Evidence for Continental Drift — Drills · Grade 9 Science

Chapter: Earth’s Interior & Plate Tectonics

What these drills covers

By the end of Evidence for Continental Drift you should be able to:

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

Vocabulary used: continental drift, Pangaea, seafloor spreading, paleomagnetism.

Problem 1

Matching fossils on continents now separated by ocean support continental drift because
  1. the animals swam across
  2. the species lived where the land was once joined
  3. fossils move in currents
  4. the fossils are fakes
Answer and explanation

the species lived where the land was once joined

Land species could not cross an ocean, so the landmasses must once have been connected.

Problem 2

Wegener's hypothesis was initially rejected mainly because he
  1. had no fossil evidence
  2. could not explain what moved the continents
  3. had the wrong map
  4. worked alone
Answer and explanation

could not explain what moved the continents

Without a mechanism the idea was hard to accept, however well the coastlines and fossils matched.

Problem 3

Magnetic stripes on the ocean floor are symmetrical about mid-ocean ridges. This shows
  1. the ocean floor is static
  2. new crust forms at the ridge and spreads both ways
  3. magnets were buried there
  4. the poles never reverse
Answer and explanation

new crust forms at the ridge and spreads both ways

Each stripe records the magnetic field direction when that crust solidified, and the mirror pattern shows spreading.

Problem 4

Ocean floor age generally
  1. is the same everywhere
  2. increases away from mid-ocean ridges
  3. decreases away from ridges
  4. is older than the continents
Answer and explanation

increases away from mid-ocean ridges

The youngest crust is at the ridge; it ages as it moves away.

Problem 5

Crust 60 km from a ridge formed when spreading was 3 cm per year. Roughly how many million years old is it, to the nearest million? (60 km = 6,000,000 cm)
Answer and explanation

2 million years

6,000,000 / 3 = 2,000,000 years, about 2 million.

Problem 6

Which is NOT evidence used for continental drift?
  1. Matching coastlines
  2. Matching rock sequences
  3. Matching fossils
  4. Matching present-day weather
Answer and explanation

Matching present-day weather

Current weather says nothing about past positions; ancient climate indicators preserved in rock do.

Problem 7

Explain why sea-floor spreading turned continental drift from a rejected idea into an accepted theory.
Answer and explanation

It supplied the missing mechanism and an independent test. Mapping showed new crust forming at ridges and spreading outward, with symmetric magnetic stripes and ages increasing away from the ridge — a pattern no alternative explained. Wegener's matching coastlines and fossils then fitted into a process that could be measured, which is what moved the idea from suggestion to theory.

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

Glacial deposits are found in rocks now near the equator. Explain what this indicates.
Answer and explanation

Glaciers require cold conditions, so those rocks must have formed when that land lay in a much colder, higher-latitude position. Since climate zones are set by latitude, the simplest explanation is that the landmass has since moved, which is direct evidence for continental motion rather than for a changing global climate alone.

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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