Earth’s Interior Notes
92 – Heat from Earth’s interior is the major source of energy for the movement of
Earth’s outer shell.
93 – Scientists have determined that Earth’s interior is divided into four major
layers.
94 - At Earth’s center is the inner core, a solid, iron-rich sphere having a diameter
of 2432 kilometers (1511 miles).
95 – Surrounding the inner core is the outer core, a fluid, metallic layer some
2270 kilometers (1410 miles) thick.
96 – Beyond the outer core is the mantle, a solid, rocky layer having a thickness
of about 2885 kilometers (1789 miles).
97 – Over 82% of Earth’s volume is contained within the mantle, a thick shell of
rock composed of silicate minerals that are rich in iron and magnesium.
98 – The outermost layer is the crust, a very thin outer skin that ranges from
about 7 to more than 70 kilometers (5 to 40 miles) thick.
99 - Earth’s crust is further divided into continental crust and oceanic crust.
100 – In most regions, the continental crust is about 35 km (20 miles) thick, but it
may exceed 70 km (40 miles) in areas of prominent mountains.
101 – The continental crust consists of many types of rocks. One of the most
common in the upper crust is the igneous rock granite.
102 – Compared to continental crust, oceanic crust is quite thin, averaging only 7
km (5 miles) in thickness.
103 – In addition, the oceanic crust is very uniform in composition, being mainly
composed of the dark igneous rock basalt.
104 – On average, continental rocks are less dense (weigh less in equal
amounts) than oceanic rocks, which partially explains the lower position of the
ocean floor compared to the continents.
105 – In addition to Earth’s four major layers, scientists have identified two other
divisions of Earth’s interior – the asthenosphere and the lithosphere.
106 – The asthenosphere is located within the upper mantle, between the
depths of 100 to 660 km…
107 – … and is composed of hot, rocky material that is capable of very slow
movement.
108 – Situated above the asthenosphere is a zone called the lithosphere.
109 – The lithosphere includes the uppermost mantle and overlying crust and
behaves as a strong, rigid layer.
110 – In contrast to the hot, weak zone below, the lithosphere is strong because
it is composed of comparatively cool rocks.
111 – Geologists have discovered that the weak rock within the asthenosphere
allows earth’s rigid outer shell (lithosphere) to move.