5 5 4 earth the inside story

The Plutonists believed that Earth’s surface rested on a mass of molten rock, and they pointed to Earth’s volcanoes as proof.. They said that if Earth’s crust floated on water, then volc

Suggested levels for Guided Reading, DRA,

Lexile, ® and Reading Recovery ™ are provided

in the Pearson Scott Foresman Leveling Guide.

ISBN 0-328-13571-2

ì<(sk$m)=bdfhbe< +^-Ä-U-Ä-U

Genre Comprehension

Skills and Strategy Text Features Expository

nonfi ction

• Cause and Effect

• Fact and Opinion

• Summarize

• Captions

• Diagrams

• Time Line

• Glossary

Scott Foresman Reading Street 5.5.4

Earth Science

Earth:

The Inside Story

by Camilla Calamandrei

Suggested levels for Guided Reading, DRA,

Lexile, ® and Reading Recovery ™ are provided

in the Pearson Scott Foresman Leveling Guide.

ISBN 0-328-13571-2

ì<(sk$m)=bdfhbe< +^-Ä-U-Ä-U

Genre Comprehension

Skills and Strategy Text Features Expository

nonfi ction

• Cause and Effect

• Fact and Opinion

• Summarize

• Captions

• Diagrams

• Time Line

• Glossary

Scott Foresman Reading Street 5.5.4

Earth Science

Earth:

The Inside Story

by Camilla Calamandrei

Reader Response

1 What caused people to question whether Earth was

solid? What effect did the discovery of undersea mountain ridges have? Use a graphic organizer like this one to record two more cause-effect relationships discussed in the book

2 In your own opinion, which scientist or scholar

featured in the book is most interesting and why?

3 The term “Continental Drift” is not defined in the

book What do you think it means? How did you figure that out?

4 Think about the volcanoes and earthquakes described

in this book How do you think scientists should use what they learn about Earth to help people?

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Earth:

The Inside Story

by Camilla Calamandrei

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2 3 4 5 6 7 8 9 10 V0G1 14 13 12 11 10 09 08 07 06 05

Today, we understand a great deal about volcanoes, earthquakes, and tidal waves, and we understand how they are related.

3

The Earth in Motion

Earth may look like a calm planet when viewed from outer space But it is anything but calm In fact,

we live on a planet that is constantly moving and changing

Earth moves in a few different ways First of all,

we now know that Earth revolves around the sun

We also know that it spins on an axis But the planet itself is not one solid piece of rock Different layers of Earth itself are moving and changing all the time

Earthquakes, volcanic eruptions, and tidal waves

are all dramatic side effects of layers of the planet

moving into and away from each other They remind

us that things are always happening within the

planet

Read on to find out how scientists learned that

Earth is made of layers

Pieces of a Puzzle

For thousands of years, humans thought

Earth was a solid mass Even the famous Greek

philosopher Aristotle, who lived more than 2,300

years ago correctly thought Earth was round, long

before others realized it But he thought, incorrectly,

that Earth was solid

It was not until 2,000 years later that some

evidence came to light that made a few people

begin to question whether the Earth really was solid

Before the invention of the airplane, maps were

challenging to make Early mapmakers had to

reconstruct entire coastlines on paper, even though

they could see and measure only the small area

that was in front of them at any given moment

Today, our maps are very precise because planes and

satellites allow us to see Earth’s landmasses—and

many miles of coastline—from above

An early map of the world

5

During the 16th century, explorers sailing the seas in search of new routes from Europe to the East came upon continents they had not known about

Each of these expeditions included mapmakers

These mid-16th century maps revealed something amazing It appeared that the western edge of the African continent and the eastern edge of the South American continent could fit together like two pieces

of a jigsaw puzzle Could that really have happened

by chance?

African continent

South American

continent

The English philosopher Francis Bacon (1561–

1626) believed that the interlocking shapes of the coastlines of Africa and South America did not happen by chance Other scholars and scientists felt the same way Some philosophers believed that Africa and South America had once been a single, large landmass

They were less certain, however, about what had caused the landmass to split They did not know how

or why the continents floated so far from each other

How could such a thing happen if Earth were solid all the way through?

Some people decided that the waters of a great flood—described in the Bible—had divided the original continent and floated its parts to different hemispheres The idea that the flood had changed Earth’s surface became popular Francis Bacon even went along with it

If Earth were solid, though, as people believed, then where did the water for such a huge flood come from? Some scientists and scholars decided that Earth’s entire surface must float on water They speculated that chemicals in the water had somehow dissolved the solid core of Earth and caused it to break apart

Neptune, Roman God of the Sea

Pluto, Roman God of the Underworld

The idea that the continents floated on water

became known as the Neptunist idea It was named

for the Roman god of the sea and earthquakes,

Neptune

A competing idea that emerged in the late 1700s

was called the Plutonist idea Pluto was the god of

the underworld The Plutonists believed that Earth’s

surface rested on a mass of molten rock, and they

pointed to Earth’s volcanoes as proof They said that

if Earth’s crust floated on water, then volcanoes

would spew water instead of molten lava

8

Solid core Liquid rock Earth’s crust

9

Three Layers

By the 1870s, most geologists (scientists who study Earth’s origin and structure) believed that Earth was

made up of three layers—a rigid crust that encases

Earth, a solid core, and liquid rock that surrounds Earth’s core

This basic description of the Earth’s interior was scientifically confirmed in the late 1800s and early 1900s Scientific developments in the mid-1900s allowed even greater, more complex, understanding

of the layers that make up the planet

During the mid-1800s, scientists seemed to have

put aside the question inspired by the maps of the

1500s: How could the continents have moved or

floated away from one another if Earth’s crust is a

rigid shell? They focused on the fact that there was

molten, or liquid, rock under the crust They called

this layer of liquid rock between Earth’s surface and

its core, the mantle, but they did not explain how

pieces of the crust could have moved

Geologists didn’t know whether the mantle was

all molten rock or if part of it might be solid They

also were eager to find proof that Earth had a solid

core, as they believed

A Solid Core

In 1880, English geologist John Milne and his

team invented the first accurate seismometer This

machine is used to locate earthquake shocks and

measure the strength of an earthquake A machine

called a seismograph is used to record earthquakes

Geologists using seismometers and seismographs

noticed that the shocks, or waves, of earthquakes

varied

During an earthquake, the frame of the seismograph shakes, but the weight with the pen attached stays still When the frame shakes, it moves the paper below the pen, which records the size of the shock waves Scientists use this record to calculate the earthquake’s strength.

Frame movement

How a Seismograph Works

Weight

Pen Paper Drum

Ground movement

11

Experts knew that the waves would have

measured the same if they were traveling through

the same kind of material The fact that the shock

waves varied told them that the waves were

traveling through different materials Geologists

began to study the measurements of these

waves for clues about what made up Earth’s

interior

The English seismologist Richard Dixon

Oldham performed studies in 1906 indicating

that Earth’s core was dense

In 1936, the Danish seismologist Inge

Lehmann documented that some seismic waves

during an earthquake did not travel through Earth’s

core but bounced back She concluded that Earth

has a central inner core that is solid iron and a

surrounding outer core that is made of liquid iron

It is now known that the inner core is a solid iron

ball approximately the size of the moon It can reach

temperatures from 6,700º to 12,600º Fahrenheit

(possibly more) The intense heat of the inner core

keeps the outer core in a permanently molten state

At the same time, the pressure from the outer core

keeps the inner core solid

Inner core

Outer core

13

The pressure and temperature of the earth increases as one

moves closer to the center.

Inner core

about 6,700°F–12,600°F

Outer core

about 8,000°F–11,000°F

Crust Mantle

about 1,600°F

14

This is how the continents may have looked millions of years ago

15

Continental Drift

In 1912, the German scientist Alfred Wegener suggested that Africa and South America had once been one continent As you know, he was not the first to have this idea (remember the maps of the 1500s), but he did offer new thinking on the subject

Wegener noticed two things in his research First,

fossils of similar extinct plants had been discovered

in both Africa and South America This suggested that at the time the fossils were living plants, the two continents had been one Second, modern, more detailed maps showed that other continents besides South America and Africa had coastlines that seemed

to interlock This suggested that other continents may once have been connected as well

After gathering more clues, Wegener decided

that all of the continents had once been one

super-continent He suggested that approximately

200 million years ago, this super-continent (or

Pangaea, as he called it) had split, and its fragments

had gradually drifted apart He also claimed the

continents were still floating away from one another

Because most geologists in 1912 still thought

that Earth’s surface was an unbroken shell, they

were unsure of Wegener’s idea Wegener died while

conducting research in Greenland in 1930 Though

his work still had not been widely accepted, soon it

would be

In the 1950s, important information about Earth’s

crust came to light A group of scientists exploring

the ocean floor discovered a long chain of ridges

that formed an underwater mountain range As

they examined these ridges, they realized that these

undersea mountains had developed along a deep

crack in Earth’s crust This proved that Earth’s crust is

not an unbroken shell

Just as the philosopher Aristotle had been right that Earth was round but wrong that it was solid, Francis Bacon was right about one thing but wrong about another

Alfred Wegener’s research in the 1900s showed that Bacon was right in the 1500s when

he proposed that Africa and South America had once been one continent The discovery that Earth’s crust floats on molten rock proved that Bacon was wrong in thinking that the continents float on water

Francis Bacon

Alfred Wegener

17

By 1960, it was understood that the crust of Earth

is rigid, but it is not one solid piece like a layer of

armor Instead, Earth’s crust is broken into separate

pieces that scientists call tectonic plates These plates float on the layer of molten rock below the crust’s surface

The molten rock moves, and it carries the tectonic plates to different locations This explains how the continents moved in the past and introduces the idea that they are still moving

1500s Maps show that African

and South American coastlines

appear to interlock Philosopher

Francis Bacon (1561–1626) proposes

that Africa and South America must

have once been one continent.

1890

1880

1880 Geologist John Milne invents the modern seismograph.

18

Once they accepted Wegener’s theory that Earth’s

crust is not an unbroken shell, geologists began to

piece together the history of Earth’s continents

It is now believed that 225 million years ago,

Earth had one great landmass (Pangaea), as Wegener

had proposed Then, about 200 million years ago,

Pangaea began to split apart, and there were two

great landmasses The southern landmass included

the land that would become South America, Africa,

India, Australia, and Antarctica The northern

landmass included the land that would become all of

Asia (except India), Europe, and North America

Scientists believe that about 135 million years

ago the two landmasses started to break into the

continents that we know today

P A

N

G

A

Northern landmass (Laurasia) and Southern landmass (Gondwanaland) 200 million years ago

1960

L A U R A S I A

G O N D W

A N

A LA N D

Pangaea 225 million years ago

1930

1906 Seismologist Richard Dixon Oldham shows that Earth’s core is dense

1936 Seismologist Inge Lehmann documents that Earth’s core is solid.

1950s Scientists exploring the ocean floor prove that Earth’s crust is not an unbroken shell.

1960s Plate Tectonic Theory

is introduced.

1912–1930 Scientist Alfred Wegener introduces the concept

of continental drift.

19

Plate Tectonics

The more scientists learn about Earth’s inner

structure, the more they understand how events

occurring in the interior of the planet actually shape

the surface of the planet

You may have heard people talk about old

mountains versus new mountains Or perhaps you

know that some volcanoes spew lava and other

volcanoes produce a huge amount of ash during an

eruption You may have heard that earthquakes tend

to happen along something called a fault line All

of this is related to plate tectonics—how the plates

of the Earth move into one another, against one

another, away from one another, and so on

Plates form a fault or fault line where they meet

Fault lines can run over many miles in a rather

straight line, or they can curve a little like a serpent

The plates on either side of the fault move past each

other in different directions Usually, they move

slowly When they move quickly, an earthquake

occurs

21

When two plates collide, the plate edges can fold and produce mountains Also, when Earth’s crust

is squeezed together by tectonic plate movement, blocks of land may lift up between two faults and form mountains

Finally, a heavier plate and a lighter plate can meet and produce volcanic mountains The heavier plate sinks under the lighter plate, and the edge of

the heavier plate is plunged into the mantle of Earth

where the edge melts This molten rock then forces its way to the surface as a volcano In some cases, lava will flow out of a volcanic mountain and run down the sides for miles and miles

In other cases, huge amounts of ash will explode from the volcano and fill the sky This kind of

explosion can do hideous damage to animal and

plant life