How life and Earth have changed each other

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   Microbes made oxygen for a long time before it built up in the air. Noah looks for the best explanation of the delay. Which fits?

   • Ozone destroyed the oxygen as fast as the microbes made it
   • Oxygen escaped to space, so very little remained in the air
   • Microbes made no oxygen until the delay ended, so nothing built up
   • Early oxygen reacted with dissolved iron and volcanic gases before it could build up in the air
2. 2.

   A, warmer climate, faster weathering, less CO₂, cooler climate; B, warmer climate, less snow, darker ground, more warming. Bo compares the loops. Which statement about their feedback fits?

   • Both loops amplify the warming, since each starts with a warmer climate
   • Loop A damps the warming, while loop B amplifies it
   • Neither loop is a feedback, since each ends in a different system
   • Loop A amplifies the warming, while loop B damps it

3. Read this first

   Card

   Reef-building corals live in sunlit water, mostly shallower than about 50 m. A drill core through an island's limestone cap shows shallow-water coral fossils from the top down to 1,400 m.

4. 3.

   Luz reads the core. What does it show about the reef and the island?

   • Currents carried the corals down to 1,400 m after the reef formed there
   • The corals lived at 1,400 m depth, deep in the dark sea where they were found
   • The sea once stood 1,400 m higher, so the corals grew at the surface
   • The reef grew upward as the island sank, so life and Earth changed together
5. 4.

   A student says oxygen has been 21% of the air since microbes first made it. Jun replies using what is known. Which reply is best?

   • No: the air held no oxygen until land plants appeared
   • No: oxygen stayed far below today's level for a very long time after it first rose
   • Yes: the first microbes set the air at 21%, and it has not changed since
   • Yes: oxygen jumped to 21% within a few thousand years of the first microbes
6. 5.

   Mineral grains, 45; Water, 25; Air, 25; Roots, microbes and humus, 5. A student says soil is just crushed rock. Kira uses the table. Which reply is best?

   • No: organic matter is the largest part, at 45% of the volume of the soil
   • Yes: minerals are the largest part at 45%, so the water, air and roots do not matter
   • No: minerals are only 45%; the 5% organic part comes from living things
   • No: roots, microbes and humus are 50%, as much as water and air

7. Three planets' air (NASA)

   Planet	CO₂ (%)	O₂ (%)
   Earth	0.04	21
   Mars	95	0.17
   Venus	96.5	0

8. 6.

   A student says life only lives on Earth and never changes it. Pia uses the table. Which reply is best?

   • No: Mars has the most oxygen, so life made its air
   • Yes: the three airs are alike, so life cannot have changed any of them
   • No: Earth's air is 21% oxygen and 0.04% CO₂, unlike its neighbors, because of life
   • Yes: Earth's air differs from its neighbors just because it is closer to the Sun than Mars
9. 7.

   Squeeze Earth's 4.54 billion years into one 24-hour day. Oxygen rose 2.4 billion years ago and land life spread 0.43 billion years ago. How many hours apart, by Ren's math?

   • About 12.7 hours
   • About 10.4 hours
   • About 2.3 hours
   • About 21.7 hours

10. Card

    Burying 12 g of plant carbon leaves 32 g of oxygen in the air. (C + O₂ is CO₂ running backward.)

11. 8.

    A coal swamp buries 1 million tonnes of plant carbon. How much oxygen does Tala say is left in the air?

    • About 1 million tonnes
    • About 3.7 million tonnes
    • About 0.38 million tonnes
    • About 2.7 million tonnes

12. Card

    Volcanoes add 250 million tonnes of CO₂ a year and weathering removes 240 million (example data). The air holds about 3 trillion tonnes of CO₂ now.

13. 9.

    Zee adds up the gap for 1 million years with no other change. About how much CO₂ builds up in the air?

    • About 250 trillion tonnes, about eighty times today's total
    • About 0 tonnes, since a feedback loop cancels any imbalance as soon as it appears
    • About 10 trillion tonnes, three times today's total, so feedbacks must balance
    • About 10 billion tonnes, a small fraction of today's total

14. Rates of change (example data)

    Process	Rate (mm per year)
    Coral reef growth	5
    Soil formation	0.1

15. 10.

    Milo turns the rates into change per 1,000 years. Which summary of the pace of life's changes to Earth fits?

    • Reefs add about 10 cm and soils about 5 m per 1,000 years, so soils are faster
    • Reefs and soils both add about 5 m per 1,000 years, so they run at one speed
    • Reefs add about 50 m and soils about 1 m per 1,000 years, so both are fast
    • Reefs add about 5 m and soils about 10 cm per 1,000 years, so the processes run at very different speeds