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what does dynamic mean?
Of or relating to energy or to objects in motion.
what is Earth’s Formation?
Like the rest of the planets in our solar system and beyond, Earth is thought to have begun as a ball of small particles of condensed materials pulled together by gravity. This material accumulated in a process called accretion as smaller bodies collided with larger ones, forming still larger masses of material.
what does Collision mean?
As smaller bodies collide with larger bodies during accretion, the larger bodies not only absorb the material of the smaller bodies they also absorb their energy of motion in the form of heat.
what does Gravity mean?
As a body becomes larger it is increasingly affected by gravitational forces and the interior becomes more and more compressed. This compression of inner materials also produces heat.
what does Radioactive decay mean?
Radioactive decay of elements such as uranium, potassium, and thorium also produces heat, just as it does today.
what is Earth’s Structure?
The combination of Earth’s rotation, gravitational forces, and heat gain and loss resulted in the creation of the different layers that form Earth’s structure.
what is the crust?
The crust is the outermost part of Earth below the atmosphere and hydrosphere (oceans), and although it is the portion of Earth’s structure with which we are most familiar and from which we extract many of our resource needs, it is the smallest of Earth’s layers. The crust is thinnest under the oceans (about 5 km) and thickest under continents (as much as 60km under mountain ranges). The continental crust consists mostly of granite-like rocks while the oceanic crust is composed mostly of basaltic rocks.
what is the Mantle?
Because the deepest drill holes only extend 10-12km into Earth’s crust we do not have direct observations of what lies beneath the crust. However, observations of characteristics and events within the upper layers of Earth have allowed scientists to infer information about the interior.
what is the moho?
A key observation was made by a Croatian scientist named Andrija Mohorovicic as he studied the speed of earthquake waves toward Earth’s center. He noted that at a certain depth the speed of the earthquake waves suddenly increased, and he hypothesized that this marked an interface or boundary between the crust and a layer of a higher density. This layer is now recognized as the boundary between the crust and the mantle; the interface has been named after its founder (in an abbreviated way) and is called the Moho.
­what is the Lithosphere?
Immediately below the Moho the rocks of the upper mantle become rigid and more dense, and are mafic in composition. This stiff, uppermost portion of the mantle and the crust together make up the lithosphere, which extends from the surface to depths of as much as 100km.
­what is the Asthenosphere?
Another portion of the mantle has been characterized based on additional observation of earthquake waves. It was observed that these waves (called seismic waves) decreased in velocity when they reached depths of 100 – 700 km below Earth’s surface. Because this kind of behavior would be expected to occur as the waves traveled through a fluid-like medium, it is believed that the asthenosphere, which is the portion of the mantle immediately below the lithosphere, behaves somewhat like a liquid.
what is the ­Mesosphere?
The majority of the mantle lies below the asthenosphere, and is composed of the same ultramafic materials. This lower portion of the mantle is hotter but stiffer, and stronger because it is under higher pressures. All together the entire mantle (upper mantle, asthenosphere, and mesosphere) extends to 2900km below Earth’s surface.
what is the core?
Further analysis of how seismic waves travel through Earth’s interior revealed another boundary or interface at a depth of 2900km and yet another at 5100km. These two layers have been identified as the Outer and Inner Cores.
­what is the Outer Core?
This layer is thought to be composed of a mixture of iron and nickel, and to be in a liquid state since the earthquake waves that can not travel through fluids are unable to pass through it. The boundary or interface between the outer core and the lower mantle is called the Gutenburg Discontinuity (or the Gutenburg for short).
­what is the Inner Core?
Although the composition of the inner core is not significantly different than the outer core, it seems to be a solid based on observation of seismic waves. This also makes sense given the extreme pressures experienced at the center of Earth; even though temperatures are high enough to melt the inner core, there just is not enough room for atoms to move around as freely as they would need to be able to in a liquid state.
what is Plate Tectonics?
The theory of plate tectonics is known as a unifying theory because it brought together many puzzling observations with explanations that were based on supporting evidence. The ideas supporting plate tectonics evolved over many years and under different names.
what is Continental Drift?
In 1912 a German meteorologist and astronomer named Alfred Wegener proposed that Earth’s continents had been joined as a single landmass at one point in time and that they had since separated and “drifted” over Earth’s surface. He cited several forms of evidence for his theory:
­what is Matching Shorelines?
From the earliest days of mapmaking people had noticed how well the shorelines of North and South America fit with the shorelines of Europe and Africa. Wegener proposed that this was not a coincidence but that they once were joined in an ancient supercontinent he named Pangaea.
­what are Geological Structures?
Wegener compared different landforms on both sides of the Atlantic and found striking similarities. He found that a mountain range in South Africa lines up with a mountain range in Argentina, and that Brazilian coal fields match identically with coal fields in Africa. Matching pockets of rock types and rock sequences can be found in Brazil and the west coat of Africa, and similar correlations can be found between North America and Europe.
what are­ Fossils?
Wegener identified different fossils of both plants and animals that are only found South America and southern Africa.
what are Past Climates?
Wegener pointed out the clear evidence that the different continents had once been exposed to very different climates. Deep scratches in bedrock indicated that portions of southern Africa had once been covered in glaciers. The presence of coal fields in Antarctica indicate that it was once much closer the equator and part of a climate that supported tropical swamps.
what is Sea Floor Spreading?
Wegener’s ideas were not well accepted in the geology world. Scientists could not envision how the continents would “drift” through the solid rock of the ocean floor. Further evidence needed to be gathered from the ocean floor itself. A Princeton University geology professor named Harry Hess used evolving technological advances such as sonar to closely study the ocean floor and to propose the theory of sea floor spreading.
­what are Mid-Ocean Ridges?
New views of the ocean floor came to light following WWII, revealing a continuous chain of undersea mountains that passes through nearly every ocean and circles Earth like seams on a baseball. Hess had observed these ridges and noted the steep mountains with the deep rift or valley running down the middle, and that in many places the valleys are sites of the most active volcanic eruptions. He proposed that magma rises to Earth’s surface in the valleys of these mid-ocean ridges and cools when it reaches the ocean, forming a new strip of lithosphere.
­what are Rock Ages?
Radioactive dating of samples of ocean rocks showed that the youngest rocks are found near the mid-ocean ridges, and that the age increases with distance from the ridges. The oldest rocks are the rocks that form the continental crust.
what are Patterns of magnetic polarity?
When rocks rich in iron form, their crystals align with the direction of Earth’s magnetic field. Because Earth’s magnetic field has been reversed many times (on the order of every 100,000 years), rocks formed at different points in time will be aligned differently. Sensitive instruments used to measure the magnetism of rocks near the mid-ocean ridges were able to detect “stripes” of rocks with normal polarity alternative with rocks exhibiting reverse polarity.
what are Ocean trenches?
are deep underwater canyons where the ocean floor bends downward sharply. Oceanic crust is destroyed in the trenches in a process called subduction
what is ­Subduction?
Subduction is the process in which the ocean floor sinks back into the mantle and melts. Subduction zones, and the ocean trenches which contain them, tend to be found at points where oceanic plates meet continental plates. The denser oceanic plate sinks under the continental plate and is pulled into the mantle to melt. The less dense continental plate does not sink, but instead crumples due to the pressure of the oceanic plate, forming mountains.
what is Driving Force?
While most scientists accept the major part of the plate tectonic theory, there is debate over what makes the plates move. Many scientists believe that heat and gravity, the same key players in Earth’s formation, have a strong role here as well.
what is ­Convection?
Heat flows in three ways, radiation, conduction, and convection. Each of these types of energy transfer requires certain conditions to be successful:
⬢ Radiation occurs best through the vacuum of space or through air or glass, none of which apply to Earth and its rocks.
⬢ Conduction transfers heat energy through molecule to molecule collisions, and so is most effective within solids where molecules are close together. This is how heat moves through solid rock, but it is a slow process.
⬢ Convection transfers heat energy by actually moving hot fluid from one place to another. Warmer fluids are less dense than colder fluids, and so they tend to rise, bringing heat energy with them. As the distance from the heat source increases the heated fluid begins to cool, the density increases, and it begins to sink again, only to repeat the cycle as it returns to the heat source. In this way a convection cell is set up, and scientists believe that these cells form within the semi-fluid asthenosphere and are sufficient to bring heated mantle material to the surface at the mid-ocean ridges and to pull crust back into the mantle at the ocean trenches.
­what is Ridge Push?
A related hypothesis is that rising magma at the mid-ocean ridges pushes the plates apart simply by continually forming new rock layers and then breaking them apart again as newer layers form.
­what is Slab Pull?
A different hypothesis is that the heavier oceanic crust is pulled downward as it sinks into the mantle in the subduction zones. In this hypothesis gravity is the primary force for tectonic plate movement.
what are Plate Boundaries?
The lines along which plates meet and interact are called plate boundaries. As plates meet at these boundaries they can interact in three ways. They can separate (diverge), collide (converge) or slide by each other (transform). Most of the major events involving Earth’s crust, such as mountain building, earthquakes, and volcanic eruptions, occur at plate boundaries.
what are ­Divergent Plate Boundaries?
When two plates meet but are separating the boundary is called divergent. An underwater divergent boundary can be found in a mid-ocean ridge, where rising lava cools to form new rock layers. As these new layers repeatedly form the plates on either side of the ridge are pushed apart. If a divergent boundary is found on land it is called a continental rift valley, and will be surrounded by rugged mountains. For both the mid-ocean ridge and the continental rift valley, divergence also results in many earthquakes and volcanic activity.
what are ­Convergent Plate Boundaries?
When two plates meet and collide the boundary is called convergent and the results can be dramatic. There are three types of convergent plate boundaries:

• Both plates have oceanic crust on top – when plates of this type converge the denser of the two will sink under the other, forming a subduction zone. In these regions we would expect to find ocean trenches and also volcanic island arches. These volcanic island arcs are formed as magma formed from the subducted plate breaks through Earth’s solid surface and forms a series of volcanic islands. Subduction zones are also sites of very deep earthquakes and regional metamorphism crustal rocks.

• Both plates have continental crust on top – when plates of this type converge the two will experience crumpling and thickening of the lithosphere, forming young mountains. The Himalayas in Asia are young mountains still be formed as the India plate collides with the Asian plate. This type of mountain growth is called orogeny.

• One plate has oceanic crust and one has continental crust on top – When these types of plates collide the denser oceanic crust will subduct under the continental crust, again forming an ocean trench. In this case the magma that forms will not create a volcanic island arc because the continent is above the region of magma formation. Instead a relatively new mountain range of young mountains will form, and like the mountains in western Washington and Oregon they may be volcanic.
­what are Transform Plate Boundaries?
When two plates collide by sliding past each other the boundary is called a transform plate boundary. The stresses which build up at these boundaries cause rocks to fracture, forming faults and causing earthquakes. The San Andreas fault in California is caused by the Pacific plate sliding past the North American plate.
what are Earthquakes?
Earthquakes are characterized by a sudden trembling in the ground, and more than one million are estimated to occur each year. The causes of earthquakes are linked to movement of the tectonic plates.
what are earthquake Causes?
Most earthquakes occur when stress builds along of zone of weakness or a break in the rock known as a fault. Stress on rocks is created by forces such as gravity, by expansion and contraction of rock material due to heating and cooling, and by convection currents in Earth’s mantle. There are different types of stress and they produce different effects:

­ Tension – Tension stresses act on a rock by trying to pull it in opposite directions.
­ Compression – Compressive stresses act on a rock by trying to squeeze it together from opposite sides.
­ Shear – Shear stresses may either push on a rock or pull on it, but they do so along different lines and the effect is twisting or tearing
­So how does faulting cause earthquakes?
This is explained by the elastic rebound theory. This theory states that rocks exposed to stress will bend and bend as much as they can before their strength is finally exceeded and they suddenly break, with the two broken edges snapping, or rebounding, back into place.
what are Transverse waves?
Are the kinds of waves we observe at the ocean or when we snap a rope. The wave moves in one direction, but the particles through which the wave is moving do not move with the wave. Instead they move up and down or side to side in a plane perpendicular to the direction of the wave energy, ending up back where they started after the wave has passed through.
­what are Longitudinal waves?
These waves are sometimes called compression waves. When these waves pass through a material the particles move back and forth in the same direction in which the wave is traveling.
how do you ­Measure Earthquakes?
The most reliable measures of earthquakes are made with seismographs. As shown in Figure 3-3, a seismograph consists of a pen attached to a heavy weight that is attached to a spring. During an earthquake, the weight will remain relatively stable because the spring absorbs much of the shaking. The drum in contact with the pen, however, will experience all of the shaking, and it will move while the pen makes marks. The resulting graph is called a seismogram.
what are P-waves?
The P in P-waves stands for primary, but it can also stand for “push-pull”, because P-waves are longitudinal waves. P waves travel the fastest and are therefore the first to reach a seismograph. Notice in Figure 3-3 on the previous page that P-waves tend to have smaller amplitude than S-waves. P-waves can travel through solids, liquids, or gases, but they travel the fastest through solids (about 8 km/sec).
what are S-waves?
The S in S-waves stands for secondary, but it can also stand for “snakey” because S-waves are transverse waves. S-waves travel more slowly than P-waves, thus they are the second waves to arrive at a seismograph after an earthquake. S-waves can only travel through solid materials (about 4 km/sec).
­how do you Locate an Earthquake’s Epicenter?
Knowing the speeds of P-waves and S-waves allows us to determine how far away an earthquake’s epicenter is from our seismograph. If the epicenter is very close to our seismograph we would expect to see the P-wave arrive first but the S-wave to arrive very quickly after it since neither wave had to travel very far. But the farther away we are from the epicenter, the greater the time gap between when the P-wave arrives and when the S-wave arrives.
how do you determine the distance to the epicenter?
1. Use the seismogram to determine the arrival times of the P-wave and the S-wave
2. Subtract to find the difference in arrival times. You can express this in minutes and seconds.
3. You need a paper strip and the Travel Time chart on p. 11 of the ESRT. Place the paper strip vertically along the y-axis and make two marks to show the difference that you calculated.
4. Keeping the paper strip vertical, line up the lower mark on the paper strip with the P curve and slide to the right until the upper mark touches the S curve.
5. Read the epicenter distance on the x-axis that corresponds to that time difference.
how do you locate the epicenter?
To find the location we would need to draw a circle around our seismograph with a radius equal to the distance we read off the chart and we would know that the epicenter must be somewhere on that circle.
how do you determin the origin time of an earthquake?
If we use the arrival times of the P-waves and S-waves to determine how far away our seismograph is from the epicenter, we can also figure out what time it was when the earthquake occurred.
Wave Behavior
These P-waves and S-waves are the waves that helped geologists understand the interior structure of Earth. As scientists started to closely track seismic waves they noticed that at certain locations on Earth’s surface the P-waves and S-waves arrived sooner than would have been expected, while at other locations the P-waves arrived more slowly than expected and without any S-waves. Even worse, at some locations there were no waves at all!
what are Natural Hazards?
Earthquakes are a natural hazard of life on Earth. Most earthquakes occur at plate boundaries due to the higher incidence of stress in these locations, but evidence has shown that earthquakes can happen almost anywhere.
­how do you Measuring the Damage of an earthquake?
Two scales have been developed to measure the strength of an earthquake. One measures the magnitude of the earthquake and energy released (Richter) and the other measures the intensity (Mercalli).
what is a Richter scale?
The Richter scale measures the energy released in an earthquake and information comes directly from seismograph information. The greater the energy in an earthquake the larger the amplitude of the seismic waves. The Richter scale ranges from 0 to 8.6. The scale is logarithmic, which means that the energy increases in powers of 10. Each increase of 1 unit on the Richter scale means that the energy released in the earthquake has increased by a factor of 10.
what is a Mercalli scale?
The Mercalli scale measures the intensity of an earthquake, and information comes from people who experienced the earthquake and observed the amount of destruction. Mercalli information measures the human impact of an earthquake.
what are Volcanoes?
Volcanoes are formed when lava successively reaches Earth’s surface, forming a significant mound. Volcanoes form where cracks in the crust lead to a chamber of magma. Because the liquid magma is less dense than the surrounding solid rocks and is under pressure, it is squeezed up to the surface. As it reaches the surface it moves faster and gases within the magma expand as pressure is decreased. If the magma is mafic (thicker and higher density) then it may have sufficient pressure behind it to explode through the crack in the crust. If the magma is felsic (thinner and runnier) it may quietly flow onto the surface. The shape of a volcano’s cone will be different depending on differences in the magma.
where are the Zones of Activity of a volcano?
Volcanoes are not evenly distributed on Earth’s surface. They occur in specific locations, very closely aligned with the location of plate boundaries.
what is a Pacific Ocean Basin?
Active volcanoes surround the Pacific Ocean Basin, a zone known as the Ring of Fire, while none of the shorelines of continents bordering the Atlantic Ocean are volcanic. These volcanoes are linked with convergent plate boundaries.
what are Mid-Ocean Ridges?
As mentioned previously, the rifts created at divergent plate boundaries, such as in mid-ocean ridges, also are sites of volcanic activity.
what are Hot Spots?
Some volcanoes also occur far from plate boundaries, such as the volcanic islands of Hawaii. Scientists have proposed that there are long-lasting zones of persistently rising magma at certain locations in the mantle. The portion of a tectonic plate that is on top of one of these hot spots will experience pressure from rising magma, cracking, and lava flow so that eventually a volcano will form. As this portion of the plate slowly moves away from the hot spot, a new portion of the plate takes its place. In this way new volcanoes are constantly being formed and a chain is created. (PAN)

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