Earth’s Layered Structure (part 2)

The Earth’s Interior We last discussed these points: How we know about the interior of the Earth… How Earth’s interior took on its characteristics The layers of the Earth as defined by composition Today we will discuss: The layers of the Earth as defined by their behavior…

Layers Due to Behavior The Inner Core Solid metal sphere at Earth’s center High pressure maintains solidity even though temperatures are high enough to melt metal Only 1200 km thick

Layers Due to Behavior The Outer Core Liquid, metallic core High temperature creates convection currents Vertical motion in a fluid like boiling water Hot liquids are less dense (and so rise); cool liquids are more dense (and so sink)

Layers Due to Behavior Motion of the liquid metal produces a magnetic field – Earth’s “magnetosphere” Without the magnetic field, Earth would be subjected to deadly radiation from the sun Therefore, without the outer core, there would be NO LIFE on Earth

Layers Due to Behavior The magnetic field is due to the combined properties of the outer core It is metallic AND it is liquid AND in motion ALL THREE are required to produced the magnetic field  For example – Mercury has an iron core, but no magnetic field because it is solid!  Venus has a liquid iron core, but it has no magnetic field because there is very little motion within the liquid

Moving outward - The Lower Mantle The lower mantle is a thick layer of mostly solid rock (over 2200 km thick) However, rock is not rigid – it can flow like a thick liquid (like cold honey) Is responsible for heat transfer from the core outward

Continuing upward - - The Asthenosphere The asthenosphere is part of the UPPER MANTLE It is consider a “plastic” zone – not completely molten, but not really rigid Rocks in the asthenosphere are very close to their melting points and so deform easily Convection in this region is thought to be the driving force of plate tectonics

The Asthenosphere

Finally, The Lithosphere The lithosphere consists of the uppermost mantle and the entire crust It is a solid, rigid layer that is broken into several “plates” Lithospheric plates are large segments of the lithosphere that consist of oceanic and/or continental crust Seven major and many minor plates (has changed throughout Earth’s history) Plates are in constant motion

The Lithosphere

Motion in the Lithosphere In the lower layers of the Earth (core, mantle), motion is dominated by convection (which is circular in motion) At the surface, this motion translates into lateral (sideways) motion of the plates

Motion in the Lithosphere Two basic forces are thought to control plate motion at the surface of the Earth: Ridge-push As new crust is generated at a mid-ocean ridge, the new crust (assisted by gravity) pushes the older crust aside Slab-pull When oceanic crust is forced under continental crust, the suction of the downward slab pulls the rest of the plate toward the trench

Motion in the Lithosphere Both forces act in tandem (together) along with convection to move the plates

Summary – Can you Answer? What are the five layers of the Earth as defined by behavior? Why is the inner core solid? What is the importance of the outer core? What is the major role of the lower mantle? How is the asthenosphere different from the lithosphere? What is the importance of the asthenosphere? What are lithospheric plates? What are the two forces that control plate motion? What is the basic reason for plate motion?