SEAFLOOR-SPREADING

Sea Floor Spreading

Introduction

  • Proposed by American geophysicist Harry Hammond Hess in 1960.

  • Utilizes SONAR (Sound Navigation And Ranging) to map the ocean floor.

SONAR Technology

  • SONAR sends pulses of sound waves through water.

  • Waves reflect back when hitting objects (e.g., fish, vegetation, seafloor).

  • The device measures the time taken for the echo to return.

Echolocation

  • Example: Insect-eating bats rely on echolocation due to blindness in darkness.

  • Counterpart: Flying Fox or Giant Fruit-eating Bat also uses echolocation.

Mid-Oceanic Ridge

  • Characterized by "stretched marks" on the seafloor where water is drained.

  • Consists of underwater mountain ranges.

Mechanism of Sea Floor Spreading

  • Occurs at mid-ocean ridges due to the upward movement of magma.

  • Convection currents push magma upward, which liquefies and transforms surrounding rocks.

  • When magma reaches the surface, it cools and pushes older rocks outward, similar to magnetic fields.

New Oceanic Crust Formation

  • Younger materials form new oceanic crust, contributing to the ocean floor's expansion.

  • This process is believed to occur every 200 million years.

Evidence Supporting Sea Floor Spreading Theory

  • Magnetic Strips: Rocks exhibit patterns of magnetic orientation.

  • Spinning Core: Core's magnetic orientation changes approximately every 2,000 years, captured by newly formed rocks.

  • Radiometric Age: Ocean floor rocks are significantly younger than continental crust rocks.

  • Seafloor Drill Data: Different ages and densities of rocks found in layers substantiate the theory.

  • Molten Material Evidence: Rock formations resemble shapes created by toothpaste, indicating molten eruptions.

Quiz Questions

  1. What is the mid-ocean ridge?

    • c. Mountain chains on the ocean floor.

  2. Evidence supporting age differences in oceanic crust?

    • c. The radiometric age of the two layers of oceanic crust.

  3. Proposer of seafloor spreading theory?

    • b. Harry Hess.

  4. True or False: Rocks under the ocean floor align with magnetic lines?

    • a. true.

  5. Why does the seafloor spread?

    • a. Due to the upward movement of molten materials leading to new oceanic crust formation.