26 The History of the Earth: Supplemental Guide 1A | Our Home, Earth
The second word is pressure, like the force you use when
you push on something. 14 Pressure, or the force of weight, also
causes many changes to the earth.
Time is the third important geology word to remember. To
understand geology, you need to think about time in a whole new
way. Forget about minutes, hours, and days. These amounts of
time don’t mean much in geology. Geologists think in terms of
many, many years. 15 It takes a long time for pressure and heat to
do what they do.
Show image 1A-12: Grand Canyon with view of Colorado River
The Grand Canyon, located in Arizona, provides a lot of clues
about the earth’s formation and history. It took millions of years for
the rushing water in the river to carve through the rocks to make
this canyon. No other place on earth allows me to see and study so
many different layers of rock at the same time. The rock on the upper
rim of the Grand Canyon is estimated by some scientists to be about
230 million years old, whereas the rock layers at the very bottom of
the canyon are estimated to have formed over two billion years ago.
That rock is half as old as the earth is believed to be itself!
Remember: heat, pressure, and time are the main factors of
geology. If you understand those three words, then you are ready to
move ahead and learn many things about the history of the earth. 16Discussing the Read-Aloud 15 minutes
Comprehension Questions 10 minutes
If students have diffi culty responding to questions, reread
pertinent passages of the read-aloud and/or refer to specifi c
images. If students give one-word answers and/or fail to use
read-aloud or domain vocabulary in their responses, acknowledge
correct responses by expanding students’ responses using richer
and more complex language. Ask students to answer in complete
sentences by having them restate the question in their responses.- Literal What does Gerry the Geologist study? (Gerry the
Geologist studies rocks to learn about the earth.)
15 Remember how long ago four-and-
a-half billion years was!
16 [Have students chant three times,
“Heat! Pressure! Time!”]
14 [Pause for students to push their
hands together using pressure.]