lithosphere The solid layer of Earth, made of rock.
magnetic field A region of space surrounding an object, in which an attractive magnetic
force can be detected.
orbit The path of an object, such as a planet or moon, around a larger object such as the
Sun.
sphere An object similar in shape to a ball.
Points to Consider
- What would other planets need to have if they were able to support life?
- Would life on Earth be impacted if Earth lost its magnetic field?
- Could a large gas planet like Jupiter or Saturn support life?
24.2 Earth’s Motions
Lesson Objectives
- Describe Earth’s rotation on its axis.
- Describe Earth’s revolution around the Sun.
Introduction
Imagine a line passing through the center of Earth that goes through both the North Pole
and the South Pole. This imaginary line is called anaxis. Earth spins around its axis, just
as a top spins around its spindle. This spinning movement is called Earth’srotation. At
the same time that the Earth spins on its axis, it also orbits, or revolves around the Sun.
This movement is calledrevolution.
Earth’s Rotation
In 1851, a French scientist named Léon Foucault took an iron sphere and swung it from a
wire. He pulled the sphere to one side and then released it, letting it swing back and forth in
a straight line. A ball swinging back and forth on a string is called a pendulum. A pendulum
set in motion, will not change its motion, so it will not change the direction of the swinging.
However, Foucault observed that his pendulum did seem to change direction. He knew that