How life and Earth have changed each other

Grade 9 Science Worksheet - Challenge Me

Circle the best answer.

1. 1.

   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?

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

2. 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.

3. 2.

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

   • The corals lived at 1,400 m depth, deep in the dark sea where they were found
   • Currents carried the corals down to 1,400 m after the reef formed there
   • The reef grew upward as the island sank, so life and Earth changed together
   • The sea once stood 1,400 m higher, so the corals grew at the surface
4. 3.

   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: 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
   • No: the air held no oxygen until land plants appeared
   • Yes: oxygen jumped to 21% within a few thousand years of the first microbes
5. 4.

   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: minerals are only 45%; the 5% organic part comes from living things
   • 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: roots, microbes and humus are 50%, as much as water and air

6. Three planets' air (NASA)

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

7. 5.

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

   • No: Earth's air is 21% oxygen and 0.04% CO₂, unlike its neighbors, because of life
   • Yes: the three airs are alike, so life cannot have changed any of them
   • No: Mars has the most oxygen, so life made its air
   • Yes: Earth's air differs from its neighbors just because it is closer to the Sun than Mars
8. 6.

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

9. Card

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

10. 7.

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

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

11. 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.

12. 8.

    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 10 billion tonnes, a small fraction of 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

13. Events (approximate, millions of years ago)

    Event	Millions of years ago
    Microbes' oxygen fills the air	2,400
    Land plants spread	470
    Roots form deep soil and forests	385
    Buried swamp plants form coal	300

14. 9.

    Ari reads the table. Which summary of how life and Earth changed together fits all four events?

    • Earth changed first, and life just responded to it; life did not change Earth in return
    • The four events happened within a few thousand years of each other
    • Life changed the air; the air opened land to life; plants then changed soil and rock
    • Soil formed from rock alone, so roots changed nothing about Earth

15. Rates of change (example data)

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

16. 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 5 m and soils about 10 cm per 1,000 years, so the processes run at very different speeds
    • Reefs add about 50 m and soils about 1 m per 1,000 years, so both are fast
    • Reefs and soils both add about 5 m per 1,000 years, so they run at one speed
    • Reefs add about 10 cm and soils about 5 m per 1,000 years, so soils are faster