Formation of the Moon
Lesson notes
Overview
A Mars-sized body probably struck the early Earth, throwing out debris that formed the Moon. This topic is rated intermediate and is number 84 of 98 in Earth & Space. Builds on the basics with relationships, methods and trade-offs.
What you are seeing
The panel above shows the steps of a process, laid out in order. Click a step to see what happens next. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
The giant impact hypothesis holds that about 4.5 billion years ago a Mars-sized body, called Theia, struck the young Earth. The debris from both bodies went into orbit and gathered into the Moon. It explains why the Moon is made of material similar to Earth’s mantle, has a small iron core, and why the Earth–Moon system has a large angular momentum. The Moon’s stabilising effect on Earth’s tilt may have been important for the stable climate of Earth.
Reading the relationship
The expression "giant impact hypothesis" is a compact summary of the idea. It uses the symbols g, i, a, n, t, m; name what each one stands for before you start. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Predict the outcome first, then test extreme slider values to find where the pattern changes or breaks.
Common pitfalls
Earth and space systems work on very different scales of time and distance. Check which scale a number refers to before comparing it with another.
How it connects
It builds on “Formation of the Solar System”, the topic before it in Earth & Space. Once you are comfortable, continue with “How Supernovae Create Elements”.
Why it matters
Earth and space science helps us understand our planet, its climate and the wider universe.
Where you might use it
- Revising “Formation of the Moon” before a class, exam or certification
- Forecasting weather and understanding climate records and their uncertainty
- Planning for earthquakes, floods and other natural hazards in cities
- Interpreting satellite images, space missions and the age of rocks and stars
Frequently asked questions
What is Formation of the Moon?
A Mars-sized body probably struck the early Earth, throwing out debris that formed the Moon. It is an intermediate topic in Earth & Space.
How do I use the Formation of the Moon simulation?
The panel at the top shows the steps of a process, laid out in order. Click a step to see what happens next. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression giant impact hypothesis packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Builds on the basics with relationships, methods and trade-offs. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “Formation of the Solar System”, the previous topic in Earth & Space. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.