The Origin of the Moon
Background Information:
A theory in science is an explanation of why something occurs or behaves the way that it does in nature. In order for a theory explaining the
Moon’s formation to be accepted, it should account for everything we currently know about the Moon. The observations we can make about the
moon include:
 The Moon seems to be made of the same material as the Earth's upper mantle.
• The Moon has little or no iron in it, and is composed of material unlike the composition of the Earth as a whole.
• The Moon is rounded in shape, like the other planets and not like an asteroid or comet
• The Moon orbits in the same direction as the Earth
• The Moon is located in the same plane as the Earth (the ecliptic plane)
• Theory suggests that the Moon seems to have drifted away from the Earth over the length of geologic history.
• This means that the Moon was once much closer to the Earth
• This means that the Moon was once bigger in the sky and much brighter than at present.
Directions:
Your group will be assigned one of four theories regarding how the moon formed. It is up to your group to determine whether your assigned
theory of the moon’s origin is acceptable or not and why. In order to make this decision you will read about your assigned theory and determine
whether it accurately explains the observations of the Moon listed above.
You will create and present an informative handout to the class that includes the following information: description of your theory, evidence that
supports your theory, and evidence that does not support your theory. From this you will conclude whether or not we should accept your theory
as the one that best describes how the moon formed.
Presentation Notes:
Name of
Theory
Description of Theory
Co-Formation
Theory
Moon formed in orbit around
the Earth as the Earth formed.
Both the Moon and the Earth
were born in the Solar Nebula.
Capture
Theory
Moon formed somewhere else
in the Solar System.
The Moon then came too close
to Earth and was caught in
Earth’s orbit.
Fission
Theory
Early Earth spun so fast that
material broke off and formed
the Moon
Evidence that Supports the
Theory
Evidence that Does Not
Support the Theory
-Moon is close to
Earth
- Moon orbits the Sun
in the same direction
as the other planets
-Material that makes up
the Earth and Moon is
not exactly the same. If
they formed from the
same part of the nebula
they should have same
composition.
Moon does orbit the Earth.
Is possible that objects can
be trapped in orbit around
other planets (think moons
of Mars)
The object would have to
be going at exactly the
right speed and angle.
Moon rocks have similar
density and composition to
Earth’s crust and mantle
No evidence that Earth
ever spun that fast.
Would expect the object
to be irregularly shape,
but the Moon is not.
No way to explain the
core of the Moon.
Doesn’t completely
explain moon’s
composition.
Giant Impact
Theory
A large body collided with
Earth when it was in final
stages of formation.
Moon is composed of rocks
with similar composition to
Earth’s crust and mantle.
Debris from the impact came
Moon rotates and revolves
Should we
accept the
theory?
together and formed the
Moon.
in the same direction as
Earth.
It would have been so hot
that water would have
evaporated (explains why
Moon rocks are dry)