37 terms

Earth Structure

The layers of Earth are based on what two sets of characteristics?
chemical composition and physical properties
What are the two layers that the upper mantle can be divided into?
asthenosphere and lithosphere
What are the physical properties of the asthenosphere?
softer and more flexible
What are the physical properties of the lithosphere?
solid, relatively rigid, composed of crust and upper mantle
What are the two types of crust?
oceanic and continental, continental is thicker
What happens to the atmosphere as you move away from the Earth's surface?
the atmosphere thins
What are earthquakes?
vibrations in the ground caused by the sudden release of energy, convection currents originating from within the core push the hot mantle material up toward the crust
What are surface waves?
vibrations that run along the Earth's surface, vibrating either up and down or side to side, are mostly responsible for the damaged caused by earthquakes
What are body waves?
vibrations that propagate through the Earth's interior
What are the two types of body waves?
P waves and S waves
What are P waves?
propagate through the ground when atoms push their neighbours which in turn push their neighbours, then rebound and move in opposite direction, resulting in alternating zones of compressed and stretched matter
What are S waves?
the motion of the atoms is perpendicular to the direction of the wave's propagation, cannot pass through materials that are fluid
What is the mantle composed of?
solid yet putty like rock that can flow silicate material (2900 km thick)
What is the Earth's outer core composed of?
molten liquid rich in nickel and iron (2270 km thick)
What is the Earth's inner core composed of?
solid, mass of iron (radius 1216 km)
What is the crust composed of?
hardened exterior of Earth (varies between 5 and 50 km thick)
What waves can pass through the Earth's core?
P waves
What waves cannot pass through the Earth's core?
S waves and surface waves
Describe reflection of a seismic wave
when a seismic wave reaches a rock layer boundary and does not cross over, instead the energy is redirected back into the rock layer it has been travelling through
Describe refraction of a seismic wave
when a seismic wave crosses a rock layer boundary, but changes direction in the process
What is the correlation between refraction and layer rigidity?
because seismic waves travel at different velocities within each rock layer they refract towards the layer boundary when their velocity increases upon crossing the boundary BUT refract away form the layer boundary when their velocity decreases upon crossing the boudary
What happens to the velocity of the seismic wave when the rigidity of the rock increases?
the velocity of the seismic wave increases with the rigidity of the rock layer is is travelling through
Generally, where do seismic waves always refract toward?
the surface of the earth
Describe the relationship between the velocity of the seismic waves and the depth of the Earth
the velocity of seismic waves generally increases with depth
What are the four primary zones in the Earth's interior?
crust, mantle, outer core, inner core
What data provided information about the existence of different zones within the Earth?
P wave and S wave arrival times
Why do we believe the Earth's outer core is liquid?
P waves slow down and refract at the boundary between the mantle and the outer core and S waves do not travel through the outer core
Why do geologists believe the inner core is solid?
because P waves refract at the boundary between the outer core and inner core
How could you test whether the core of another planet were completely solid?
set off a bomb to create seismic waves, if S waves arrive on the opposite side of the planet then the core is solid
Which layer of the Earth possesses the greatest thickness?
mantle, containing 82% of the Earth's volume
Which rock best represents the typical composition of oceanic crust?
basalt, is the most common rock type found in the oceanic crust and is the primary reason it is denser then continental crust, the oceanic crust contains an abundance of mafic minerals
Which rock is found in abundance in the continental crust?
granite, contains mostly felsic minerals which give it a relatively low density
What is the major source of energy that drives the movements of the lithospheric plates on Earth?
thermal energy from within the Earth, principally from the decay of radioactive elements
Which layer is the magnetic field of Earth thought to have originated from ?
outer core, because it is iron-rich liquid, the vigorous churning of this material as Earth rotates produces the magnetic field
Why are the lithospheric plates able to move around on the surface of Earth?
because the asthenosphere is composed of weak, hot, dense rock, the cold, rigid, less dense lithosphere is able to float on it
How do we know that the outer core of Earth is liquid?
because a shadow zone exists where S waves do not arrive in the side of Earth opposite the focus of an earthquake, as S waves do not travel through liquid, the shadow zone that exists on Earth indicates that the outer core is liquid
What is the D" layer?
a partially molten layer above the outer core at the base of the mantle, approximately 3000 km beneath Earth's surface, this boundary is observed via the discontinuity in seismic wave velocities at that depth