Geology 101: Chapter 3: Earth's Interior

Describe the two fundamentally different types of crustal rock.

granitic rock is typical of continents, while basalt predominates in ocean basins.

Describe the internal structure of the earth.

the earth's interior is divided into 3 layers. The crust- a thin skin at the surface. The mantle- a thick shell of rock beneath the crust which extends down to the core, a central sphere; almost 1/2 the diameter of the planet.

What do big quakes provide?

they provide valuable information as their shock waves radiate through the earth.

Geophysics

uses indirect techniques to deduce the composition and behavior of the interior of the earth.

describe xenolith's. (where do they come from? etc..)

xenolith's come from eruption lava that carry with it fragments of rock torn from the walls of volcanic conduits. Some xenolith's come from the mantle. In the process huge slices of mantle rock have been brought to the surface by tectonic activity.

What is an ophiolite?

A section of oceanic crust on land; those unusual rock slices are called ophiolite's. which is a sequence of rocks that geologist interpret as being a cross section through the oceanic crust. (part of earth's crust that underlies the ocean's. 3-5km thick.

gravimeter

a measuring instrument for measuring variations in the gravitational field of the earth

How deep have we drilled into the earth, relative to it's size?

about 8km, the deepest is being drilled and is planned to be 15km in depth, which is 1/4 of 1% to the center of the Earth.

Oil wells act as what to Earth's interior?

act as vital windows

what are seismic waves?

are like sound waves in air; they move in 3 dimensions, where the seismic waves encounter rock layers of differing densities, the waves reflect off the boundaries between the layers.

Why are ophiolites of special interest to geologists?

because they are the easiest eat to see into the earth's mantel; the crust of the ocean's is much thinner than the crust on the continents, so it's easier than looking at continents. Ophiolite's are a chance for geologists to peek down 3-4km deep in the earth and actually be looking at the mantle. So ,apart from xenolith's, walking across a complete ophiolite section is the only other way geologists have of directly viewing rock from earth's mantel.

What is the difference between p waves and s waves

both can pass through solid rock, but only p waves can also pass through gasses and liquids.

Facts about the two types of crust:

continent crust is thicker than the oceans; continents are about 25 and 40 km thick, while ocean crust is between 5 and 10km thick.

what are the two varieties of crust? And what are their differences?

continental crust- forms all large land masses oceanic crust- underlies all the great ocean basins. The difference between thee two types of crust is that their both made up of different types of rock.

How often does earth's magnetic field reverse?

every 500,000 years

During a time of reversed polarity...

lines of force run the other way, going from north to south. The magnetic pulls switch places.

what is continental crust made up of?

made of materials that have been swept together during dynamic processes on the Earth including igneous rocks from volcanic and magnetic events, sedimentary rock, metamorphic rocks.

During a time of normal polarity...

magnetic lines o force leave the Earth near the south pole and re-enter the Earth near the north pole.

How is earth's magnetic field used to study the earth?

mariners found load stone useful for navigating

What is oceanic crust made up of?

more primitive (more uniform); largely iron, magnesium, silicates, has some structures but less than continents.

approximately when was the last reversal?

occurred 700,000 years ago, but research suggests there has been 12 dozen reversal's that could have occurred since then.

Other than seismic waves, how else can people see the interior of the earth?

people create their own earth-shaking devices; shaking the earth.

What concerns do geologists have about future field reversals?

"How long can earth go without a magnetic field?" "How does a reversal affect animals?" "Does the loss of field strength cause an increase in deadly solar radiation?"

Solar Wind

(also known as the northern lights)- is a constant flow of electronically charged particles known as the solar wind. Solar Wind is mostly defeated from earth by our planets magnetic field. These particles are drawn magnetically toward earth's surface, as hitting atmosphere they are gases that glow (red, white and green lights called aurora)

The deep Soviet well penetrates rock as pressures...

5000x that of the earth's surface and at temp. of 300 degrees centigrade

Magnetic Polarity

Direction of the Earth's magnetic field

How was it discovered that the magnetic field of earth could reverse itself?

In the 1900's geophysist's studying lava flows found the lava's and the baked soils underneath them were both permanently magnetized, and their magnetic polarity was identical in orientation. But that orientation was exactly opposite that of the earth. The magnetic north pole of the rocks pointed toward the magnetic south pole of the earth.

What happens to P and S-waves when they reach the core of the earth?

P-waves pass through both mantle and core, but are slowed and refracted at the mantle. S-waves passing from the mantle to the core are absorbed because shear waves cannot be transmitted through liquids.

Describe the two basic types of seismic waves.

Primary or "P" waves- a compressional wave that makes the rock vibrate parallel to the direction of its movement traveling 4 to 7km per second. first wave to arrive at a recording station. Secondary or "S" waves- has a sheering motion that makes the rock vibrate perpendicular to its path, and this movement slows the wave; travels at 2 to 5km per second, half the speed of the p wave and that's why the s wave arrives in second.

What are seismic waves recorded on? What do they allow geologists to see?

Recorded on seismographs during earthquakes, allowing geologists to see how long they take to travel down to the boundary refract off it and return to the surface.

Describe reflection and refraction.

reflection- seismic energy bounces off the boundary between rock refract- or bend, is behaving like light waves, they bend from one rock layer to the next.

What information can geophysicists get from the study of seismic waves?

scientists can learn more about the deep structure of the earth.

How do geophysicists use this difference to study the interior of the earth?

shadow zones depending on which wave. For example the "S" wave leave a much larger shadow zone because none of them pass through the core given that "s" waves cannot travel through liquid, this helps geologist see that at least part of the Earth's core is liquid.

What is paleomagnetism?

study of magnetic fields; lava flows of differing ages preserve evidence of a number of previous magnetic reversals. they are like tape recordings.

Geophysicist's methods

studying seismic vibrations from earthquakes, analyzing variation in the Earth's temperature, magnetic field and gravity and using laboratory and computer models to stimulate conditions deep within the earth.