60 The History of the Earth: Supplemental Guide 3A | The Earth Inside-Out, Part II
Presenting the Read-Aloud 15 minutes
The Earth Inside-Out, Part II
Show image 3A-1: Diagram of the layers of the earth^1
Today, we are going to pretend that we can journey deep, deep
into the earth, all the way to the very center, nearly four thousand
miles from where you are sitting right now.
The fi rst stop is the layer beneath the crust, which is called the
mantle. The mantle is a whopping 1,800 miles thick and contains
most of the earth’s rock.^2 Because most of the earth is made of
rock, that means that most of the earth is contained within the
mantle.
The mantle is mostly made of solid rock. The closer to the
crust, the cooler and harder the mantle tends to be. But as you go
deeper, closer to the core, the mantle gets hotter and becomes
soft and gooey. Heat closer to the core causes the rock inside the
mantle to move around quite a bit. But in most places, it is still
solid rather than liquid. 3
The mantle surrounds the core, or center, of the earth. The core
has two parts: the inner core and the outer core. The inner core
is a solid metal ball.^4 The outer core is also metal, but it is not
solid—it is made up of melted, or molten, metal.^5 This means that
deep down inside the earth—thousands of miles beneath your
feet—there is a giant sea of red-hot, molten metal surrounding a
solid metal ball.
Scientists believe that the very center of the earth—the inner
core—is actually hotter than the surface of the sun, which is a
blazing 10,000 °F!^6 The inner core is much hotter than the outer
core. It may seem strange, therefore, that the outer core of the
earth is molten metal, yet the inner core—at the very center of the
earth where it is hottest—is a solid ball of metal, which by the way
is just a bit smaller than the moon!1 [Point to the layers in the diagram
as they are named in the read-
aloud.]
2 [Show students the distance from
New York to Colorado on a map,
and tell them that it is roughly the
thickness of the mantle.]
3 Did you hear the word heat again?
Heat causes parts of the mantle to
move around. Remember, solids
keep their shape, while liquids
move around and can be poured.
4 What does it mean if the inner core
is solid?
5 If metal is molten, heat has
changed it from solid to liquid.
6 A really hot day in the United
States is about 100 °F, so 10,000 °F
is extremely hot! [Write out the
two numbers so that students can
see just how much bigger 10,000
is.]