1. Lesson 15 – Things you need to know but they are not on the reference table.

2. Density. Density Density is the relationship between mass and volume.
All objects have density and their density remain the same even if you cut the object into smaller pieces.
The only time an object density changes is when the object changes temperature or pressure.
Heat will cause materials to expand, thereby, changing the volume of the object.
Pressure will cause an object to shrink, thereby, changing the volume.

3. Density (cont). Everything in Earth Science deals with density.
The layers of the earth was formed by density. The more dense material sank to the center of the earth and the least dense floats on the surface.
Even the atmosphere is divided into layers based on different densities.
Water has a density of 1. Anything with a density more than one will sink, while anything less than 1 will float.
Saturn is the only planet that can float on water.

4. Plate Tectonics
Plate tectonics is the theory that the Earth’s continents are moving across the globe.
The evidence for this is: the continents fit together like a puzzle, the same rocks and fossils are found on different continents, and cold weather fossils are found on warm continents.
The earth’s crust (lithosphere)is the thinnest layer of the Earth. It is also the least dense.
The crust is broken into several plates. These plates float on the mantle.
Convection currents formed in the mantle push and pull these plates in different directions.
The boundaries of these plates create earthquakes and volcanoes.
Hotspots are ares on the plate where magma can easily push thought.
Unlike volcanoes which are found along the edge of plates, hotspot are found in the center of plates.

5. Plate Tectonics (cont)
There are three type of movements along the plate boundaries:
Divergent
Convergent
Transformed.
At divergent boundaries, plates are moving away from each other creating ridges. As the plates move away, new rock form. When looking at the plates on page 5, rocks near the ridge are younger than the rocks on the other side of the plate.
Also, the plate on the other side of the ridge is a mirror image of the plate you may be looking at.

6. Plate Tectonics (cont)
At convergent boundaries, plates are moving towards each other creating trenches. As the plates move towards each other, they collide. The more dense plate slides under the least dense plate. This is known as a subduction zone or trench.
Mountains and volcanoes are formed at convergent boundaries.
At transformed boundaries, plates are rubbing against each other in opposite directions. Large earthquakes occur at transformed boundaries. The San Andres, located in California is a transformed boundary.

7. Landscapes There are 4 major landscapes that you need to know:
Mountains – Mountains are large layers of rocks that has been pushed upwards by tectonic plate movement. They usually show evidence of folding and/or uplifting.
Plateaus – Plateaus are large areas of flat land that is located at high altitudes. Plateaus are formed when large amounts of magma pushes through the crust a settles between layers of rock. The magma pushes up the land above.
Valleys - Valleys area areas found between mountains. There are two types of valleys:
V shaped valleys, which are formed by rivers.
U-shaped valleys, which are formed by glaciers.
Plains - Plains are areas of flat lands that were formed from sediments from an ancient sea that evaporated or the deposition from a river.

8. Rock Layers There are 3 major types of rock:
Igneous – which is rocks made from melted rock (lava and magma)
Sedimentary - Which is rock made from pieces of rocks cemented together.
Metamorphic - Which is rocks that have change physically due to heat and pressure.
When igneous and sedimentary rock are made, they are made in horizontal layers.
Lava and sediments deposit in horizontal layers. As time passes on, more layers of sediment and/or lava accumulate.
When looking at layers of rocks, the oldest rock in on the bottom and the youngest is on the top.

9. Rock Layers (cont)
Sometimes, these layers of rock are put under a lot of pressure. When this happens, the rock layers may up lift on one side – causing one side to be higher than the other.
In some cases, the pressure is so great that the layers of rock begin to fold; looking like a wave.
In both cases, this immense pressure creates metamorphic rock.
Many times, magma will force its way through crack in the layers, heating the rock around it. This is called magma intrusion. This heating changes the rock around it into metamorphic rock.
Because of tectonic movement and immense pressure, rocks layers crack creating faults. These faults can crack through several layers of rock, allowing rock layers to relocate up or down.
Rock layers exposed to the surface may erode. In many case, the layer is partly eroded leaving some evidence of it existence; but in some cases, the layer is completely gone, with no trace. On a diagram of rock layer, erosion is represented by a squiggly line moving across horizontally.
When looking at layers any folding, uplifting, magma intrusion, erosion and faulting happened after the rocks were layered.

10. Rock Layers – Index Fossils
To get an age of a rock layer, scientist use index fossils.
Index fossils (found on pages 8 & 9) are special fossils used in dating rocks.
What makes index fossils special is that they are only found during a short time in history; which means that if the same index fossil is found at two different location miles away, we can conclude that the layers of rocks are the same age.

11. Weathering, Erosion, Depositation
Weathering – Weathering is the process of breaking down rock. Rock composed of hard minerals weather slower than rocks composed of softer minerals.
Physical weathering is breaking rock into smaller pieces of rock.
This happens as water gets into cracks of rocks and freezing.
This can also happen as wind, sand and water move over the rock, rubbing it away. (like an eraser
Chemical weathering is the breaking down of rock chemically.
The rock is dissolved.
This happen in limestone as water moves through it.
The limestone begins to dissolve creating caves and sinkholes.

12. Permeability
Permeability refers to how easy water can move into the soil.
This is effected be 3 things:
How pack the soil is. The more packed the soil is, the least permeable it is. Soil that has round particles that are roughly the same size is more permeable than soil that has angular particles of different sizes.
The slope. Ground that is flat is more permeable than ground with a slope.
How saturated the soil is. Soil contains lots of holes in it. These holes are referred to as the soil’s porosity. If these holes are filled with water, then new water entering the soil will have a hard time moving through. When the soil’s holes are all filled, it is known as saturated (the soil can cannot hold any more water).
When the soil is saturated, or too tightly packed, or has a steep slope, rain water will move along the surface of the ground rather than through it. This is known as runoff.

13. Rivers
Rivers are bodies of water that move water from one place to another.
Water always move from high elevations to low elevations. The steeper the slope, the fast the water moves; the flatter the slope, the slower the water moves.
Fast moving water tends to erode more than slow moving water.
Slow moving water tends to deposit more than fast moving water.
Curvy rivers – Rivers that are curvy has two processes happening at the same time – erosion of the outer banks of the curve and depositation on the inner part of the curve.
The river is shallow towards the edge and deep in the middle because of the speed in which the water moves.

14. Rivers
Because of the speed (velocity) of the moving water, rivers can hold a lot of sediments.
If the water is moving fast, than it can move all types of sediments including stuff like boulders and cobbles. But once the river slows down, it starts to drop sediments starting with the large sediments first.
When the river is moving slow, only small sediments like clay and silt are left in the water.
Deltas (fan shaped land formed at the end of a river) are created as moving rivers come to a stop as they enter the ocean.
When looking at sediments on the bottom of a river, you will see that the sediment is sorted by size (largest on the bottom and smallest on top) and the sediment has rounded edges (because of all the banging as the sediment came down the river).
Glaciers sediments are different. The sediment is unsorted and mixed up. The sediment is also rough and angular.
River
Glacier