12.4Earth and Space 03. Space
Describe the evidence for the collision theory for the formation of… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions
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Lesson summary
12.4 Formation of the Moon: the collision theory — CHECKPOINT - Lower Secondary Science 0893 notes: Describe the evidence for the collision theory for the formation of the Moon.Collision theory — the Moon formed about 4.5 billion years ago when a planet-sized object hit the young…
- Composition
- Low density
- Explanation
- Molten past
- Simulations
- Spin and tilt
Section 1 of 10The collision theory
Collision theory
- Collision theory the Moon formed about 4.5 billion years ago when a planet-sized object hit the young Earth.
- The impacting body is often called Theia and was roughly the size of Mars.
Debris
- Debris the impact threw molten rock and dust into orbit around the Earth.
Section 2 of 10Formation steps
1
A Mars-sized body collided with the young Earth.
2
Huge amounts of hot rock from both bodies were thrown into space.
3
The debris stayed in orbit around the Earth because of the Earth's gravity.
4
Gravity pulled the particles together, so they stuck together and grew larger.
5
The clump cooled and became the Moon.
Section 3 of 10Evidence from Moon rocks
Composition
- Composition rocks brought back from the Moon are very similar to rocks in the Earth's crust and mantle.
- This suggests the Moon was made from material that came from the Earth.
Age
- Age the Moon rocks are about 4.5 billion years old, the same age as the Earth.
Section 4 of 10Evidence from density and structure
Evidence from density and structure
Low density
- Low density the Moon is less dense than the Earth.
- It has only a small iron core.
Explanation
- Explanation the iron core of the impacting body sank into the Earth, leaving the lighter rocky outer layers to form the Moon.
Section 5 of 10Evidence from the Moon's surface
Molten past
- Molten past the Moon's surface was once molten, which agrees with a very energetic formation.
Craters
- Craters the Moon has many craters from later collisions, which shows that collisions were common in the early Solar System.
Section 6 of 10Evidence from computer models
- Simulations
- computer models of a giant collision with the Earth predict a ring of debris that forms a body like the Moon.
- Scientists use models because nobody could observe the event.
Section 7 of 10Evidence from the Earth–Moon system
Evidence from the Earth–Moon system
Spin and tilt
- Spin and tilt the Earth's spin and tilted axis are consistent with a giant impact.
Moon's orbit
- Moon's orbit the Moon orbits in the same direction in which the Earth spins.
Section 8 of 10Why a theory is accepted
- Support
- the theory is accepted because several independent pieces of evidence agree with it.
- It could change if new evidence disagrees with it.
Section 9 of 10Key terms
| Term | Meaning |
|---|---|
| Collision theory | The idea that the Moon formed from debris after a giant impact with the Earth. |
| Theia | The name given to the Mars-sized body that hit the Earth. |
| Debris | Fragments of rock and dust thrown into space. |
| Moon rock | Samples brought back from the Moon for study. |
| Density | Mass in a given volume. |
| Computer model | A simulation used to test what would happen. |
| Evidence | Facts that support or disprove an idea. |
| Crater | A bowl-shaped hole made by an impact. |
Section 10 of 10Exam technique
1
Thinking the Moon formed far away and was captured — the evidence shows it formed from material thrown out of the Earth.
2
Saying a theory is just a guess — a theory is supported by evidence.
3
Thinking the Moon is made of different material from the Earth — its rocks are very similar to Earth's mantle.
4
Confusing the collision theory with the formation of the Solar System — this theory explains only the Moon.
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