• 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"? (becomes metamorphic rock / magma cools to form igneous rock / melts to form magma / buried deep and heated under pressure) → buried deep and heated under pressurePrompt: Think about heat, pressure, melting, weathering and erosion.
2. Why is it called the rock "cycle"? (It happens once a year / Rocks ride bicycles / Rocks never change / Rock materials are recycled from one type to another over millions of years) → 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 "igneous rock at the surface"? (layers of sediment build up / erosion carries the sediment to the sea / weathering breaks it into pieces / compaction and cementation form sedimentary rock) → weathering breaks it into piecesPrompt: 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 is all still in the air / It turned into nitrogen / It dissolved in oceans and was locked up in rocks and fossil fuels) → 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 500 cm³ of air? → 105 cm³Prompt: Find 21% of 500.

• 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. Where did most of the oxygen in today's atmosphere come from? (the oceans boiling / the Sun / volcanoes / photosynthesis by algae and plants over billions of years) → 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 1000 cm³ of air? → 210 cm³Prompt: Find 21% of 1000.

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