Name: ______________________________

Science Grade 10 1st Grading

Module 1 – Earth and Space

1. Introduction

Have you ever wondered how did the scientist come up with the knowledge of the
different properties of layers of Earth, how did they know whether that layer is solid
semisolid or liquid.

This chapter revisits and maps out the inner structure of Earth, including its layers and
their distinct properties; it also examines the mechanisms and evidence of plate
movements.

2. Learning Outcomes

After this module the learners should be able to:

1. describe the internal structure of the Earth;

2. explain the possible causes of plate movement; and
3. enumerate the lines of evidence that support plate movement.

3. Lesson 1 – Layers of the Earth

As we all know Earth has distinct layers – the crust, mantle, outer and inner core, and
each layer has distinct properties.

1. Crust

 The Earth's crust is an extremely thin layer of rock that makes up the outermost
solid shell of our planet. In relative terms, its thickness is like that of the skin of an
apple. It amounts to less than half of 1 percent of the planet's total mass but
plays a vital role in most of Earth's natural cycles.

1
  The crust can be thicker than 80 kilometers in some spots and less than one
kilometer thick in others.
 The crust is composed of many different types of rocks that fall into three main
categories: igneous, metamorphic and sedimentary. However, most of those
rocks originated as either granite or basalt.

Two different types of crust

Oceanic Crust

 The crust that underlies the ocean floor

 Has an average thickness of 5 kilometers
 Composed of dense basaltic rocks made up of magnesium silicates

Continental Crust

 The crust that makes up the continents

 Is about 40-70 km thick
 Made up of light granitic rocks which made up of mostly aluminum silicates.

2. Mantle

 semisolid, rocky, and very hot layer

 mostly-solid bulk of Earth's interior
 lies between Earth's dense, super-heated core and its thin outer layer, the crust
 is about 2,900 kilometers (1,802 miles) thick, and makes up a whopping 84% of
Earth’s total volume. As Earth began to take shape about 4.5 billion years ago, iron
and nickel quickly separated from other rocks and minerals to form the core of the
new planet.

2
 The molten material that surrounded the core was the early mantle. Over millions of
years, the mantle cooled. Water trapped inside minerals erupted with lava, a process
called “outgassing.” As more water was outgassed, the mantle solidified.
 The rocks that make up Earth’s mantle are mostly silicates—a wide variety of
compounds that share a silicon and oxygen structure. The other major type of rock
found in the mantle is magnesium oxide. Other mantle elements include iron,
aluminum, calcium, sodium, and potassium.
 The temperature of the mantle varies greatly, from 1000° Celsius (1832° Fahrenheit)
near its boundary with the crust, to 3700° Celsius (6692° Fahrenheit) near its
boundary with the core. In the mantle, heat and pressure generally increase with
depth.
 The viscosity of the mantle also varies greatly. It is mostly solid rock, but less
viscous at tectonic plate boundaries and mantle plumes. Mantle rocks there are soft
and able to move plastically (over the course of millions of years) at great depth and
pressure.
 The Earth's mantle plays an important role in the evolution of the crust and provides
the thermal and mechanical driving forces for plate tectonics. The mantle is also the
graveyard for descending lithospheric slabs, and the fate of these slabs in the
mantle is a subject of ongoing discussion and controversy. Because subducted
plates are relatively cool, they decrease the temperature of nearby mantle, leaving
relatively warm mantle in the regions between two subduction zones. These broad,
warm regions of mantle, known as “mantle upwellings” are relatively buoyant and
rise, providing the return flow.

3. Outer Core

 Only layer of the Earth that is liquid, which is made up of molten nickel and iron
 is responsible for Earth's magnetic field. As Earth spins on its axis, the iron inside
the liquid outer core moves around.
 The Outer Core is about 3700-4300 degrees Celsius. The Inner Core is so hot it
causes all the metal in the Outer Core to melt into liquid magma.
 The Outer Core is about 2270 km thick. It is the second largest layer and made
entirely out of liquid magma.

4. Inner Core

 The Inner Core is the final layer of the Earth. It is a solid ball made of metal.

3
 The Inner Core is about 1250 km thick and is the second smallest layer of the Earth.
Although it is one of the smallest, the Inner Core is also the hottest layer.
 Is a solid ball composed of an element named NiFe. Ni for Nickel and Fe for Ferrum
also known as Iron.
 The Inner Core is about 5000-6000 degrees Celsius. It melts all metal ores in the
Outer Core causing it to turn into liquid magma.
o Lithosphere
 is composed of both the crust and the portion of the upper mantle that
behaves as a brittle, rigid solid.
o Asthenosphere
 Below the lithosphere is the asthenosphere is partially molten upper
mantle material that behaves plastically and can flow. The
asthenosphere can deform and reshape driven by heat energy which
circulate the convection current. Convection currents are flowing fluid
that is moving because there is a temperature or density difference
within the material.

Interfaces mark the boundaries between layers of Earth

 Mohorovičić discontinuity or Mo·ho [moh-haw-roh-vuh-chich, -hoh- or moh-hoh]

o the discontinuity between the crust and the mantle of the earth, occurring at
depths that average about 22 miles (35 km) beneath the continents and about
6 miles (10 km) beneath the ocean floor.

4
 Gutenberg Discontinuity
o The core–mantle boundary of the Earth lies between the planet's silicate
mantle and its liquid iron-nickel outer core. This boundary is located at
approximately 2891 km (1796 mi) depth beneath the Earth's surface.
 Lehmann discontinuity
o occurs between Earth’s inner and outer core at a depth of roughly 5,100 km
(about 3,200 miles).

3.1. Two Very Different Types of Crust

5
Oceanic Crust

 The crust that underlies the ocean floor

 Has an average thickness of 5 kilometers
 Composed of dense basaltic rocks made up of magnesium silicates

Continental Crust

 The crust that makes up the continents

 Is about 40-70 km thick
 Made up of light granitic rocks which made up of mostly aluminum silicates

4. Lesson 2 – Mapping the Inner Earth

How does scientist able to map the interior of Earth if they not visited its inner, deeper
layers? Scientist inferred the different layers of Earth by analyzing seismic waves
created by earthquakes, volcanic eruptions, and other tectonic processes which allow
them to learn the composition, density, and other properties of Earth’s layer.

Seismometer

 is an instrument that responds to ground motions, such as caused by

earthquakes, volcanic eruptions, and explosions. Seismometers are usually
combined with a timing device and a recording device to form a seismograph.

Seismograph

 An instrument that makes a record of seismic waves caused by an earthquake,

explosion, or other Earth-shaking phenomenon.

6
  equipped with electromagnetic sensors that translate ground motions into
electrical changes, which are processed and recorded by the instruments’ analog
or digital circuits.

The terms seismograph and seismometer are often used interchangeably; however,
whereas both devices may detect and measure seismic waves, only a seismograph
possesses the capacity to record the phenomena. A record produced by a seismograph
on a display screen or paper printout is called a seismogram.

Seismic Waves

 the shockwaves of released energy that shake the Earth and temporarily turn soft
deposits, such as clay, into jelly (liquefaction)
 from the Greek ‘seismos’ meaning ‘earthquake’
 are usually generated by movements of the Earth’s tectonic plates but may also
be caused by explosions, volcanoes and landslides.
 Detected by seismometers and recorded by a seismograph

Seismic waves are divided into two types: Body Waves and Surface Waves.

I. Body waves include P (compressional or primary) waves and S (transverse or

secondary) waves. An earthquake radiates P and S waves in all directions and the
interaction of the P and S waves with the Earth's surface and shallow structure
produces surface waves.

1 Primary waves (P Waves)

 are first to be felt on the Earth’s surface
 they travel at the speeds between 1.5 to 1.8 kilometers per second
 they shake the ground back and forth in the same direction the wave is moving
 pass through solid and liquid sections of Earth but refract or bend as they pass
through liquids
2 Secondary waves
 are felt in an up-and-down motion perpendicular to the direction of the wave
 Do not travel through liquids (the outer core was discovered to be liquid using
this principle)
 They travel about 60-70 percent more slowly than the P waves
 At farther distances the amplitude of the seismic waves decreases as the energy
released by the earthquake spreads throughout a larger volume of Earth.

7
Also, with increasing distance from the earthquake, the waves are separated apart in
time and dispersed because P, S, and surface waves travel at different speeds.

II. Surface waves. Near an earthquake the shaking is large and dominated by shear-
waves and short-period surface waves. These are the waves that do the most damage
to our buildings, highways, etc.

1. Love waves are transverse waves that vibrate the ground in the horizontal direction
perpendicular to the direction that the waves are travelling. They are recorded on
seismometers that measure the horizontal ground motion.
2. Rayleigh waves are the slowest of all the seismic wave types and in some ways the
most complicated. Like Love waves they are dispersive so the particular speed at
which they travel depends on the wave period and the near-surface geologic
structure, and they also decrease in amplitude with depth. Typical speeds for
Rayleigh waves are on the order of 1 to 5 km/s.

5. Lesson 3 – Plate Tectonics

Earth may appear as a solid, steady, and unchanging sphere of rock but in truth, it is
constantly undergoing minor or major changes externally and internally. Several
theories have been proposed to explain changes such as the formation of different

8
landforms, separation of continents, formation of new ocean floor, and movement of the
lithosphere plates. About 300 million years ago, Earth didn't have seven continents, but
instead one massive supercontinent called Pangaea, which was surrounded by a single
ocean called Panthalassa. The explanation for Pangaea's formation ushered in the
modern theory of plate tectonics, which posits that the Earth's outer shell is broken up
into several plates that slide over Earth's rocky shell, the mantle. Over the course of the
planet's 3.5-billion-year history, several supercontinents have formed and broken up, a
result of churning and circulation in the Earth's mantle, which makes up most of planet's
volume. This breakup and formation of supercontinents has dramatically altered the
planet's history.

9
The contraction theory early 20th century

 The earth started out as a molten blob and gradually cooled.

 As it cooled, heavier metals (Fe) sank down and formed the core, while lighter
metals (Al) stayed up in the crust.
 Pressure produced by contraction caused some parts of the crust to buckle
upwards, forming mountains.
 Other parts buckled downwards, creating ocean basins.

10
  Picture in your mind a grape turning into raisin as it dries out.

Continental drift Theory

The contraction theory was superseded by the theory of continental drift given by Alfred
Wegener which explains how the continents shifted and moved over time. He
propounded the idea that all the continents earlier formed a single landmass and later
on shifted their position (as they are at present). He called that supercontinent
(single/giant landmass) Pangea which was surrounded by the super ocean
Panthalassa.

Pangea later broke into two new continents i.e., Laurasia and Gondwana. Or...Pangea = Laurasia +
Gondwana and Earth = Pangea and Panthalassa

Evidence supporting the continental drift theory:

11
 Continent shape - they seemed to fit together

Fossil evidence - fossils of the same plants and animals were found on different
continents

12
Rock formations - found nearly identical on east coast of America and west coast of
Europe.

Climate clues - glacial deposits found in current warm climates and warm climate
plants fossils found in Artic.

13
Wegener didn't find evidence to explain the movement of the continents and his theory
was rejected. Half a century later, Wegener 's theory was finally accepted due to
advance in technology that improved our knowledge of earth's interior, the ocean floor
and the distribution of earthquakes and volcanoes. But today, this theory has been
replaced by the science of Plate Tectonics.

Seafloor Spreading Theory

Proposed by Harry Hess in the 1960s, which states that the seafloors or ocean floors –
not the continents – move and carry the continents along.

Process of Seafloor Spreading

 In the process of seafloor spreading, new ocean floor forms along earth’s mid-ocean
ridges, slowly moves outward across ocean basins, and finally sinks back onto the
mantle beneath deep-ocean trenches.
 During sea-floor spreading, new oceanic lithosphere is formed, and the ocean floor
gets wider.
 Today, the Atlantic Ocean is thousands of kilometers wide. Millions of years ago, the
Atlantic would have been a much narrower sea.

Theory of Plate Tectonics

When the concept of seafloor spreading came along, scientists recognized that it was
the mechanism to explain how continents could move around Earth’s surface. Like the
scientists before us, we will now merge the ideas of continental drift and seafloor
spreading into the theory of plate tectonics.

14
Seafloor and continents move around on Earth’s surface, but what is actually moving?
What portion of the Earth makes up the “plates” in plate tectonics? This question was
also answered because of technology developed during war times – in this case, the
Cold War. The plates are made up of the lithosphere.

Earthquake epicenters outline the plates. Mid-ocean ridges, trenches, and large faults
mark the edges of the plates, and this is where earthquakes occur.

The lithosphere is divided into a dozen major and several minor plates (figure 2). The
plates’ edges can be drawn by connecting the dots that mark earthquakes’ epicenters.
A single plate can be made of all oceanic lithosphere or all continental lithosphere, but
nearly all plates are made of a combination of both.

Movement of the plates over Earth’s surface is termed plate tectonics. Plates move at a
rate of a few centimeters a year, about the same rate fingernails grow.

How Plates Move

15
If seafloor spreading drives the plates, what drives seafloor spreading? Picture two
convection cells side-by-side in the mantle, similar to the illustration.

1. Hot mantle from the two adjacent cells rises at the ridge axis, creating new ocean
crust.
2. The top limb of the convection cell moves horizontally away from the ridge crest, as
does the new seafloor.
3. The outer limbs of the convection cells plunge down into the deeper mantle,
dragging oceanic crust as well. This takes place at the deep-sea trenches.
4. The material sinks to the core and moves horizontally.
5. The material heats up and reaches the zone where it rises again.

At present, there are 15 major tectonic plates that consist of seven primary plates and
eight secondary smaller plates. The primary plates are the Eurasian Plate, Australian
Plate, Pacific Plate, North American Plate, South American Plate, African Plate. The
secondary plates are Juan de Fuca Plate, Nazca Plate, Cocos Plate, Carribean Plate,
Philippine Sea Plate, Arabian Plate, Indian Plate, and Scotia Plate. Figure 2. Shows
these major plates.

6. Lesson 4 – Mechanism of Plate Movements

According to the theory of plate tectonics, the plates on Earth’s crust continually move,
although the speed at which they do so is so small – 2.5 cm per year. The movement of
plates is influenced by two types of forces: driving forces and resisting forces.

16
Driving forces either push tectonic plates toward one another or pull them apart.

 Mantle convection is caused by the rising of heat from the core toward the
mantle. Convection currents drive the plates away from one another. This heat
dissipates and creates a convection current due to the difference in temperature
between the mantle and the layer above it.
 Slab pull takes place when a subducting slab sinks into the hot mantle because
of a difference in temperature. The rest of the plate to which the slab is attached
to is pulled in as well.
 Slab suction occurs between two colliding plates, one subducting underneath
the other, whereby convection currents in the upper mantle suck both plates
down.
 Ridge push occurs when the lithosphere is pushed up by the asthenosphere
because of convection currents from the mantle. Gravity pushes the plate down
the ridge and a new crust is formed.

Resisting forces act against the driving forces of plate tectonics. They include the
following:

 Slab resistance is the force that resists all the forces associated with plate
movement in subduction zones.
 Collisional resistance occurs when a heavy plate is pulled into the mantle but
resists subduction because of friction. This force opposes the slab pull.
 Transform fault resistance is the frictional force due to the opposing movement
of plates moving past one another between two spreading centers.
 Drag force resists movement of lithospheric plates.

17
7. Quiz

___1. Good evidence that the density of the Earth increases gradually within a layer is
where seismic waves:

a. travel in gently curving paths due to refraction

b. suddenly changes paths when the density abruptly changes

c. travel in gently curving paths due to total internal reflection

d. travel in gently curving paths due to diffraction

e. travel in straight lines through the Earth

___2. One piece of evidence for Pangaea was that

a. Part of an organism was found on one landmass and the other part on another
landmass

b. A land bridge was found

c. The same fossilized organism was found on two different continents

d. People are found on all landmasses

___3. What usually causes tsunamis?

a. high-pressure weather systems

b. the collision of ocean currents

c. hurricanes

d. undersea earthquakes

___4. What two specific continents fit together most noticeably?

a. Antarctica and Africa

b. South America and Africa

c. South America and Europe

d. Africa and North America

___5. The interface between the mantle and the outer core is called the:

a. Mohorovicic discontinuity

b. asthenosphere

18
c. Gutenberg discontinuity

d. lithosphere

___6. Which is the thickest layer of Earth?

a. lithosphere

b. crust

c. core

d. mantle

___7. What causes Earthquakes?

a. The flow of magma

b. The contraction of the Earth's crust

c. The expansion of the Earth’s crust

d. The Earth’s plates rubbing together

e. The explosion of volcanoes

8. Match the following theories with their brief discussion.

a. Earth’s lithosphere is composed of slabs of solid rocks, which float on an inner

pliable mantle.
b. There once a single landmass or supercontinent existed.
c. As Earth cooled, its surface wrinkled and these wrinkles being the mountain range
on Earth’s surface.
d. The ocean floors move and carry the continents along.

___ Plate Tectonics

___ Contraction Theory

___ Seafloor Spreading

___ Continental Drift Theory

___9. S waves can travel through

a. Neither solid or liquid

b. Both liquids and solids

c. Liquids but not solids

d. Solids but not liquids

19
___10. The only liquid layer of Earth is the:

a. mantle b. inner core c. core d. outer core

__________11 (True or False). The outermost layer of the Earth where life exists is
called the crust.

___12. A break in the Earth's crust along which rocks move is called:

a. an epicenter b. a volcano c. an earthquake d. a fault

___13. The Earth’s core is best described like this:

a. It is a thin layer of rock

b. It is just over half of the Earth's diameter, the outer part of which is liquid and the
inner part of which is solid

c. It is extremely viscous - density decreases with depth and which extends almost
halfway to the center of the Earth

d. It is extremely viscous. Its density increases with depth which extends almost halfway
to the center of the Earth

e. It is just over half of the Earth's diameter, the outer part of which is solid and the inner
part of which is liquid

___14. Which layer of the earth is a solid and why?

a. The inner core is solid because of the high pressure that drop the temperature inside
the core.

b. The inner core is solid because of the low pressure and below freezing temperatures.

c. The inner core is solid because of a balance between hot and cold temperatures.

d. The inner core is solid because of the sky-high pressure and temperatures.

e. The inner core is solid because of the movement of the outer core.

___15. Wegener's hypothesis was:

a. That the landmasses had been joined together as Pangaea, and have since drifted
apart

b. That the landmasses have always been in the same places

c. That earthquakes have caused the landmasses to move

d. That the continents do not move

___16. How do scientists know what the mantle and core are like?

20
a. Seismic waves

b. Direct observation

c. On-site research trips

d. Robotic equipment

___17. The Earth’s crust is best described like this:

a. It is just over half of the Earth's diameter, the outer part of which is solid and the inner
part of which is liquid

b. It is a thin layer of rock

c. It is just over half of the Earth's diameter, the outer part of which is liquid and the
inner part of which is solid

d. It is extremely viscous. Its density increases with depth which extends almost halfway
to the center of the Earth

e. It is extremely viscous - density decreases with depth and which extends almost
halfway to the center of the Earth

___18. Which is not a driving force that influence the movement of tectonic plates?

a. slab push b. drag force c. ridge push d. mantle convection

___19. Who is the scientist credited for establishing the foundation for the theory of
plate tectonics?

a. Alfred Wegener

b. John William Strutt

c. Andrija Mohorovicic

d. Augustus Edward Love

___20. When resisting force of plate movement opposes the slab pull?

a. slab resistance

b. collisional resistance

c. transform fault resistance

d. drag force

___21. What is the densest layer of the earth?

a. Mantle b. Inner Core c. Crust d. Outer Core

21
___22. Some volcanoes form new ______ as plates move apart and magma rises to
the surface of the crust.

a. Ocean floor b. Volcanoes c. Earthquakes d. Mantle

___23. Which layers make up the asthenosphere?

a. Only the crust

b. The asthenosphere does not exist

c. Bottom part of the upper mantle

d. Crust, mantle, and core

e. Crust, and uppermost part of the mantle

___24. The Earth’s mantle is best described like this:

a. It is just over half of the Earth's diameter, the outer part of which is solid and the inner
part of which is liquid

b. It is extremely viscous. Its density increases with depth which extends almost halfway
to the center of the Earth

c. It is extremely viscous - density decreases with depth and which extends almost
halfway to the center of the Earth

d. It is a thin layer of rock

e. It is just over half of the Earth's diameter, the outer part of which is liquid and the
inner part of which is solid

___25. No one believed Wegener because:

a. He did not give any evidence

b. He did not provide an explanation for the force that moved the continents

c. He was not well liked by people

d. His ideas were false

___26. What are seismic waves caused by?

a. Thunder b. Traffic c. Earthquakes d. Volcanoes

___27. The Mohorovicic discontinuity was discovered by the studying the behavior of:

a. fossil sequences b. seismic waves c. coastal lines d. rock formation

___28. Which layers make up the lithosphere?

22
a. Crust, mantle, and core

b. The lithosphere does not exist.

c. Crust and uppermost part of the mantle

d. Only the crust

e. Bottom part of the upper mantle

___29. An underground holding pool for hot magma is called a:

a. Magma chamber

b. Crater

c. Fault

d. Vent

___30. How does the energy of an earthquake travel through the Earth?

a. Seismic waves carry the energy of an earthquake away from the focus, through the
Earth's interior, and across the surface.

b. Seismic waves carry the energy of an earthquake toward the focus, through the
Earth's interior, and across the surface.

c. During an earthquake, seismic waves move toward the focus and epicenter then
move out in all directions.

___31. P waves are:

a. Transverse

b. Longitudinal

c. Ultrasonic

d. Electromagnetic

___32. Choose the correct statement:

a. It is not possible to record the speed of S and P waves

b. S waves are slower than P waves

c. P waves are slower than S waves

d. P waves have the same speed as S waves

23
8. Assignment

Kindly follow the instructions. Use bond paper or notebook to write your answer and
take a picture of your work. You can also answer digitally and submit the file.

1. In one whole short bond paper, draw and label the different layers of the earth

2. In a paragraph using your own words, describe each layer in terms of state of matter,
composition, thickness, and temperature

3. Using your own words differentiate the following:

a. lithosphere and asthenosphere

b. P waves and S waves
c. Mohorovicic discontinuity and Gutenberg discontinuity

4. Answer the question briefly using your own words. Question: HOW DID SCIENTIST
LEARN ABOUT THE STRUCTURE OF INNER EARTH?

9. Forum

To be announced by your subject adviser.

10. Enrichment Activity

Please see the next page.

24
25
26
27