Which of the following statements regarding what we know about Earth’s interior is most accurate?

1. We have been able to drill into the earth’s core
2. Much about what we know about Earth’s mantle and core comes from caves and mines
3. We know only about what is on the very surface of the earth, in what is known as the crust
4. Energy waves allow us to see precisely what is deep inside the Earth, like a “tricorder” or scanner from Star Trek

Earth’s Interior

What we know about Earth’s interior comes from indirect avenues of investigation.

Earth’s diameter is approximately 12,756 km (~ 7,500 miles).

-the deepest hole we have ever drilled into the Earth is only 9.6 km (~5 mi).

so how do we know what it’s like?

Seismic waves! - natural and man-made

Earthquakes

seismic (energy) waves travel through the earth

some energy bounces off harder layers

called reflection

some energy travels through but gets bent, changing the direction the wave is traveling

called refraction

some energy is absorbed as it encounters materials

called attenuation

Allow us to model what waves show up at given locations, and when they arrive at given locations.

Shallow high frequency seismic waves allow us to see reflectors and refractors at depth

Wave paths are influenced by density, temperature, and the angles at which they strike boundaries as they travel through and around the Earth

Factors affect seismic waves

distance: farther = more attenuation

density: higher = faster

temperature: colder = faster

liquid vs solid

- solid = faster; p-waves and s-waves

- liquid = slower; no s-waves

angle of incidence- controls how much is

reflected and how much is absorbed

vertical arrangement of layers

- controls the resultant direction of travel

P-wave and S-wave shadow zones

- caused by transmissive and refractive properties of the waves interacting with rock and liquid

Zones of material with distinctive characteristics make up each layer in the Earth

Greatly simplified it looks like concentric spheres

Crust- the rigid outer shell of the Earth, composed of solid rock; very thin- averages only 20 km thick (the crust is part of the Lithosphere)

two kinds of crust

Oceanic- most abundant; consists of rocks formed from mafic magma; very dense; very thin- 10 km thick

Continental- underlies continents; consists of rock formed from felsic and intermediate magma; less dense than oceanic crust; thick-30 to 85 km thick

What will happen as different kinds of crust interact with each other?

A) Oceanic and Continental - ?

B) Old Oceanic and Younger Oceanic - ?

C) Continental and continental - ?

Uppermost mantle- Aesthenosphere

Continental crust

Oceanic crust

Mohorovicic Discontinuity

“The Moho”

Model of Lithosphere and Aesthenosphere showing thickness of Oceanic vs Continental crust

Isopach contour lines = lines of equal thickness of the crust

The boundary zone between the crust and the mantle is called the Mohorovicic Discontinuity or the “Moho”

- a zone of low velocity transmission of seismic waves

Mantle- the semi-solid (jello-like) material underlying the crust. Extends down to about 3000 km depth

The uppermost part of the mantle is called the Aesthenosphere.

mostly molten material

The mantle is heated closer to the core

Heated mantle material rises upward very slowly

millions of years to move upward

As it near the earth’s surface, the mantle material liquefies

(due to pressure and temp relationships)

It also begins to cool, and slowly starts to sink back into the core

This creates a Convection current

Two highly schematic models of

mantle convection currents

Heated rising material

Cooled sinking material

3D models of mantle convection currents

3D maps of the earth’s convection currents based on seismic wave analysis-complicated looking!

Earth’s core

Divided into an inner and outer zone

Outer zone is liquid- doesn’t transmit s-waves

Probably composed of Nickel (Ni) and Iron (Fe), some heavier radioactive elements, along with some other elements (S or N- Sulfur or Nitrogen)

Inner core is solid- based on speed of P-wave travel

composed of same materials as outer core

Important for generating Earth’s magnetic field

Earth’s magnetic field is created by the rotation of the outer fluid core around the solid inner core

This creates an

electrical current

Generates an

electromagnetic

Field.

Similar to a

bar magnet with

a positive and

negative end

Earth’s magnetic field fluctuates over time due to the unsteady nature of the geodynamo that is the the outer and inner core

Earth’s magnetic field interacts with solar particles, forcing them to the north or south pole, creating the Aurora Borealis

Earth’s magnetic field plays a vital role in the development of Plate tectonics theory

Identification of a process that allows for Sea Floor Spreading.