Earth and Space

• Explain the movement of tectonic plates in terms of convection currents.

• Evaluate models of the structure of the Earth and tectonic plate movements.

• Explain why the jigsaw appearance of continental coasts, location of volcanoes and earthquakes, fossil records in the Earth’s Crust are all evidence

• for tectonic plates.

• Explain how alignment of magnetic materials in the Earth’s Crust evidence for the movement of tectonic plates.

• Define a scientific Theory.

• Explain how scientists decide to support different scientific theories.

• Describe the evidence for the theory of the formation of the Moon.

Movement of Tectonic Plates – Convection Currents

• The Earth’s mantle contains molten/semi-molten rock (magma) that can flow slowly.

• Heat from the core (radioactive decay + leftover formation heat) causes hot material in the mantle to rise.

• As it rises, it cools near the crust and sinks back down, creating a circular convection current.

• These convection currents drag tectonic plates on the Earth’s crust, causing them to move.

• This movement explains why plates can:

  • Move apart (divergent boundaries) → mid-ocean ridges, seafloor spreading.

  • Collide (convergent boundaries) → mountains, trenches, volcanoes.

  • Slide past each other (transform boundaries) → earthquakes.

Evaluating Models of Earth’s Structure & Plate Movement

• Wegener’s Continental Drift (1912):

  • Suggested continents drifted apart.

  • Evidence: fossil distribution, rock formations, “jigsaw fit” of coasts.

  • Rejected at first because he lacked a mechanism (no knowledge of mantle convection).

• Modern Plate Tectonics (1960s onwards):

  • Combines Wegener’s ideas with discovery of seafloor spreading and paleomagnetism.

  • Now universally accepted because it explains how plates move (convection currents, ridge push, slab pull).

Evaluation:

• Strength: Explains earthquakes, volcanoes, mountains, and distribution of fossils.

• Weakness: Still refining details (e.g., exact forces driving plates, deep mantle behaviour).

Evidence for Tectonic Plates

1. Jigsaw Fit of Continents:

   • South America and Africa coasts fit like puzzle pieces.

   • Suggests they were once joined (Pangaea).

2. Volcano & Earthquake Distribution:

   • Found mainly along plate boundaries (Ring of Fire in Pacific).

   • Matches predictions of plate interaction.

3. Fossil Records:

   • Same species (e.g., Mesosaurus, Glossopteris) found on widely separated continents.

   • Implies continents were once joined.

Magnetic Evidence in Rocks

• As magma cools at mid-ocean ridges, magnetic minerals (e.g., iron) align with Earth’s magnetic field.

• Earth’s magnetic field has reversed many times in history.

• This creates symmetrical magnetic stripes on either side of ridges (palaeomagnetism).

• Proves new crust forms and spreads outward → strong evidence for seafloor spreading and plate movement.

Definition of a Scientific Theory

• A scientific theory is:

  • A well-substantiated explanation of natural phenomena.

  • Based on evidence, experimentation, and observations.

  • Can be tested and modified as new evidence appears.

• Different from a hypothesis (a theory is broader, more tested, and widely supported).

How Scientists Support Different Theories

• Scientists assess theories by:

  1. Evidence – Does it match observations/experiments?

  2. Predictive Power – Can it correctly predict new phenomena?

  3. Peer Review – Other experts check findings.

  4. Reproducibility – Can results be repeated elsewhere?

  5. Simplicity & Coherence – Does it fit with existing scientific knowledge?

• Theories are supported when they consistently explain and predict better than alternatives.

Evidence for the Theory of the Moon’s Formation

• Main accepted theory: Giant Impact Hypothesis.

  • Around 4.5 billion years ago, a Mars-sized body (Theia) collided with Earth.

  • Debris was ejected into space, which eventually coalesced to form the Moon.

Evidence:

1. Rock Composition – Moon rocks brought back by Apollo missions are similar to Earth’s mantle but lack volatile elements (consistent with being formed from Earth debris).

2. Angular Momentum – The Earth-Moon system’s spin and orbit match what’s expected from such a collision.

3. Moon’s Size & Orbit – Too large to be a captured asteroid, and too different in composition to have formed independently.

4. Isotopic Evidence – Oxygen isotopes on Earth and the Moon are nearly identical → common origin.

5. Density of Rocks – The density of the rocks on the moon is less than that of the rocks on Earth