Earth's Interior Flashcards
What are the three basic divisions of Earth’s interior?
The crust, mantle, and core—established by gravity and chemical differentiation.
How did density affect Earth’s layering?
Denser materials (like iron) sank to form the core, while lighter materials formed the crust.
What is the Moho?
The abrupt change in seismic velocity marking the boundary between the crust and the mantle.
How do seismic waves help reveal Earth’s interior structure?
Their refraction and reflection at discontinuities indicate changes in composition and density with depth.
What does the P-wave shadow zone indicate?
It shows that seismic waves slow down and refract at boundaries, suggesting a distinct layer (the core) below the mantle.
What does the absence of S-waves in the shadow zone imply?
S-waves cannot travel through liquids, indicating that the outer core is liquid.
What is Earth’s average density and how does it compare to crustal rocks?
Earth’s average density is about 5.5 g/cm³, while crustal rocks range from 2.6 to 3.3 g/cm³.
What does seismic tomography provide?
Three-dimensional maps of seismic velocity variations that correlate with changes in density and temperature
How do oceanic and continental crust differ in composition?
Oceanic crust is mainly basalt, while continental crust is more granitic (ranging between basalt and granite).
What is isostasy?
The state of gravitational equilibrium where denser crustal sections sink and lighter ones rise, similar to objects floating in water.
What generates Earth’s magnetic field?
Convection currents in the liquid outer core (dynamo theory) create and sustain the magnetic field.
What is the geothermal gradient?
The rate at which temperature increases with depth—averaging 20–30°C per km in the crust and much lower in the mantle.
Why is mantle convection important?
It transfers heat from Earth’s interior outward and drives the movement of tectonic plates.
What are the main sources of Earth’s internal heat?
Radioactive decay, heat from the crystallization of the inner core, and residual heat from Earth’s formation.
How do experiments at high pressure and temperature help us understand the mantle?
They simulate mantle conditions to determine mineral behavior and properties (e.g., density, seismic velocities) that match observed data.
