Reconstructing Early Earth — Drills · Grade 9 Science

Chapter: Earth’s History

What these drills covers

By the end of Reconstructing Early Earth you should be able to:

8 questions, written answer, multiple choice and numeric, each with a worked explanation.

Vocabulary used: accretion, differentiation, geologic record.

Problem 1

Does a young rock prove the planet is young?
Answer and explanation

No. It may record a recent event on an old planet.

Problem 2

Accretion is…
  1. growth by joining smaller bodies
  2. the reversal of gravity
  3. a method for measuring rainfall
  4. the same as erosion
Answer and explanation

growth by joining smaller bodies

Collisions and joining build larger bodies.

Problem 3

Earth is about how many billion years old, to one decimal place?
Answer and explanation

4.6 billion years

About 4.6 billion years, from radiometric dating of meteorites and the oldest Earth minerals.

Problem 4

Earth's earliest atmosphere differed from today's mainly in having almost no
  1. nitrogen
  2. free oxygen
  3. carbon dioxide
  4. water vapour
Answer and explanation

free oxygen

Free oxygen accumulated later, largely through photosynthesis.

Problem 5

Banded iron formations are evidence of
  1. no oxygen ever
  2. rising oxygen reacting with dissolved iron
  3. volcanic eruptions only
  4. meteorite impacts
Answer and explanation

rising oxygen reacting with dissolved iron

Oxygen produced by early photosynthesis precipitated dissolved iron from seawater.

Problem 6

Why is very little rock older than 4 billion years found at the surface?
  1. It never formed
  2. Plate tectonics and erosion have recycled or destroyed almost all of it
  3. It is invisible
  4. It melted last century
Answer and explanation

Plate tectonics and erosion have recycled or destroyed almost all of it

Continuous recycling leaves only rare protected fragments.

Problem 7

Explain how scientists study a period for which almost no rock survives.
Answer and explanation

They use the few surviving fragments, such as ancient mineral grains preserved inside younger rock, together with meteorites that formed at the same time as the Solar System and have not been reworked. Evidence from other bodies, like the heavily cratered Moon, also constrains conditions. Each line is indirect, so conclusions are stated with the reasoning and the uncertainty attached.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Explain why the rise of atmospheric oxygen is described as a transformation of the whole Earth system.
Answer and explanation

Oxygen produced by early photosynthetic life changed the chemistry of the oceans, precipitating dissolved iron, then accumulated in the atmosphere where it altered weathering of rock at the surface and made aerobic respiration possible. A biological process therefore reshaped the atmosphere, the oceans and the rock record together, which is why it is treated as a change to the system rather than to one part of it.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

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