• Quick retrieval from earlier learning (The rock cycle). Students answer on mini whiteboards.
• Show answers together and note who needs support in the main task.

1. In the path from sedimentary to igneous rock, what comes straight after "buried deep and heated under pressure"? (melts to form magma / sedimentary rock / magma cools to form igneous rock / becomes metamorphic rock) → becomes metamorphic rockPrompt: Think about heat, pressure, melting, weathering and erosion.
2. Why is it called the rock "cycle"? (Rock materials are recycled from one type to another over millions of years / Rocks never change / It happens once a year / Rocks ride bicycles) → Rock materials are recycled from one type to another over millions of yearsPrompt: Can any rock type become another?
3. In the path from igneous to sedimentary rock, what comes straight after "layers of sediment build up"? (erosion carries the sediment to the sea / weathering breaks it into pieces / igneous rock at the surface / compaction and cementation form sedimentary rock) → compaction and cementation form sedimentary rockPrompt: Think about heat, pressure, melting, weathering and erosion.

• Pass round different rocks and ask how each one might have formed.
• Share the objective: The Earth's atmosphere. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: Where did most of the oxygen in today's atmosphere come from?
• Step 1: Algae and later plants released oxygen by photosynthesis.
• Step 2: So the answer is: photosynthesis by algae and plants over billions of years
• Answer: photosynthesis by algae and plants over billions of years
• Pause after each step and ask a student to say what comes next.

• Do these together. Students try each step on whiteboards before you reveal it.
• Use the hints as prompts rather than giving the answer.

1. What happened to much of the carbon dioxide in the early atmosphere? (It escaped to the Moon / It dissolved in oceans and was locked up in rocks and fossil fuels / It turned into nitrogen / It is all still in the air) → It dissolved in oceans and was locked up in rocks and fossil fuelsPrompt: Think of limestone, coal and oil.
2. Air is about 21% oxygen. About how many cm³ of oxygen are in 100 cm³ of air? → 21 cm³Prompt: Find 21% of 100.

• Students work on the student sheet. Circulate and check the first two answers of every student early.
• Students who finish: write a question of their own for a partner, with the answer.

The 8 questions are on the student sheet below, with answers in the key.

• Two questions on their own. Sort answers into got it / nearly / not yet to plan the next lesson.

1. Air is about 21% oxygen. About how many cm³ of oxygen are in 500 cm³ of air? → 105 cm³Prompt: Find 21% of 500.
2. Early Earth's atmosphere was mostly… (helium / carbon dioxide, with water vapour, released by volcanoes / argon / oxygen) → carbon dioxide, with water vapour, released by volcanoesPrompt: Volcanic activity was intense.

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-9.