Grade 1 - A History Of The Earth

The History of the Earth: Supplemental Guide 3A | The Earth Inside-Out, Part II 61

The reason that the inner core is solid has to do with the

incredible pressure of the earth’s entire weight pressing inward.

The more pressure you put on something, the more heat you

need to cause that thing to boil or melt. This is why the metal at

the very center of the earth—the inner core—is solid instead of

liquid. Despite the intense heat, there is simply too much pressure

caused by the weight of the rest of the earth, so the center of the

earth cannot melt, and it remains solid.^7

 Show image 3A-2: San Bernardino Mountains

The crust upon which we live is constantly being changed

and reshaped due to heat and pressure caused by activity in the

earth’s mantle and core. The San Bernardino Mountains that you

see in this picture, along with many other mountains along the

West Coast of the United States, from Mexico to Alaska, were

created by changes inside the earth.

 Show image 3A-3: Diagram of a volcano

Remember, the parts of the mantle that are closest to the core

are soft and gooey. That hot, gooey material in the mantle does

not always stay in the mantle. Sometimes it rises up to the surface.

Every so often, some of that extremely hot molten rock, or magma,

pushes up through the mantle and forces its way into cracks and

crevices in the crust.

Over time, the magma collects in a magma chamber, such as

the one near the bottom of the picture. The heat in the magma

chamber releases gas from the magma, which builds up and

creates pressure. The pressure builds and builds until... one

day ... BOOM!^8 The magma erupts in a volcano of lava, ash, gas,

and fi re. Once it is released from the earth, the magma becomes

lava—fl owing liquid rock, which fl ows across the ground until it

cools and hardens into rock once again.^9

7 Did you hear the word pressure
again? Pressure causes the inner
core to be solid rather than liquid.

8 Did you hear the words heat and
pressure again? Heat and pressure
cause volcanoes to erupt.

9 The eruption of lava, ash, gas, and
fi re forms a mountain called a
volcano.