Core-mantle boundary

Definition

The core-mantle boundary is the interface that separates the Earth's outer core, which is composed mainly of liquid iron and nickel, from the overlying mantle, made primarily of silicate rocks. This boundary plays a crucial role in understanding seismic wave behavior, as it marks a significant change in material properties that affects how seismic waves propagate through the Earth.

5 Must Know Facts For Your Next Test

1. The core-mantle boundary is located about 2,900 kilometers (1,800 miles) below the Earth's surface.
2. Seismic waves behave differently when they reach the core-mantle boundary due to the transition from solid mantle material to liquid outer core, causing P-waves to continue while S-waves are absorbed.
3. This boundary is also significant for understanding the Earth's magnetic field generation, as the flow of molten iron in the outer core creates electrical currents.
4. The temperature at the core-mantle boundary can reach up to 4,000 to 5,000 degrees Celsius (7,200 to 9,000 degrees Fahrenheit), significantly affecting the physical properties of materials at that depth.
5. Studying seismic waves that reflect or refract at the core-mantle boundary helps geologists map the structure and composition of the Earth's interior.

Review Questions

• How do seismic waves change behavior when they encounter the core-mantle boundary, and what does this reveal about Earth's internal structure?
  • When seismic waves reach the core-mantle boundary, their behavior changes significantly due to the difference in material properties between the solid mantle and the liquid outer core. P-waves can travel through both solid and liquid but slow down and change direction at this boundary, while S-waves cannot pass through liquids at all, resulting in their disappearance. This difference provides critical information about the Earth's internal structure and indicates that there is a fluid layer beneath the solid mantle.
• Discuss the implications of temperature and composition changes at the core-mantle boundary on seismic wave propagation.
  • The high temperatures at the core-mantle boundary influence how seismic waves propagate through different layers. The extreme heat causes materials to behave differently; for instance, while the mantle is solid, it becomes more fluid-like as one moves into the outer core. These temperature-induced changes affect wave speed and energy transmission, leading to variations in how seismic waves are recorded on the surface and allowing scientists to infer details about both composition and phase transitions at this critical interface.
• Evaluate how research on the core-mantle boundary contributes to our understanding of Earth's magnetic field dynamics.
  • Research on the core-mantle boundary is vital for understanding Earth's magnetic field dynamics because this boundary is where liquid outer core convection generates electrical currents. These currents produce a magnetic field through a process known as dynamo action. By studying how seismic waves interact with this boundary and mapping its structure, scientists can gain insights into flow patterns in the outer core. This knowledge helps explain variations in magnetic field strength and orientation over time, contributing to our broader understanding of geomagnetic processes.

Related terms

Seismic waves: Waves of energy that travel through the Earth, generated by earthquakes or artificial sources, and are crucial for understanding the Earth's internal structure.

Outer core: The layer of the Earth beneath the mantle and above the inner core, consisting of liquid iron and nickel, contributing to the generation of the Earth's magnetic field.

Mantle: The thick layer of silicate rock located between the Earth's crust and outer core, characterized by its semi-solid state and convection currents that drive plate tectonics.