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

1. In how a fossil forms, what happens straight after "the soft parts rot away"? (it is quickly buried by mud or sand / an animal dies / the rock is worn away and the fossil is uncovered / minerals slowly replace the bones over millions of years) → minerals slowly replace the bones over millions of yearsPrompt: Only the hard parts usually become fossils.
2. Why do most fossils show bones, teeth and shells rather than skin? (Skin turns into rock straight away / Hard parts last longer; soft parts rot quickly / Animals had no skin / Scientists remove the skin) → Hard parts last longer; soft parts rot quicklyPrompt: Which parts of an animal rot first?
3. In how a sea shell becomes a fossil, what happens straight after "its shell sinks to the sea floor"? (layers of sediment cover it / a sea creature dies / the fossil is found in the rock millions of years later / the sediment slowly turns into rock) → layers of sediment cover itPrompt: Fossils form very slowly, buried in rock.

• Pass round different rocks and ask how each one might have formed.
• Share the objective: Rock layers: reading time from the bottom up. Read the success criteria together.

• Work through the example out loud, saying why you do each step, not just what you do.
• Example: At the bottom of a lake, mud builds up about 2 cm every 100 years. A layer of mud is 22 cm thick. About how many years did it take to form?
• Step 1: 22 ÷ 2 = 11
• Step 2: 11 × 100 = 1100
• Step 3: So the answer is: 1100
• Answer: 1100
• 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. At the bottom of a lake, mud builds up about 5 cm every 100 years. A layer of mud is 45 cm thick. About how many years did it take to form? → 900Prompt: How many groups of 5 cm are in 45 cm?
2. A fossil is found in a layer deep below another layer. Which fossil is older? (you can never tell / the one in the higher layer / the one in the deeper layer / they are the same age) → the one in the deeper layerPrompt: Which layer was there first?

• 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 6 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. A fossil is found in a layer deep below another layer. Which fossil is older? (the one in the deeper layer / you can never tell / they are the same age / the one in the higher layer) → the one in the deeper layerPrompt: Which layer was there first?
2. At the bottom of a lake, mud builds up about 2 cm every 100 years. A layer of mud is 18 cm thick. About how many years did it take to form? → 900Prompt: How many groups of 2 cm are in 18 cm?

Free online practice with hints and printable worksheets for this skill: eurekami.com/science/grade-4.