Practice Quiz and Review sheet

The practice quiz is on EDU if you haven't seen it yet! fill out the answers on a separate sheet or on there! bring everything you have questions about to class tomorrow.

Here's an outline of the chapters: most of what you need to know for the test is in this summary. We won't have questions about how to measure earthquakes and the other stuff near the end of Chapter 2.

Chapter 1 and 2 Quiz Review Sheet:

How do scientists find out about what is in the interior of the earth?

Seismic waves and evidence from rock that have been brought to the surface of the earth.

After 20 meters, the temperature inside the earth increases by roughly 1 degree Celsius for every 40 meters of depth.

Pressure increases constantly as you go into the earth, because the amount of material above it is pressing down on top of it. Remember that all material within the earth's gravitational influence is pulled by gravity towards the center of the earth.

Layers of the earth:

Crust: Thin, outer layer of solid rock, 5-70 kilometers thick. Not as dense as the other layers of the earth, because it is made up of lighter materials and is exposed to less pressure. Oceanic crust is denser and is thus pulled under continental crust when plates move, creating subduction zones.

Mantle: The thickest layer, the movements in the mantle are responsible for plate motion. Convection currents slowly bring superheated material from the lower mantle up towards the crust, where they cool and begin to sink again. The enormous friction between the powerful (but slow moving!) mantle and the light, thin crust allows the mantle to transport plates on the crust around the globe.

Outer Core: The extreme temperatures within the outer core prevent it from solidifying, and the flow of this liquid part of the earth is responsible for the earth's magnetic field.

Inner Core: The chemical composition and extreme pressure of the inner core cause it to be a solid, even though it is hotter than the outer core.

Heat transfer: 3 types.

Radiation: transfer of heat through the air. Think about when you are on inside dish crew and the Hobart machine is giving off so much heat that you start sweating immediately. That's radiation.

Conduction: Heat transfer within a material or from one material to another that touches it. Think about when you are on inside dish duty and you have pull the hot tray out of the Hobart machine. Touching that tray feels like it will burn you. That's conduction.

Convection: Heat transfer through the movement of fluids (that includes gasses!!). When a material heats up, the particles that make up that material move faster: this spreads them farther apart, making them less dense. Dense materials sink, and less dense materials rise (think about a dense stone sinking in water and a less dense life jacket floating). Therefore, the less dense heated material will rise until it is no longer heated. Then the particles slow down and it becomes denser again. The dense material will now sink back to where it can be heated again. This cycle is called a convection current, and it is important in many areas of earth science, including the movement of the mantle!

Continental Drift:

Early geologists studying plate tectonics noticed that continents separated by wide oceans contained fossils of the same animal. They also found fossils of organisms that could not survive at the latitudes where they were preserved. Finally, the continents looked as though they could be various pieces in a gigantic puzzle. The theory of continental drift was born, and this theory laid the groundwork for the theory of plate tectonics.

Sea floor spreading:

Different scientists noticed a giant mountain range in the middle of the Atlantic Ocean. They realized that this was caused by the divergence of two plates: the gap opened by this divergence allowed magma to well up from deep in the earth and create new sea floor. The other sides of the plates usually subduct under continental plates, creating a constant recycling process that operates like a conveyor belt. Imagine new rock being loaded onto the conveyor belt at the mid ocean ridge, then being transported away to both sides until it sinks underneath a continental plate.

Plate movements and boundaries:

The movement of plates is driven by convection currents in the mantle (remember all that stuff about heat transfer?). The process is very slow, and is made even slower by the fact that every plate is connected to another plate on all sides. This enormous friction causes plates to move slowly, and often means that long periods of no movement are broken up by major movements (which cause faults and earthquakes!).

Remember the velcro analogy: if two plates are well stuck together, it is as though they are velcroed tightly together: you can pull and pull and pull on both sides, and they will not move until you have built up enough pressure to rip them apart. This buildup of friction and energy primes the plate for movement, and the energy is all released in a large movement that often creates an earthquake. This analogy works well for transform and convergent (subducting) boundaries: for convergent plates the velcro would be on top of one plate and on the bottom of the other, and you'd be trying to move one over another. For transform boundaries the velcro would be on the sides of both plates and you would be trying to move them parallel to each other.

3 types of faults:

Faults generally occur at or near plate boundaries: they are the result of stress overcoming the bonds that hold rocks together. The stress breaks the rocks and they move, releasing the stress. Generally, the fault block that moves is called the hanging wall. The side that remains stationary is called the footwall.

Normal faults occur in zones of extension. Divergent boundaries are an example of this extension. Plates pulling apart stretch the crust, and fault blocks drop down because of this thinning.

Reverse faults generally happen at convergent boundaries, where plates are pushing together, compressing the rock. Super stressed rocks will eventually break, and one block will slide over the top of another block.

Strike-slip faults: strike-slip faults usually happen at transform boundaries, where one plate is moving parallel to another plate.

Folds: Often folds form before the stress in rocks is great enough to produce faults. Due to factors such as high temperature, confining pressure, and the slow rate of compression, sometimes rocks bend before they break. Concave down folds (which look like arches) are called anticlines. Concave up folds (which look like the letter U) are called synclines. Though folds can be very small, large anticlines often form mountains, and synclines form valleys.