Download Chapter 7 Answers

7th Grade Science Chapter 7 Answers
1. Scientists think of the Earth’s layers in terms of composition and physical properties.
2. The 3 layers of the Earth from the exterior to the interior of the Earth are the Crust, the Mantle, and the Core.
3. The crust is the thinnest and outermost layer of the Earth which totals less than 1% of the Earth’s mass.
4. Heavier or denser materials sink, so these pieces sink to the center of the Earth & make up the inner core.
5. The 2 types of crust and their composition are:
Continental – its’ composition is similar to granite and it has an average thickness of 30km
Oceanic – its’ composition is similar to basalt, which is much denser than granite, and has an average
thickness of 5-8 km.
The two types of crust are made of very different materials, 1 is significantly thicker than the other and
because of the different materials of composition oceanic crust is more dense than continental crust. P166
6. The mantle is the thickest, “in the middle” layer of the Earth and contains most of the Earth’s mass.
7. The core is at the center of the Earth and is roughly the size of Mars. P 167
8. The outer core is a liquid.
9. The Lithosphere is the “rock sphere” and the outermost layer and is made up of the crust and upper part of
the mantle it is where we find our tectonic plates.
Asthenosphere is the “weak sphere” and soft layer of the mantle that is made of solid rock.
Mesosphere or “middle sphere” is the strong lower part of the mantle and extends to the core.
Outer Core is the “liquid layer” beneath the mantle and it surrounds the inner core.
Inner Core is the solid dense (remember the denser materials sink to the bottom) center of the planet.
Try and remember “LAMOI” as the order of the structure of the Earth as you work from the outermost layer to
the inner core. P 168-169
10. Life is possible in the layer called the biosphere. P169
11. The pieces of the lithosphere that move are called tectonic plates. P 170
12. Scientists look at seismic waves or “vibrations” that travel through the Earth and help seismologists
determine the structure of the Earth’s interior. Scientists use seismographs to measure these waves.
13. Seismic waves vary depending on the density of the material they are travelling through. The denser the
material, the faster the waves travel. Think about if you have ever watched someone throw a ball or
something into a liquid or something that is not a solid, it slows down as it goes through and does not quickly
come out the other end.
14. The lithosphere is the outer most layer of the Earth that is very rigid and is made up of 2 different parts. It is
also were you find tectonic plates. In contrast the asthenosphere is beneath the lithosphere and is the soft
layer of the mantle on which pieces of the lithosphere actually move.
7th Grade Science Chapter 7 Answers
Chapter 7 section 2
15. Alfred Wegener theorized that continents can drift apart from one another and have done so in the past. He
called this continental drift.
16. Wegener’s theory was unaccepted at first because there was no scientific evidence to support the theory and
scientists could not conceive of any force able to move continents. Evidence that supports continental drift
includes the discoveries of the same plant and animal species found on both sides of the Atlantic Ocean. In
addition similar types of rocks and evidence of ancient climatic conditions have been found on multiple
continents. P 173
17. Pangaea is the name given to the ancient continent. P 174
18. Sea-floor spreading is the process by which new oceanic lithosphere is created as older materials are pulled
away. As tectonic plates spread apart they leave a hole in between the two plates. Magma then rises up to
fill in the hole. Think of it this way, let’s say you have a bowl filled with water and wine corks (or something
else that floats). There are enough corks that only some of them are able to float on top of the water. If you
spread the upper layer of wine corks apart new ones from below would come up and fill in the gap.
19. Sea-floor spreading takes place in mid-ocean ridges. P 175
20. Magnetic reversals are recorded in the ocean floor and are the evidence that supports the idea of sea-floor
spreading. Magnetic reversal is when the Earth’s magnetic poles change place. P 176
Chapter 7, section 3
21. Plate tectonics is the theory that explains both continental drift and sea-floor spreading. The theory states
that the Earth’s lithosphere is divided into tectonic plates that move around on top of the asthenosphere.
22. The 3 possible driving forces are:
Ridge push – this is the process by which an oceanic plate slides down the lithosphere-asthenosphere
boundary.
Convection – this is the process by which hot material within the Earth rises and the cooler material sinks.
This is because when this warm material cools, it becomes denser, and sinks.
Slab pull – This happens when the dense oceanic layer of the lithosphere sinks and pulls the rest of the
tectonic plate up with it. P 177
23. The 3 types of tectonic plate boundaries are Convergent, divergent, and transform.
24. A convergent boundary is where tectonic plates collide into one another. Think of both starting with the letter
“C” and that when things converge onto one another they come together or collide.
25. A divergent boundary is where tectonic plates move away from one another.
26. A transform boundary is where plates slide past one another horizontally.
27. The San Andreas Fault is an example of a transform boundary.
7th Grade Science Chapter 7 Answers
28. The 3 types of convergent boundaries are continental/continental, continental/oceanic, and oceanic/oceanic
collisions.
What happens at a convergent boundary depends on what kind of crust is on the edge of each tectonic plate.
At a: continental/continental collision – the crust buckles and thickens pushing the crust upward.
Continental/oceanic – the ocean plate slides under the continental plate. The oceanic plate sinks down
into the asthenosphere in a region called the subduction zone.
Oceanic/oceanic – one plate slides under the other much like in a continental/oceanic collision.
29. A transform boundary is where we see the sliding and grinding and jerking motion that can produce
earthquakes.
30. Plates collide in convergent boundaries, remember collide=convergent p 178/179
31. A subduction zone can be found in convergent boundaries as well. Remember in convergent boundaries one
plate is pushed under the other, sometimes these sink down into the asthenosphere or the subduction zone.
32. Scientists use a network of satellites called a global positioning system to track the movements of tectonic
plates. P 180
Chapter 7, Section 4
33. When objects are squeezed due to stress like when 2 tectonic plates collide, they experience compression.
This is scene in the Rocky Mountains and the Cascade Mountain Range.
34. Tension is the type of stress that occurs when forces act to stretch an object. You can see this in a Divergent
Plate Boundary. P 181
35. When rock layers bend due to stress you have folding. Think of the photo on p182 showing the Rocky
Mountains and the lines you see. See how it looks like folds that you would find in your shirt.
36. The 3 types of folding that occur due to stress from bending in the rock layers are:
i. Syncline – this is horizontal stress that is shaped like an arch in a downward direction. It is like a hole
or depression in the rock layers or like a valley.
ii. Anticline – this is the horizontal stress that is shaped like an arch but in an upward direction. It is like a
hill in the rock layers.
iii. Monocline – This is the vertical stress that occurs in the rock layers. Remember the stress leaves both
ends of the rock layers still vertical. Think of the book example from p 182.
37. The surface along which a rock breaks and slides past one another is called a fault. The two parts of a fault are
the hanging wall and the footwall.
38. The name given to the blocks on either side of a fault are called fault blocks. p 183
39. A footwall is the fault block that is located below the fault. See the glossary
40. A hanging wall is the fault block that is located above the fault. See the glossary
7th Grade Science Chapter 7 Answers
41. In a normal fault the hanging wall moves down relative to the footwall. Think of it as it is normal for gravity to
act and pull the wall down. Think of when items are pulled away from each other the natural tendency would
be for one of the items to fall to the ground.
42. In a Reverse fault the hanging wall moves up relative to the footwall. Think of it as a reverse of what you
would expect to happen. Think about what happens if you squeeze a banana still in the peel. It naturally
wants to come out the top of the peel. P 183
43. When opposing forces act to cause the rock to break and move horizontally it is known as a strike-slip fault.
Think of the example in the book that you would look out and see that the ground had moved to the left or
right, not up or down. P 184
44. Most of the world’s major mountain ranges form at tectonic plate boundaries.
45. When rock layers are squeezed together and pushed upward, we see folded mountains. Think of the stack of
paper example from the book. Push up on the stack, what happens to the paper is the same as what happens
to folded mountains. P 185
46. Fault-block mountains occur when tectonic forces put enough tension on the Earth’s crust. A large number of
normal faults occur and fault-block mountains form when the large blocks of the Earth’s crust drop down
relative to the other blocks.
47. Volcano’s usually form at convergent boundaries when the molten rock erupts into the Earth’s surface.
Volcano’s form from this new material that is added to the Earth’s surface.
48. The type of mountain that involves huge sections of the Earth’s crust being pushed up into anticlines and
synclines are folded mountains.
49. Continental mountain ranges are usually associated with convergent boundaries. Remember continental
mountain ranges are formed when rock layers are pushed together or collide!
50. Mid-Ocean ridges are associated with divergent boundaries. Remember that mid-ocean ridges are associated
with sea-floor spreading and sea-floor spreading occurs when the crust is pulled apart or away.