How life and Earth have changed each other

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   The ozone layer absorbs 98% of UV light (example data). If it thins until it absorbs 96%, by what factor does the UV reaching the ground change for Bo?

   • It barely changes, since 98% and 96% are close
   • It doubles, from 2% to 4% of the UV
   • It rises 2%, from 98% to 100% of the UV
   • It rises by half, from 2% to 3% of the UV

2. Read this first

   Events (approximate, millions of years ago)

   Event	Millions of years ago
   Microbes raise oxygen in the air	2,400
   Land plants spread	470

3. 2.

   Jun links the events. Which chain fits the table, and how long was the gap between the two?

   • Microbes raise oxygen, and land plants spread about 2,870 million years later
   • Microbes raise oxygen, and land plants spread about 1,930 million years later
   • Land plants spread, and microbes raise oxygen about 1,930 million years later
   • Microbes raise oxygen, and land plants spread about 470 million years later

4. A loop (example)

   Step	Result
   1	more oxygen thickens the ozone layer
   2	a thicker ozone layer lets more plants grow on land
   3	more plants release more oxygen

5. 3.

   Luz follows steps 1 to 3 and returns to step 1. Which description of the loop is correct?

   • No loop: life changes the air once and the air does not change life
   • A damping loop: more oxygen leads to more plants, which remove oxygen
   • A damping loop: a thicker ozone layer slows plant growth, which lowers oxygen
   • A reinforcing loop: more oxygen leads to more plants, which add more oxygen
6. 4.

   A reef grows 5 mm a year while sea level rises 12 mm a year (example data). What does Milo predict for the reef?

   • It keeps up easily, since it grows faster than the sea rises
   • It grows above the sea surface, since coral can outgrow any sea level
   • It falls behind by 17 mm a year and drowns below the sunlit water
   • It falls behind by 7 mm a year and drowns below the sunlit water
7. 5.

   A volcanic island sinks 0.03 mm a year for 30 million years while its reef keeps up (example data). How thick is the limestone cap, by Noah's math?

   • About 900 km
   • About 90 m
   • About 900 m
   • About 9,000 m

8. Table, Three stages of a reef around a sinking island, with columns Stage, Island, Lagoon

   Fringing reef, tall, above water, none; Barrier reef, small, above water, wide; Atoll, gone below the water, ring of reef around it.

9. 6.

   Pia reads the table. In what order do the stages appear as a volcanic island sinks?

   • Fringing reef, barrier reef, then atoll
   • Atoll, barrier reef, then fringing reef
   • Barrier reef, atoll, then fringing reef
   • Fringing reef, atoll, then barrier reef

10. The weathering loop (example)

    Step	Result
    1	warmer climate gives more rain and faster weathering
    2	faster weathering pulls more CO₂ from the air
    3	less CO₂ cools the climate

11. 7.

    Tala follows the loop back to step 1. Why does it help keep Earth's climate from running away?

    • Each warming slows weathering, so CO₂ builds up and cools the climate
    • Weathering does not depend on climate, so there is no loop
    • Each warming causes more weathering and CO₂ removal, which cools the climate and works against the warming
    • Each warming causes more weathering, which adds CO₂ and warms the climate further

12. Weathering of similar rock (example data)

    Plot	Weathering (mm per year)
    Bare rock	0.01
    Rock under a forest	0.04

13. 8.

    Zee compares the plots. What do the data show, and what follows for CO₂ over long times?

    • Roots slow weathering to a fourth, so less CO₂ is pulled into rock
    • Roots speed weathering 4 times, so more CO₂ is pulled into rock
    • Roots have no effect on weathering, so CO₂ stays the same
    • Roots speed weathering 3 times, so more CO₂ is pulled into rock

14. Soil depth after bare rock is exposed (example data)

    Years	Soil depth (cm)
    0	0
    100	1
    500	5
    2,000	15

15. 9.

    Kira finds the rate of each stretch. Which stretch is slowest, and what explains it?

    • After year 500, at about 0.7 mm a year, as deep soil shields the rock
    • After year 500, at about 0.07 mm a year, as deep soil speeds up weathering
    • Years 0 to 100, at about 0.1 mm a year, as bare rock resists weathering
    • After year 500, at about 0.07 mm a year, as deep soil shields the rock

16. Card

    1 Dobson unit (DU) of ozone is a layer 0.01 mm thick at the ground. An ozone hole is a column of under 220 DU.

17. 10.

    Ren brings a 220 DU column of ozone down to ground level. How thick is the layer?

    • About 22 mm
    • About 2.2 m
    • About 0.22 mm
    • About 2.2 mm