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Lesson 1: Spherical Earth
A. Describing Earth
1. Scientists see the shape of Earth in pictures taken by satellites.
2. These pictures show that Earth is not quite a perfect sphere, which has all points on the surface at
an equal distance from the center.
3. Instead, Earth looks like a slightly flattened ball, with a(n) bulge at the equator.
B. Earth Systems
1. Earth has four systems that interact with each another.
2. Earth’s outermost system is the atmosphere, which is made up of the layer of gases surrounding the
planet.
3. Earth’s hydrosphere includes all the water found on Earth’s surface, below ground, and as a liquid in
the atmosphere.
4. As water moves between the air and Earth’s surface forming raindrops or evaporating from puddles,
the atmosphere and the hydrosphere interact.
5. Earth’s entire solid body is called the geosphere.
6. All the living things on Earth form the biosphere.
C. How did Earth form?
1. Earth and the rest of our solar system formed from a large cloud of gas and dust.
2. Gravity made the material in the cloud come together to form the Sun and the rest of the solar
system.
3. Gravity is the force that every object exerts on every other object.
a. The strength of gravity depends on the amount of mass in objects. It also depends on the
distance between objects.
b. The more mass two objects have, the stronger the force of gravity is between them.
c. The closer two objects are to one another, the stronger the force of gravity is between them.
4. Objects near Earth’s surface fall to the ground because Earth’s gravity pulls objects toward the
center of the planet.
D. The Solar Nebula
1. The solar system formed from a cloud of material called a nebula.
2. Because of the force of gravity, the cloud shrank, flattened into a disk, and began to rotate.
3. The material at the center of the rotating disk became a star that we call the Sun.
4. The remaining bits of material around the star formed planets, including Earth.
E. Early Earth
1. As Earth grew, it heated up inside. Its rocks softened and began to flow.
2. Gravity pulled surface bumps toward Earth’s center. Earth began to look like a sphere.
F. The Formation of Earth’s Layers
1. Thermal heat inside Earth melted some of the materials that formed Earth.
2. These liquid materials were able to move, or flow, and form layers.
3. Earth’s layers formed because of differences in density of the materials.
a. Density is a measure of the mass of a material per unit of volume. The denser a material is
the more mass it has per unit volume.
b. The force of gravity caused denser materials to sink toward the center of Earth.
c. The least dense materials stayed at the surface of the planet.
d. The materials that had intermediate density formed the middle layer of Earth.
Lesson 2: Earth’s Interior
A. Clues to Earth’s Interior
1. Scientists explore the geosphere by going into deep mines.
2. Scientists learn about the inside of Earth by sending down instruments and bringing up rock samples
from wells.
B. Temperature and Pressure Increase with Depth
1. The deeper you go below Earth’s surface, the higher the temperature is.
2. The deeper you go below Earth’s surface, the higher the pressure is.
3. The pressure increases because of the weight of the overlying rocks.
C. Using Earthquake Waves
1. Scientists learn about Earth’s interior by studying waves from earthquakes.
2. These waves move in different ways through different kinds of materials.
D. Earth’s Layers
1. The crust is the brittle, rocky outer layer of Earth.
2. Earth’s outermost layer is similar to the shell of an egg: It is the thinnest layer.
3. There are two types of crust—continental crust and oceanic crust. Continental crust is much thicker
than crustal rocks under the oceans.
E. Mantle
1. Below the crust is the mantle, the thick middle layer of Earth.
2. The rocks of the mantle are denser than crustal rocks.
3. Scientists group the mantle into four different layers.
a. The topmost layer of the mantle is a rigid layer called the lithosphere.
b. The rocks in the mantle’s second layer are so hot that they melt and become plastic, which
means that they begin to flow.
c. The layer of melted rock in mantle is the asthenosphere.
d. The lowest two layers of the mantle are solid because great pressure in these layers
prevent(s) the rock from melting.
e. The upper mantle and lower mantle form the largest of Earth’s layers.
F. Core
1. Earth’s core is the dense, metallic center of the planet.
2. The central part of Earth is made of metal. When the planet was young, these dense materials
melted and were pulled by gravity toward Earth’s center.
3. Earth’s core has a(n) outer layer that is liquid and a(n) inner layer that is solid.
4. The inner core spins a little faster than the rest of Earth. It is made of iron crystals.
5. The core causes a(n) force field to form around Earth.
G. Earth’s Magnetic Field
1. The movement of molten iron in Earth’s core makes the planet act like a giant bar magnet, with one
pole near the top of the planet and one pole near the bottom.
2. Over time, Earth’s magnetic field has varied in strength and direction.
H. Magnetosphere
1. Earth’s magnetic field protects the planet against cosmic rays and charged particles from the Sun.
2. The magnetosphere is the outer part of Earth’s magnetic field. It interacts with cosmic rays and
charged particles from the Sun, trapping some particles and pushing away others.
Content Practice B (page 14)
1. A sphere is shaped like a ball, which has all points on its surface at an equal distance from the center.
2. a. atmosphere—the layer of gases surrounding Earth; b. hydrosphere—all Earth’s water, water vapor, and ice; c. geosphere—
Earth’s entire solid body; d. biosphere—all Earth’s living things
3. The solar system developed under the influence of gravity. Gravity pulled together a large rotating cloud of dust and gas called the
solar nebula. The cloud flattened into a disk. Material in the central part of the disk came together under the force of gravity to form the
Sun. Other parts of the disk formed the planets.
4. As the interior of the young Earth heated up, rocks and metals melted. The denser materials, such as iron, sank toward the center of
Earth. The lighter materials formed layers above that.
5. Density is the amount of mass in an object per unit of volume.
Math Skills (page 15)
1. 1 g/cm3
2. 10.5 g/cm3
3. 0.9 g/cm3
4. 30 cm3
5. 180 g
School to Home (page 16)
1. a. The atmosphere is the layer of gases surrounding Earth; b. The hydrosphere is water found on the surface, underground, and as
liquid water in the atmosphere; c. The geosphere is Earth’s entire solid body; d. The biosphere includes all living things on Earth.
2. When the solar system formed about 4.6 billion years ago, gravity caused particles to come together to form spherical Earth. Earth
developed distinct layers based on density—the inner layer contains the densest materials, and the outer layers contain less dense
materials.
Key Concept Builder (page 17)
1. rocks, sediments, soil
2. oxygen gas, nitrogen gas, carbon dioxide
3. clouds, oceans, lakes, glaciers
4. plants, animals
5. energy, matter
6. billion
Key Concept Builder (page 18)
1. satellites
2. sphere
3. gravity
4. mass, distance
5. center
6. gas, dust
7. disk
8. Sun
9. rock
Key Concept Builder (page 19)
1. B
2. D
3. the Sun, because it has the most mass of any object in the solar system
Content Practice A (page 31)
1–7. From the outer dark line to the center: crust, uppermost mantle, asthenosphere, upper mantle, lower mantle, outer core, inner core
8. no check mark
9. check mark
10. check mark
11. no check mark
12. check mark
13. no check mark
Content Practice B (page 32)
1. Possible answer: The shell represents Earth’s crust, the white represents the mantle, and the yolk represents the core.
2. They showed that the deeper you dig, the hotter the temperature gets. This finding indicated that Earth’s interior is very hot.
3. Continental crust is thicker and lighter than oceanic crust. It is made of rock with a large percentage of elements of low mass, such
as silicon and oxygen. Oceanic crust consists of dense rock that contains a large proportion of iron and magnesium.
4. a. uppermost mantle; b. asthenosphere; c. upper mantle; d. lower mantle
5. lithosphere
6. a. outer core—made of hot liquid metal, mostly iron; b. inner core—made of even hotter solid metal, iron
Key Concept Builder (page 34)
1. inner core
2. outer core
3. lower mantle
4. upper mantle
5. asthenosphere
6. lithosphere
7. outer core
8. lithosphere
9. upper mantle
10. asthenosphere
11. inner core
12. lower mantle
Key Concept Builder (page 35)
1. crust and uppermost mantle
2. the yolk
3. The model is uniformly solid, whereas Earth’s core consists of a solid inner core and a liquid outer core.
4. The core is mostly iron, whereas higher layers are made of molten or solid rock.
Key Concept Builder (page 36)
1. The outer core spins faster than the inner core.
2. The movement of liquid iron in the outer core generates a magnetic field around Earth.
3. bar magnet
4. The magnetic field traps or repels electrically charged particles from the Sun.
5. The needle is a magnet. It points toward Earth’s magnetic north pole.
Key Concept Builder (page 37)
1. The deeper you dig into Earth, the hotter it gets.
2. 1
3. They must be very hot.
4. The composition and density of materials making up Earth is different at different levels of the planet.
5. Earthquake waves are affected by different materials they travel through. So, by studying how waves move through Earth, scientists
can determine what Earth’s layers are made of and how dense they are.
6. plastic
7. pressure