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Unit 6: Sound and space

Formation Of The Moon — HIA International - Grade 8 Revision Notes & Topical Questions

5 min read 7 parts Lesson 9 of 14 1 quiz

📚 HIA International - Grade 8 Hub / Topical Revision
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Lesson summary

Formation of the Moon — HIA INTERNATIONAL notes: Describe the collision theory for the formation of the Moon and the evidence for and against it.Fission idea — early scientists thought the Moon split away from the Earth soon after the Earth formed.Test — calculations said that th…

  • Measurement
  • Capture idea
  • Also called
  • Molten past
  • Other systems
  • Composition

Section 1 of 7Earlier ideas

Fission idea
  • Fission idea early scientists thought the Moon split away from the Earth soon after the Earth formed.
Test
  • Test calculations said that the Moon would then still be moving away from the Earth.
Measurement
  • Measurement the Moon is moving away at about 4 cm a year, but this could not completely confirm the idea.
Capture idea
  • Capture idea rejected because a captured Moon would have a different composition from the Earth.

Section 2 of 7The collision theory

1
A newly formed planet about the size of Mars, called Theia, collided with the newly formed Earth.
2
The collision broke rocks and dust away from both planets.
3
A ring of rocks and dust formed around the Earth.
4
Gravity pulled the rocks and dust together to form the Moon.
Also called
  • Also called the giant impact hypothesis, suggested in 1974.
Timing
  • Timing it happened relatively soon after the Solar System formed.
Support
  • Support there is more evidence for it than for any other current theory.

Section 3 of 7Evidence that supports the theory

Evidence that supports the theory
Density
  • Density the Moon is less dense than the Earth.
Molten past
  • Moon rock samples show its surface was once molten.
Core
  • Core the Moon has a small iron core, like the Earth.
Other systems
  • Other systems similar collisions causing rings of rock and dust are seen outside the Solar System.
Composition
  • Moon and Earth rocks have the same composition.
Consistency
  • Consistency it fits the theory of how the Solar System formed.

Section 4 of 7Evidence that contradicts the theory

Earth surface
  • Earth surface it never appears to have been molten, but the collision would have melted it.
Venus
  • Venus has no moon although collisions would have been common early on.
Rock composition
  • Rock composition the Moon’s rocks should resemble Theia’s more than the Earth’s, but they resemble the Earth’s.

Section 5 of 7How scientists work

Theory
  • Theory an explanation supported by evidence.
Change
  • Change it can change as new evidence is found.
Research
  • Research use reliable websites, check for bias and recognise secondary sources.
Not proven
  • Not proven the collision theory is the theory best supported, not proven.

Section 6 of 7Key terms

TermMeaning
Collision theoryThe idea that a planet hit the early Earth and the debris formed the Moon.
TheiaThe Mars-sized planet thought to have hit the Earth.
Giant impact hypothesisAnother name for the collision theory.
MoltenMelted by heat.
EvidenceFacts that support or contradict an idea.
CompositionWhat something is made of.

Section 7 of 7Exam technique

1
The giant impact theory is proven — it is the best supported theory.
2
Theia was an asteroid that hit the Moon — a Mars-sized planet hit the early Earth.
3
The Moon formed from the Earth’s core — it formed from outer rock, with a small iron core.
4
The Moon is getting closer — it moves away about 4 cm each year.

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