GEOG Part 3

We know that the outer core of the Earth is liquid because

no S waves are observed crossing it.

The third ________ occurs midway through the core and marks the boundary between the inner and outer core

Lehman discontinuity

The shallowest seismic discontinuity is called the _______ and it marks the base of the crust and start of the mantle where the rock changes to a more dense mix of minerals

Mohorovicic discontinuity (Moho)

a diffuse zone between 100 and 220 km depth where seismic waves slow down before speeding up again. it is inferred to be a zone where the rock of the mantle is partially molten and weak. This zone is called the _______ and the combination of rigid mantle and crust above is called the ______

asthenosphere ("weak layer") lithosphere ("rock layer").

why is the core of earth the hottest ?

because it contains the greatest concentration of radioactive elements and because it is insulated by the mantle

The second seismic discontinuity is called the _________ and it occurs about halfway to the center of the Earth, marking the change from rock to iron metal at the mantle -core boundary

Gutenberg discontinuity

The lithosphere is composed of solid upper mantle and crust. The crust is made of two fundamentally different kinds of rock. ____________ The rock of the lithosphere floats on the weak, plastic rock of the asthenosphere

Thin dense rock forms crust beneath the ocean basins thick, less dense rock forms the continents.

the self-sustaining process responsible for maintaining the Earth's magnetic field in which the kinetic energy of covective motion of the Earth's liquid core is converted into magnetic energy

geodynamo

In the core, even though the inner core is hotter than the outer core, the ________ in the inner core prevents the iron from melting. In the outer core, the melting point of the iron is lower due to less pressure - low enough to allow the iron to melt at the temperatures of the outer core. In the mantle, high pressure prevents the mantle rock from melting except for a narrow layer in the upper mantle where the actual temperature and the melting temperature are nearly equal, causing the rock to be partially molten and weak

pressure

Observing P waves produced by earthquakes reveals that there are three depths at which the P waves suddenly increase in speed and are bent to a different path (refracted).

the Mohorovicic discontinuity the Gutenberg discontinuity the Lehman discontinuity