• 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 igneous to sedimentary rock, what comes straight after "erosion carries the sediment to the sea"? (layers of sediment build up / compaction and cementation form sedimentary rock / weathering breaks it into pieces / igneous rock at the surface) → layers of sediment build upPrompt: 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 ride bicycles / Rocks never change / It happens once a year) → Rock materials are recycled from one type to another over millions of yearsPrompt: Can any rock type become another?
3. In the path from sedimentary to igneous rock, what comes straight after "sedimentary rock"? (becomes metamorphic rock / buried deep and heated under pressure / magma cools to form igneous rock / melts to form magma) → buried deep and heated under pressurePrompt: 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. Where did most of the oxygen in today's atmosphere come from? (photosynthesis by algae and plants over billions of years / the oceans boiling / the Sun / volcanoes) → photosynthesis by algae and plants over billions of yearsPrompt: Early Earth had almost no oxygen.
2. Air is about 21% oxygen. About how many cm³ of oxygen are in 200 cm³ of air? → 42 cm³Prompt: Find 21% of 200.

• 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. 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 100 cm³ of air? → 21 cm³Prompt: Find 21% of 100.

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