Lecture Notes: Lithospheric Plates and Their Movement

Introduction to Lithospheric Plates

• Clues that indicate movement of lithospheric plates.

Clue 1: Fit of Continents

• Continents appear to fit together (e.g., South America and Africa).
• Initial observation made in elementary geography classes.
• Suggests that continents may have been connected in the past.
• Does not confirm ongoing movement or cause of separation.

Clue 2: Mid-Atlantic Ridge

• Observations from the mid-Atlantic ridge (mountain range in the Atlantic Ocean).
• Presence of underwater volcanic activity contributing to the ridge.
• This alone does not confirm plate movement but raises questions.

Clue 3: Magnetic Rock Evidence

• Over the past 60-70 years, separate discoveries have contributed.
• Examination of magnetic rocks from different geological periods.
  • Rocks align with Earth's magnetic field when molten.
  • If Earth's magnetic field was constant, rock alignment would be uniform.
  • Evidence shows that older rocks can have opposite magnetic alignment.

Fluctuations in Earth's Magnetic Field

• Conclusion that Earth's magnetic field fluctuates over time.
• Relevance to plate tectonics:
  • Rock formed at mid-Atlantic ridge aligns with current magnetic field.
  • Further from the ridge, rocks show alternating magnetic alignments (symmetric patterns).

Conclusion on Plate Movement

• The symmetric magnetic striping indicates that rocks were once connected.
• Supports the hypothesis that the rift has moved apart over time.
• Definitive evidence of plate movement identified in the 1960s.

Future Implications

• Plates moving towards each other can lead to subduction zones.
• Future discussions will cover theories on why plates move.

Modern Measurement of Plate Movement

• Use of GPS satellites to measure plate movement.
• Movement is generally slow (1 cm/year, akin to fingernail growth).
  • Some plates may move faster (up to 10-15 cm/year).
• GPS provides precise data on the movement of different plates.

Conclusion of Lecture

• Next lecture will delve into theories explaining the movement of tectonic plates.