• 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 "sedimentary rock"? (buried deep and heated under pressure / becomes metamorphic rock / melts to form magma / magma cools to form igneous rock) → buried deep and heated under pressurePrompt: Think about heat, pressure, melting, weathering and erosion.
2. Molten rock beneath the Earth's surface is called… (lava / magma / sediment / marble) → magmaPrompt: It gets a different name once it erupts.
3. What makes metamorphic rock? (lava cooling quickly / heat and pressure changing existing rock without melting it / sediment settling in water / wind blowing sand) → heat and pressure changing existing rock without melting itPrompt: "Meta" means change.

• 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 is all still in the air / It dissolved in oceans and was locked up in rocks and fossil fuels / It turned into nitrogen / It escaped to the Moon) → 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 1000 cm³ of air? → 210 cm³Prompt: Find 21% of 1000.

• 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 1000 cm³ of air? → 210 cm³Prompt: Find 21% of 1000.
2. Which gas makes up most of the air we breathe? (carbon dioxide / oxygen / nitrogen / hydrogen) → nitrogenPrompt: It is about four-fifths of the air.

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