24 The History of the Earth: Supplemental Guide 1A | Our Home, Earth
Show image 1A-7: Outer space
Some scientists believe the history of the earth begins a little
over four-and-a-half billion years ago. 4 That’s a long time—a very,
very, very long time—ago. Before that, some scientists believe the
materials that now make up Earth were orbiting, or fl oating around,
our newly formed sun as billions of little bits and pieces. Over
many, many years, it is believed by some scientists that these
fl oating bits and pieces gradually stuck together until they made
up Earth, as well as its neighbor, the moon, and the other planets.
When it was newly formed, Earth was basically one big ball of
hot, melted rocks. Over time, however, some of these materials
cooled and hardened, allowing the planet Earth to become what it
is today.
Show image 1A-8: Diagram of the solar system
Maybe you already know that Earth is a planet. Earth is one of
eight major planets that orbits the sun. 5 Do you know the names
of any of the other planets? 6 I do! Mercury, Venus, Mars, Jupiter,
Saturn, Uranus, and Neptune.
Like the other planets in the solar system, Earth is trapped
in the gravitational pull of the sun. This causes Earth to orbit, or
revolve, around the sun. It takes one year, about 365 days, for
Earth to complete an orbit around the sun.^7 Show image 1A-9: World map
The earth’s orbit around the sun is not the only way Earth
moves in space, however.
This map shows the earth’s north and south poles. 8 The north
and south poles are imaginary points at the northernmost and
southernmost parts of the earth. The axis of rotation is like an
imaginary line or “stick” going right through the earth at the north
and south poles. 9 There is not really a “stick” running through the
earth around which it turns. The axis is an imaginary line around
which earth rotates. The earth rotates, or spins, in the same way4 [Write the number four-and-a-half
billion (4,500,000,000) out for
students so that they can get a
sense of how long ago the earth’s
history began.] That’s a very, very,
very long time ago!
5 [Point to Earth on the diagram.]
Earth is the third planet from the
sun.
6 [Pause for responses and point out
each planet on the diagram.]
7 [Ask two students to demonstrate
by having one student be a
stationary sun and the other be the
orbiting Earth.]
8 [Point to the north and south poles
in the diagram.] Tell students there
is a star marking the North Pole
and a circle marking the South
Pole.
9 Here, the word stick means a long,
thin piece of wood. The word stick
also has other meanings. The
word stick also means to attach
something to a surface using glue
or tape, kind of like a sticker.