Layers of The Earth and Plate Tectonics Learn it, know it, love it.
Inside the Earth The inside of the Earth contains four layers: The crust, mantle, inner core and outer core. These layers occur due to physical and chemical differences
Crust The crust is approximately 32 KM thick. (20 miles) Made up of aluminum, silicon, and oxygen. The crust is solid.
Mantle 2900 Km thick (about 1700 miles) Made up of magnesium and iron Plastic-like- has the ability to act like a solid or liquid. Based on pressure.
Outer Core 2270 Km thick (about 1400 miles) Made up of iron and nickel Liquid due to the temperature.
Inner Core 1300 Km thick (780 miles) Iron and Nickel Solid due to the high pressure
Journey to the Center of People used to believe the earth was solid rock with many caverns. Believed there were giant animals and large treasures awaiting explorers. Earth does not have these hollow spaces, but it is not solid rock either. the Earth
Earth s Interior Physical and chemical makeup of the layers changes with depth. Materials increase in density. (That is why the crust floats) Temperature and pressure increase as you go through the earth.
Mantle s 3 layers Based on physical properties Lithosphere- crust and the uppermost part of the mantle. Floats on the next layer Asthenosphere- Convection occurs here. This layer is plastic-like Mesosphere- Mostly solid layer. Heats the asthenosphere.
Convection Currents When a substance is heated, it becomes less dense. This causes the substance to rise. It then cools down, since it is away from the heat source, becomes more dense, and sinks. Heated objects expand, cooled object contract. Think hot air balloon or lava lamp.
Plasticity The mantle has the ability to act like a solid or a liquid. This is based on the amount of pressure applied to the mantle Example: Oobleck.
How do we know about the inside of the earth? We can make some direct observations: crust and magma The interior of the earth cannot be directly observed. We have never drilled through the crust. Scientists gain most of their information through indirect observations or inferences.
Seismic waves These waves travel through the earth when an earthquake happens. Called P and S S waves bounce off the outer core. Since S waves cannot go through liquids, we say the outer core is liquid When an energy wave bounces off an object, we call this reflection.
More on P and S waves The P waves go through the entire earth, but they bend as they go through the different layers. This means the layers must be made of different material. When an energy wave goes through a substance and bends, we call this refraction.
Shadow zone P and S waves can be detected all over the earth. There are zones that cannot detect some earthquakes. These are called Shadow zones. Shadow- when an energy wave is blocked. Shadows show the waves are bending.
Meteorites We say the core is made of iron and nickel, but how do we know that? Most meteorites, rocks from space, are made up of iron and nickel. Scientists think meteorites are the pieces of broken planet cores. So we hypothesize that our core is like other planets.
Plate tectonics Developed in the 1960 s. This theory says that the earth is broken into plates and those plates are moving in different directions and at different speeds.
Plates- the sections that the crust is broken into. (think puzzle pieces) They are made up of the crust and the upper part of the mantle. Called Lithospheric plates. Plates
Plasticity The lithospheric plates float on the asthenosphere and move around. The plates can move together, apart, or side by side.
Continental Drift Idea that the continents were once together in a large landmass called Pangaea and have moved over time. Developed by Alfred Wegener.
Wegener said that Pangaea, which means all land or all earth, broke apart 200 million years ago. Wegener stated that the continents were moving by plowing through the crust. What would happen to the continents if they did plow through the crust? His idea was initially rejected and he was laughed at for proposing it. Big Al!!!!!!
Wegener s Clues Shape- The continents seem to fit together. Fossils- Mesosaurus fossils were found in S. America and Africa. How could a fresh-water lizard be found in both places? Glossopteris- tropical fern found in Antarctica? Climate had to be warmer at one time.
More Evidence Several landmasses show evidence of an ice age. They had to be together to experience this climate change. If the continents were together at one time, then wouldn t the rocks that make up the continents be the same? They are. Mountain ranges in N. America line up with mountain ranges in Europe and Greenland. Mountains in S. America line up with those in Africa.
Life After Wegener Alfred Wegener died on an expedition in Greenland in 1930. Year after his death, scientists found evidence that supported his theory. Ships began mapping the ocean floor using sonar and as they did this, they found many features they did not expect to find.
Sea-Floor Spreading They found the Mid- Ocean Ridge in the Atlantic Ocean. As they tested the rock, they found the rock at the center of ridge was younger than the rock closer to the continents. If the sea-floor all formed at the same time, what should the age of the rocks be?
Sea-Floor Spreading When rocks form at the bottom of the ocean, the magnetic minerals line up with magnetic North (like on a compass) The ocean floor has some rocks pointing to magnetic north and some pointing to magnetic South Why is that happening?
Sea-Floor Still Spreading If the rocks had formed at the same time, all the iron would point in the same direction. Since it is pointing in opposite directions, the rocks formed at different times. Different times means that the sea-floor is spreading. The magnetic field of the Earth will at times switch north to south. This would explain the iron pointing in different directions.
How the plates move Convection occurs in the asthenosphere due to temperature differences in the layer. The mantle is heated, rises, strikes the crust, then cools and sinks back down toward the outer core.
Plate movement The mantle rises because as it is heated, it becomes less dense than the mantle around it. Less dense objects rise The mantle then strikes the crust and it is like rock hitting rock. (oobleck) This constant force of hitting gradually moves the plates 3-4 inches / year.
Types of Plate Boundaries Convergent- When two plates are moving toward each other. Two Possibilities Subduction- When one plate that is weaker buckles under another. Forms trenches in the ocean and volcanic mountains on land. Convergent #1
Convergent (continued) Convergent #2 Collision- Where two continental plates come together. Usually forms high mountain ranges Ex. Himalayas, Appalachians, and the Alps.
Divergent Plates Occurs between plates that are separating. Usually indicates sea-floor spreading. Ex. Mid-Atlantic Ridge Divergent Boundary
Transform Boundary Occurs where plates slide past each other. Localized deformation, low mountains and valleys. Ex. San Andreas Fault
Features of plate tectonics Faults Earthquake and volcanoes Mid-ocean ridges Mountains and valleys Ocean trenches
How do we measure plate movement? Scientists use lasers and satellites to test for plate movement Laser are shot from ground locations to orbiting satellites and they are used to mark the exact ground location of that laser. They are tested each year and measurements are made.
Earthquakes and Volcanoes.
Causes of Earthquakes Elastic Limit- amount of stress an object can absorb and bend before it breaks. When a rock breaks you have a fault Fault- A break in the rock in which both sides of the rock are moving. The break releases energy which causes earthquakes.
Faults Hanging wall is the wall above the fault line. Top is larger than the bottom Footwall is the wall below the fault line. Bottom is larger than the top.
Types of Faults
Normal Fault When a fault moves apart. Caused by tension forces The hanging wall moves down in relation to the footwall. Can form mountains
Reverse Fault When a fault moves together. Caused by compression forces. Hanging wall moves up in relation to the footwall. Also causes mountains
Strike-Slip Faults(Transform) When a fault moves side by side. Caused by shear forces. Does not always have a hanging and footwall Most earthquakes are caused by this fault.
Seismic Waves P, S, and L
Seismic Waves - P and S P waves are faster. S waves are slower. P waves move like a slinky dog. The front shoots out and the back catches up. S waves look like a snake with an up and down motion.
Love Waves When P and S waves combine at the surface of the Earth, you get Love waves. These waves are the destructive waves. Move up and down and side to side.
Parts of a Fault Focus- Where the rock breaks and an earthquake begins Epicenter- The point on the Earth s surface directly above the focus. The epicenter is the most effected area by the earthquake
Locating Epicenters Scientists use seismographs to record P and S waves from Earthquakes. By measuring the difference in P and S wave arrival times, a seismologist can determine the distance to the epicenter. They take three cities and draw circles around those cities. The radius of the circle is equal to the distance they are away from the earthquake. Where the three circles meet is the epicenter. Triangulation
Triangulation
Richter and Mercalli Scales Richter measures magnitude or size and is based on a power of 10 scale. Each earthquake is 10 times greater than the one before. Can be measured during the quake. Mercalli measures intensity or what it felt like. This 12 step scale is based on eyewitness accounts and is used after the earthquake has happened.
Tsunami Large wave caused by an earthquake underwater. The energy wave compresses as it reaches shore. The compressed energy pushes back and causes large waves.
Volcanoes Def- Any opening in the Earth s crust which erupts ash, cinders, lava or bombs. Often forms mountains.
Volcano States Active- has erupted in the past 100 years. Dormant- has not erupted in 100-1000 years Extinct- has not erupted in over 1000 years.
How do volcanoes form? A pocket of magma called a magma chamber forms under the crust. If the pressure and heat are great enough, the magma will force itself up through the crust. Magma that reaches the surface is called lava
Parts of a volcano Magma Chamber- Large pockets of magma that form underground. Pipe- Long, vertical crack in the crust that connects the magma chamber to the vent Crater- Hollowed-out area at the top of a volcano Vent-opening in the crater that tephra emerges from. These are common on top of a volcano, but can also occur on the sides.
Where do volcanoes occur? Volcanoes occur in places directly related to plate boundaries. Volcanoes occur where plates are moving together, moving apart, or at hot spot volcanoes.
Hot Spot Volcano Some areas of the mantle are hotter than others. This hot spot burns through the crust at specific places. The magma hits the ocean and cools. More magma comes out on top of the new rock and eventually may rise up out of the ocean.
Violent or Non-Violent Eruption There are two factors which determine if an eruption is violent: amount of silica in the magma and the amount of water vapor and other gases present in the magma. If gases get trapped in a volcano, they will build up pressure just like a pop can that is shaken. The more pressure, the more violent the eruption. Magma with lots of silica is thick and traps gas and produces violent eruptions. Magma that is silica-poor flows smoothly, traps very little gas, and has quiet eruptions.
Shield Volcano Quiet eruptions Silica-poor magma Broad volcano with gently sloping sides. Looks like shield laying on the ground Hawaiian volcanoes are examples. Lava only.
Cinder Cone Volcano Explosive eruptions Tephra- rock or solidified lava thrown into the air. Cinders, ash, bombs No lava flow, only hardened lava. Steep, loosely packed, tall Paracutin (Farmer)
Composite Volcano Can have quiet or strong eruptions Can release lava only, tephra only, or both. Alternating layers of lava and tephra. Found where subduction occurs. Mt. Saint Helens
Volcanic features Caldera- The top of a volcano collapses after an eruption. Lakes can form if water collects into the caldera Crater Lake in Oregon is an example of a Caldera
Finally the end Pyroclastic flow- large cloud of ash rushes down the side of a volcano. Usually comes from the ash cloud collapsing. Travel 100 mph and the temperature is 1300 degrees F. Ring of Fire- area around the Pacific plate that contains a large amount of earthquakes and volcanoes.