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8th Grade Earth Science Packet - PT


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-marked by usually continous and productive activity or change
-of or relating to physical force or energy
Earth's Formation-1
-material accumulated in a process called accretion as smaller bodies collided with larger ones forming still larger masses of material
Earth's Formation-2
Accretion not only produces larger and larger celestial bodies, it also produces heat in three different ways
Earth's Formation-3
Collision- as smaller bodies collides with larger bodies during accretion, the larger not only absorb their energy of motion in the form of heat
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 surface.
The crust is the outermost part of Earth below the atmosphere and hydrosphere, and although it is a portion of Earth's structure with which we are familiar and from which we extract many of our resource needs, it is the smallest of Earth's layers.
The crust is the thinnest under the ocean and the thickest under continents. The continental crust consist of mainly granite-like rocks while the oceanic crust is composed mostly of basaltic rocks.
Because the deepest drill holes only extend 10-12 km into Earth's crust, we do not have direct observations of what lies beneath the crust. Hoever, observations of characteristics and events within the upper layers of Earth have allowed scientist to infer information about the interior.
The Moho-1
A key observation made by a Croatian scientist named Andrija Mohorovicic as he studied the speed of earthquake waves toward Earth's center.
Immediately below the Moho the rocks of the upper mantle become rigid and more dense and are mafic in compisition. 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.
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 100-700km below Earth's surface. Because this kind of behavior would be expected to occur as the waves traveled through a lithosphere behaves somewhat like a liquid.
Scientist believe that the asthenosphere behaves like a liquid and partly like a solid. There are parts of te asthenosphere which consist of molten rock or magma, and this is where sciectist think the lava and magma which form igneous rock originate. The
The asthenospher is believed to be ultramafic with high concentrations of olivine and pyroxene.
The majority of the mantle lies below the asthenosphere and is composed of the some 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 extends to 2900km below Earth's surface.
Further analysis of how seismic waves travel through Earth's interior revealed another boundary or interface at a depthof 2900km and yet another at 5100km. These two layers have been identified as the Outer and Inner Core.
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 unale to pass through it. The boundary or interface between the outer core and lower mantle is called the Gutenburg Discountinuity.
Inner Core-1
Although the composition of the inner core is not significantly different than the outercore, it seems to be a solid based on observation of seismic waves.
Scientist can observe how seismic waves travel through Earths interior to learn about the solid and liquid layers, but they need to make different observations to infer the composition of Earths core.
Scientist can observe that meteorites that fall to Earth are composed of the same type of material from which Earth formed 4.6 billion years ago. These meteorites are highly mafic and contain significant amounts of iron and nickel.
Earths magnetic field also supports the hypothesis of an iron nickel core, since these are two of the few magnetic elements.
A combination of iron and nickel at the temperatures and pressures believed to be in Earth score can account for the observed properties of the core.
Which of the following best characterizes what happens as depth within Earth's interior increases?
Density, temperature, and pressure increase
The rock located between 2900km and 5100km below Earths surface is inferred to be?
an iron rich liquid
Which is the most accurate statement about Earths inerior
The Pressure within the mantle increases with depth
Which zone Earth has the greatest density?
Inner Core
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.
Continental Drift-Main
In 1912 a German meteorologist and astronomer named Alfred Wegener proposed that Earths continents had been joined as a single landmass at one point of time and that they had since separated and "drifted" over Earths surface. He cited several forms of evidence for his theory:
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 his was no a coincidence but that they once were joined in an ancient supercontinent he named Pangea.
Geological Structures-2
He found that a mountain range in South Africa lines up with a mountain range in Argentina and that the Brazilian coal fields match identically with coal fields in Africa. Matching pockets of rock types and rock sequence can be found in Brazil and the west coast of Africa, similar correlations can be found Between North America and Europe.
Wgener identified different fossils of both plants and animals that are only found in South America and Southern Africa.
Past Climates
Wegener pointed out the clear evidence that the different continents had once been exposed to very diffent climates. Deep scratches in bedrock inndicated that portions of southern Africa had once been covered in glaciers. The presence of coal fields in Antarctica indicated that it was once much closer to the equator and part of a climate that supported tropical swamps.
Sea Floor Spreading
Wegeners ideas were not well accepted in th egeology world. Scientist could not envision how the continents would drift through the solid rock of the ocean floor. Futher evidence needed to be gathered from the ocean floor itself. Geology professer Harry Hess, used evolving technological advances such as sonar to closely study the ocean floor and to propose the theory of sea floor spreading.
Mid-Ocean Ridges-1
New views of the ocean floor came to light following WW2, revealing a continuous chain of undersea mountains that passes through nearly every ocean and circles.
Rock Ages
Radioactive dating of samples of ocean rocks showed that the youngest rocks are found near te mid-ocean ridges, and that the age increased with distance from the ridges. The oldest rocks are the rocks that form the continental crust.
Patterns of magnetic polarity
When rocks rich in iron form, their crystals align with the direction of Earths magnetic field. Because Earths magnetic field has been reversed many times, rocks formed at different points in time will be aligned differently. Sensitive instruments used to measure the magnetism of rocks near the mid ocena ridges were able to detect "stripes" of rocks with normal polarity alternating with rocks exhibiting reverse polarity.
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.
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 pointes where oceanic plates meet continental plates. The denser continental plate does not sink, but instead crumples due to the pressure of the oceanic plate, formin mountains.
Theory of Plate Techtonics
The surface of Earth is composed of about a dozen major rigid, movin lithospheric plates and serveral smaller plates. These plates contain areas of light continental rock and the dense oceanic bottoms.
Radiation occurs best through a vacuum of space or through air or glass, none of which apply to Eath 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 enery by actually moving hot fluid from one place to another. Warmer fluids are less dense that colder fluids, and so they tend to rise, bringing heat energy with them.
Ridge Push
A related hypothesis is that rising magma a the mid-ocean ridges pushes the plates apart simply by continually formin new rock layers and then breaking them apart again as newer layers form.
Slab Pull
a different hypothesis is tha thte 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.
Plate Boundaries
lines along which plates meet and interact
transform- slide by each other
Subduction zone
when plates of this type converge the denser of the two will sink under the other
-by a sudden tremblind in the ground and more than one million a year
Causes of Earthquakes
Tension-stresses act on a rock by trying to pull it in opposite directions
Compression-stresses act on a rock by trying to squeeze it together from opposite sides
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
Elastic Rebound Theory
theory states that rocks exposed to stress will bend and bend as much as they can before their strenght is finally exceeded and they suddenly break with two broken edges snapping back into place
where the break occurs
as the broken rock rebounds it pushes against surrounding rocks and releases huge amounts of energy which travel in waves

What are these waves called
seismic waves
Transverse Waves
The wave moves in one directio 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 perpendicular of the wave energy ending up back were they started after the wave has passed through
Longitudinal waves
These waves are sometimes called compression waves. When these waves pass through a material, the particals move back and forth in the same directon in which the wave is traveling
-instument used to measure earthquakes
-results in a seismogram
Body Waves
travel through the body of earth
Surface waves
transport energy alon Eaths surace and play a major role in the damage caused by earthquakes
-p stands for primary
-longitudinal waves
-fastest through solids
-can go thru solids, liquids, gases
-s stands for secondary
-transverse waves
-only travel through solids
Shadow Zones
If the Pwaves approach the outer core straight they can successfully past pretty much straight through the core, but where thhey approach the outer ocre at an angle, they are refracted suffieiently to create shadow zones where neither Pwaves or Swaves are felt
Natural Hazard
Earthquakes are natural hazards of life on Earth.
Richter Scale
measures the energy released in an earthquake
Mercalli Scale
measures the intensity of an earthquake
large wavelength ocean wave produced by a disruption of the ocean floor, frequently from faulting associated with an eathquake, but also from volcanic eruption or a rapid mass movement of large amounts of material
If the magma is mafic then it may have sufficient pressure behind it to explode through the crack in the crust. If the magma is felsic, it may quietly flow onto the surface
Hot spot
long lasting zones of persistenly rising magma at certain locations in the mantle
The most frequent cause of major earthquakes is________?
The immediate result of sudden slippage within Earth's crust is _______?
an earthquake
The source of energy for the high temperatures found deep within Earth is __________?
decay of radioactive radiation
According to the Earth Science Reference Tables, as depth within Earth's interior increases __________?
density, temperatures, and pressure increases.
Two geologic surveys of the same area, made 50 years apart, showed that the area had been uplifted 5 centimeters during the interval. If the rate of uplift remains constant, how many years will be neede for this area to be uplifted a total of 70 centimet
700 years
What is the inferred temperature at the boundary between Earths stiffer mantle and outer core?
5,000 degrees
How do geologists locate the epicenter of an earthquake?
By drwaing circles to show distances from three different seismograph stations. Where the 3 circles meet, is where the epicenter is.
Earth's Formation-4
Gravity- as a body beomes larger it is increasingly affectied by gravitational forces and the interior becomes more and more compressed. The compression of inner materials also produces heat
Radioactive decay of elements such as uranium, potassium, an thorium also produces heat, just ast it does today
The Moho-2
He noted that at a certain depth the speed of the earthquake waves suddenly increased and he hypothesized that this maked an interface or boundary between the crust and a layer of higher density. This layer is now recognized as the boundary between the crust and the mantle; the interface has been named after its founder and is called the Moho.
Mid-Ocean Ridges-2
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 sited of the most active volcanic eruptions. He proposed that magma rises to Earhts surface in the valleys of these mid ocean ridges and cools when it reaches the ocean, forming a new strip of lithosphere.
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 te heat source. In this way a convection cell is set up, and scientist 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.
Inner Core-2
This also makes sense given the extreme pressures experienced at the center of Earth; even though temperatures are high enough to melt the innercore, there just isnt enough room for atoms to move around as freely as they would need to be able to in a liquid state.

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