How Earth formed and separated into layers

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   If early Earth had never become hot enough to partly melt, what would the model predict, by Jun's reading?

   • The same layers as today
   • Little sorting, so no distinct iron core
   • A much thicker crust, about 2,000 km deep
   • Iron would float to the top

2. Read this first

   Density (NASA)

   Planet	Density (kg/m³)
   Mercury	5,429
   Earth	5,514
   Mars	3,934

3. 2.

   Mercury has a very high density for its size (5,429 kg/m³, NASA). What does the sorting model suggest about it, by Kira's reading?

   • Its magnetic field makes it dense
   • It did not form layers
   • It likely has a large iron core
   • It must be made of light rock
4. 3.

   Luz's friend says Earth formed with its layers already in place. Which response is best?

   • Disagree: the layers formed later, as iron sank through hot Earth
   • Disagree: Earth has no layers
   • Agree: planets form fully layered
   • Agree: the core was added last

5. Table, Earth's layers (USGS), with columns Layer, Thickness, State

   Crust, about 5 km (oceans) to 30 km (continents), solid, brittle; mantle, about 2,900 km, hot, semi-solid rock; outer core, about 2,200 km, liquid iron-nickel; inner core, about 1,250 km, solid iron-nickel.

6. 4.

   Milo's cousin says the crust is the thickest layer because we stand on it. Which response is best (USGS)?

   • Disagree: the crust is far thinner than the mantle
   • Disagree: the inner core is liquid
   • Agree: the crust is the densest layer, since it holds the iron
   • Agree: the crust is thousands of km deep
7. 5.

   Studies suggest Earth's core had mostly formed within its first tens of millions of years. What fraction of Earth's 4.54-billion-year age is 50 million years, by Pia's math?

   • About 50%
   • About 11%
   • About 0.01%
   • About 1%

8. Radii (NASA, USGS)

   Body	Radius (km)
   inner core	1,221
   Earth	6,375

9. 6.

   The inner core's radius is about 1,221 km (NASA); Earth's radius is about 6,375 km. What fraction of Earth's volume is the inner core (radius ratio cubed), by Ren's math?

   • About 50%
   • About 19%
   • About 3.7%
   • Under 1%
10. 7.

    Plate tectonics recycling crust into the mantle. Why are no rocks left from Earth's first few hundred million years, by Tala's reading (USGS)?

    • Earth formed just 4 billion years ago
    • Earth had no crust until recently
    • The first rocks sank into the core as heavy iron long ago
    • Plate tectonics has recycled Earth's oldest rocks

11. Model planet (model data)

    Quantity	Density (kg/m³)
    average	3,000
    surface rock	3,000

12. 8.

    A planet's average density equals its surface rock's density. What would that suggest, by Zee's reading?

    • A liquid inner core
    • Little or no dense iron core
    • A huge iron core
    • A crust thousands of km thick
13. 9.

    The outer core shown frozen solid. If Earth's outer core cooled and froze solid, what would happen to the magnetic field, by Ari's reading?

    • It would grow stronger
    • It would weaken, since the moving liquid makes it
    • Nothing; the inner core is already liquid
    • Nothing would change, since the crust makes the field
14. 10.

    Four evidence cards, labeled A to D. Which evidence best supports the sorting (differentiation) model, by Bo's reading?

    • Each layer having the same makeup
    • The crust being the densest layer
    • A dense metal core under lighter rocky layers
    • A crust thousands of km thick