Earth’s Structure
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Chapter 1 Key Concepts
Lesson 1: The Earth System
What are the Main Parts of the Earth System?
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A system is a group of parts that work together as a whole.
The Earth system involves a constant flow of matter though different parts. The constant flow,
or cycling, of matter through the Earth system is driven by energy. Energy is the ability to do
work. The energy that drives the Earth system has two main sources: heat from the sun and
heat flowing out of Earth as it cools.
The Earth system has four main spheres: the atmosphere, the hydrosphere, the geosphere, and
the biosphere. As a major source of energy for Earth processes, the sun can be considered part
of the Earth system as well.
Earth’s atmosphere is the relatively thin envelope of gases that form Earth’s outermost layer.
Earth’s geosphere has three main parts: a metal core, a solid middle layer, and a rocky outer
layer. The hydrosphere contains all of Earth’s water. The part of Earth that contains living
organisms makes up the biosphere.
When feedback occurs, a system returns—or feeds back—to itself data about a change in the
system. Feedback demonstrates how changes in one part of the Earth system might affect the
other parts.
How do Constructive and Destructive Forces Change Earth?
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Lands are constantly being created and destroyed by competing forces.
Forces that construct, or build up, mountains are called constructive forces. Constructive forces
shape the land’s surface by building up mountains and other landmasses.
o Volcanoes build up Earth’s surface by spewing lava that hardens into rock.
o Earthquakes build landmasses by lifting up mountains and rock.
Because forces such as ice, rain, wind, and changing temperatures wear down, or destroy,
landmasses, they are called destructive forces. Destructive forces destroy and wear away
landmasses through processes like erosion and weathering. Erosion is the wearing down and
carrying away of land by natural forces such as water, ice, or wind.
Earth’s Structure
Lesson2: Convection and the Mantle
How Do Geologists Learn About Earth’s Interior?
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Geologists have used two main types of evidence to learn about Earth’s interior: direct evidence
from rock samples and indirect evidence from seismic waves.
Geologists have drilled holes as deep as 12.3 kilometers into Earth. The drills bring up samples of
rock. These rocks give geologists clues about Earth’s structure and conditions deep inside Earth.
When earthquakes occur, they produce seismic waves. Geologists record the seismic waves and
study how they travel through Earth.
What Are the Features of Earth’s Crust, Mantle, and Core?
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The three main layers of Earth are the crust, the mantle, and the core. These layers vary greatly
in size, composition, temperature, and pressure.
Pressure results from a force pressing on an area. The temperature and pressure inside Earth
increase with depth.
Earth’s crust is the layer of rock that forms Earth’s outer skin. The crust is a layer of solid rock
that includes both dry land and the ocean floor. The overall composition of oceanic crust is
much like basalt, a dark rock that has fine grains. Overall the composition of continental crust is
much like granite, a rock that usually is a light color and has coarse grains.
The solid material of the mantle is a layer of hot rock. Earth’s mantle is made of rock that is very
hot, but solid. Scientists divide the mantle into layers based on the physical characteristics of
those layers. Overall, the mantle is nearly 3,000 kilometers thick.
o Geologists often group the crust and uppermost mantle into a single layer called the
lithosphere. The soft layer just beneath the lithosphere is called the asthenosphere.
The core is made mostly of the metals iron and nickel. It consists of two parts—a liquid outer
core and a solid inner core. The outer core is a layer of molten metal surrounding the inner core.
The inner core is a dense ball of solid metal. Scientists think that movements in the liquid outer
core create Earth’s magnetic field.
Earth’s Structure
Lesson 3: Convection and the Mantle
How is Heat Transferred?
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Heat is constantly being transferred inside Earth and all around Earth’s surface. The movement
of energy from a warmer object to a cooler object is called heat transfer. There are three types
of heat transfer: radiation, convection, and conduction.
The transfer of energy that is carried in rays like light is called radiation. Heat transfer by the
movement of a fluid is called convection. Heat transfer between materials that are touching is
called conduction.
How does Convection Occur in Earth’s Mantle?
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Density is a measure of how much mass there is in a given volume of a substance. The flow that
transfers heat within a fluid is called a convection current.
Heating and cooling of a fluid, changes in the fluid’s density, and the force of gravity combine to
set convection currents in motion. Inside Earth, large amounts of heat are transferred by
convection currents within the core and mantle. Heat from the core and the mantle itself causes
convection currents in the mantle.
Over millions of years, the great heat and pressure in the mantle have caused solid mantle rock
to warm and flow very slowly. Many geologists think that plumes of mantle rock rise slowly from
the bottom of the mantle toward the top. The hot rock eventually cools and sinks back through
the mantle. Over and over, the cycle of rising and sinking takes place. Convections currents like
these have been moving inside Earth for more than four billion years!