plate T is simply a measuring error in the data
    • 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
    • Edge length has no link to speed, since Plate T is slow despite its edge

15. Card A

    Mantle rock is solid but flows slowly. Card B: Heat comes from decay and from Earth's formation. Card C: Hot, lighter rock rises; cold, denser rock sinks. Card D: The number and structure of cells are unanswered.

16. 8.

    Which summary of mantle convection fits all four cards, by Zee's reading?

    • Interior heat drives slow flow in exactly two loops, as scientists have measured
    • Interior heat makes solid rock flow slowly in loops whose number and shape are unsettled
    • Interior heat makes solid rock flow in loops where the cold rock rises and hot rock sinks
    • Sunlight heats liquid rock so it flows in loops whose exact number is known

17. Card

    USGS now favors slab pull as the main force. Ridge push is an added force. How the forces share the work is still debated.

18. 9.

    Which summary of the forces on plates fits the card best, by Ari's reading?

    • Slab pull alone explains each plate, so the debate over forces is over
    • Winds and tides share the work of moving plates with slab pull
    • Ridge push does the work of moving plates, and slab pull just slows them down
    • Slab pull likely leads and ridge push adds, with the shares still debated

19. 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.

20. 10.

    Which summary links plate speed to time, by Bo's math?

    • A few cm a year adds up to thousands of km over about 100 million years
    • A few cm a year gives thousands of km in a single million years
    • A few cm a year is too small to add up to any distance
    • A few cm a year adds up to hundreds of meters over 100 million years